Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • 1995-1999  (634)
  • 1998  (634)
  • Theoretical, Physical and Computational Chemistry  (583)
  • Chemical Engineering
  • Nuclear reactions
Source
Material
Years
  • 1995-1999  (634)
Year
Keywords
  • 201
    Electronic Resource
    Electronic Resource
    The interface of electronic structure and dynamics for reactions in solution (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 887-896 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We compare two systematic approaches to the calculation of reaction rates in liquid solutions: the separable equilibrium solvation (SES) approximation and the equilibrium solvation path (ESP) approximation. These approaches are tested for two reactions, ClCH3+NH3→Cl-+H3CNH3+ (R1) and NH4+…N′H3→NH3…N′H4+ (R2), both in aqueous solution. The first reaction illustrates the importance of variational optimization of the transition state, and the second illustrates the importance of tunneling. Free energies of solvation are calculated by the Solvation Model 5. All calculations are carried out by the new AMSOLRATE program, which is an interface of the AMSOL and POLYRATE programs.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 887-896, 1998
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 202
    Electronic Resource
    Electronic Resource
    Intramolecular proton transfer in monohydrated tautomers of cytosine: An ab initio post-Hartree-Fock study (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 855-862 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The results of an ab initio post-Hartree-Fock study of the molecular structures, relative stabilities, and mechanisms of intermolecular proton transfer in isolated and monohydrated cytosine complexes are reported. The geometries of the local minima and transition states were optimized without symmetry restrictions by the gradient procedure at the HF and the MP2 levels of theory and were verified by energy second-derivative calculations. The standard 6-31G(d) basis set was used. The single-point calculations were performed at the MP4(SDQ)/6-31+G(d, p)//MP2/6-31G(d) and MP2/6-311++G(d, p)//MP2/6-31G(d) approximations. All values of the total energies were corrected for scaled zero-point energy contributions. The post-Hartree-Fock ab initio theory predicts the height of the proton-transfer barrier for monohydrated cytosine complexes to be approximately three times lower for the tautomeric oxo-hydroxo reaction compared with non-water-assisted processes. The influence of polar media (Onsager's self-consistent reaction-field model) slightly changes these values according to the order of the stability of the tautomers in a polar solution. The interaction with one water molecule changes the order of the relative stability of cytosine tautomers from the gas phase to the one which corresponds to the experimentally measured relative stabilities in polar solutions. In contrast to guanine, we did not find significant water influence on the NH2-nonplanarity phenomena.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 855-862, 1998
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 203
    Electronic Resource
    Electronic Resource
    Intramolecular hydrogen bonding in resonance-stabilized systems (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 863-875 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 3-substituted-2-methoxybenzoic acid system exhibits resonance-stabilized intramolecular hydrogen bonding between the 2-methoxy oxygen and the adjacent carboxylic acid. This intramolecular hydrogen bond can be disrupted by adding another substituent with variable size on the neighboring 3-position of the ring. To relieve steric strain, the system must sacrifice hydrogen bonding and/or resonance stabilization. Full-energy optimizations have been done at HF/D95V (valence double-zeta Dunning-Huzinaga), HF/6-31G* (Pople), HF/D95 (full double-zeta Dunning-Huzinaga), HF/D95V(d, p), and HF/6-31+G(d, p). Further single-point calculations were done at MP2/D95V, MP2/6-31G*, MP2/D95, MP2/D95V(d, p), and MP2/6-31+G(d, p). The thermal populations of various conformational states including the hydrogen-bonding conformation are presented. The computational results were compared with the experimental thermal population of hydrogen bonding determined by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies. Results indicate that polarization of the second-row elements in intramolecular hydrogen bonding and perturbation-theory calculations that correct for electron correlations are very important for intramolecular hydrogen bonding. Adding polarization and diffuse functions to the hydrogens, while useful, are quite costly for these systems and do not seem to be as important.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 863-875, 1998
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 204
    Electronic Resource
    Electronic Resource
    Quantum chemical study of the interaction of nitrate anion with water (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 877-886 
    Details
    ISSN: 0020-7608
    Keywords: potential functions ; nitrate anion ; nitrate-water interaction ; nitrate-water cluster geometries ; vibrational frequencies ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction between nitrate anion and water has been investigated by Hartree-Fock calculations with the 6-311+G(d, p) basis set and by B3LYP density functional calculations with the aug-cc-pVTZ basis set. It is found that the global energy minimum is a planar configuration where both hydrogen atoms of water are coordinated to two oxygen atoms of NO3- by distorted hydrogen bonds. In contrast to former studies on NO3-/H2O this configuration is found to be asymmetric at the highest theoretical level employed. The corresponding structure with C2v symmetry is a saddle point at slightly higher energy. A singly hydrogen-bonded configuration is still about 2.4 kcal/mol higher in energy. The shifts in the vibrational frequencies of water and nitrate upon complexation were calculated. A compact analytical potential function of NO3-/H2O for use in statistical thermodynamic simulations was obtained from 390 points of the energy surface and an intramolecular force field for the nitrate anion is presented.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 877-886, 1998
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 205
    Electronic Resource
    Electronic Resource
    The development of semiclassical dynamical methods and their application to vibrational relaxation in condensed-phase systems (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 897-907 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A semiclassical surface-hopping propagator for problems involving nonadiabatic transitions is discussed. The propagator is employed in expressions for the probability of transitions between quantum states of molecules in condensed phases. This approach is implemented for the evaluation of the rate of vibrational transitions in liquids, dense gases, and clusters. Results for the rates of relaxation of excited vibrational states of a molecule in a simple solvent are discussed. The use of computationally simplifying short-time approximations for the solvent dynamics are considered. These approximations are tested using calculations on simple model systems. It is found that these simplifying approximations work well as long as the energy difference between the initial and final quantum states is not small. Calculations are also performed for the probability of resonant transfer of vibrational excitation energy between molecules in clusters using a mixed quantum-classical calculational procedure. It is found that quantum coherence effects are observed for several picoseconds in the probability for resonant transfer in these systems.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 897-907, 1998
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 206
    Electronic Resource
    Electronic Resource
    Bethe-Bloch stopping-power parameters for GaAs and ZnSe (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 919-924 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: If one is to calculate the stopping power for a specified projectile-target combination within the energy interval of applicability of modified Bethe-Bloch theory, values of several parameters appearing in the formulation must be ascertained. In the past, the author has established such values for numerous target materials through fits of stopping-power measurements with modified Bethe-Bloch theory. However, the semiconductor materials ZnSe and GaAs have not yet been thus characterized. A set of very recent measurements of the stopping powers of each compound for low-energy protons and alpha particles, reported by members of the Helsinki group, has been analyzed in order to remedy this dearth of parameter values. Moreover, some corresponding measurements for 7Li ions traversing ZnSe have been analyzed for the purpose of obtaining the value of a single effective charge parameter. Results of these studies are reasonably consistent with expectations, and values are recommended for the mean excitation energy and the Barkas-effect parameter for each compound.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 919-924, 1998
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 207
    Electronic Resource
    Electronic Resource
    Single-electron-capture cross sections by alpha-particles from ground state K(4s) and Rb(5s): A molecular-state approach (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 909-917 
    Details
    ISSN: 0020-7608
    Keywords: charge transfer ; α-particles ; alkali atoms ; MO expansion ; close coupling ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cross sections for single-electron capture by α-particles from ground state K and Rb were calculated in the low-to-intermediate energy region by employing the molecular expansion method in the framework of impact parameter formulation. The colliding partners are treated as a pseudo-one-electron system and the technique of the pseudopotential is used to account for their mutual interactions. The molecular wave function of the quasimolecule formed during the collision is expanded in terms of basis sets of atomic orbitals on two centers. The resulting coupled equations are solved semiclassically where a straight-line trajectory describes the relative motion of the two nuclei. The effect of electron translation is also suitably incorporated. The calculated cross sections, both total and partial, are presented and compared with the available experimental measurements.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 909-917, 1998
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 208
    Electronic Resource
    Electronic Resource
    Searches on the potential energy hypersurfaces of GeCH2, GeSiH2, and Ge2H2 (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 925-932 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optimum geometries are computed at both the SCF level of theory and the level of second-order perturbation theory for several isomers on the potential energy hypersurfaces of GeCH2, GeSiH2, and Ge2H2, including linear structures, methylene-carbenelike structures, dibridged structures, and monobridged structures. In addition, harmonic vibrational frequencies are computed to characterize these structures as local minima or transition states. All computations employ basis sets of triple-zeta quality on valence electrons with d and f polarization functions on the heavy atoms and p functions on hydrogen. This investigation is the first systematic study to include all of these germanium systems and to employ f-type polarization functions in such a study. Previous investigations of ours indicate that large basis sets such as those employed in this study can, in part, compensate for the lack of a more advanced treatment of electron correlation. While a dibridged global minimum is confirmed for both Ge2H2 and GeSiH2 systems, the C2v isomer, methylenegermene, is found to be the most stable structure for GeCH2.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 925-932, 1998
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 209
    Electronic Resource
    Electronic Resource
    Excited-state potential energy curves from time-dependent density-functional theory: A cross section of formaldehyde's 1A1 manifold (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 933-941 
    Details
    ISSN: 0020-7608
    Keywords: time-dependent density-functional theory ; excited state surfaces ; avoided crossings ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work reports the first density-functional theory (DFT) treatment of excited-state potential energy surfaces exhibiting avoided crossings. Time-dependent DFT (TD-DFT) results, using a recently proposed asymptotically corrected local density approximation functional, are compared with multireference doubles configuration interaction (MRD-CI) results for the 1A1 manifold of the CO stretching curves of planar formaldehyde. TD-DFT is found to reproduce the qualitative features essential for understanding the spectroscopy of this manifold, specifically the strong mixing of the 1(π, π*) with Rydberg transitions and the resultant avoided crossings.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 933-941, 1998
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 210
    Electronic Resource
    Electronic Resource
    Effective potential for e-neon and e-argon scattering by DCS minimization at intermediate energies (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 943-950 
    Details
    ISSN: 0020-7608
    Keywords: electron scattering ; effective potential ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The differential scattering cross-section (DCS) for electrons scattered elastically by neon and argon atoms is studied using a model potential. In the present study the long-range polarization potential is represented by an energy-dependent function, and the short-range part is constructed from the nonrelativistic Hartree-Fock wave function of the target atom. The computed differential cross section obtained using the approximate effective interaction potential for electrons scattered by neon and argon atoms in their ground state is compared with available published results. In the present study the parameters contained in the energy-dependent effective potential are determined by the minimization of the DCS with respect to angle θ and the incident energy. The resulting DCS in the angular range 2°〈θ〈178° is found to be in good agreement with the available experimental and theoretical results in the intermediate energy range.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 943-950, 1998
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 211
    Electronic Resource
    Electronic Resource
    Singlet-triplet splitting and the activation of C—H bond for (η5-C5H5)M(CO) isoelectronic fragments: A theoretical study (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 961-971 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A density functional study was used to investigate potential energy surfaces of the oxidative addition reaction CpM(CO)+CH4→CpM(CO)(H)(CH3) (M=Ru-, Os-, Rh, Ir, Pd+, and Pt+). A qualitative model which is based on the theory of Pross and Shaik was applied to develop an explanation for the barrier heights. As a result, our theoretical findings suggest that the singlet-triplet splitting (ΔEst=Etriplet-Esinglet) of the CpM(CO) species can be a guide to predict its reaction activity and enthalpy for oxidative additions. A better linear correlation was found between the latter two quantities. Considering the nature of the metal center, the following conclusions therefore emerged: For the 16-electron CpM(CO) system, a heavier transition-metal center (i.e., the third-row) will lead to a smaller ΔEst and, in turn, will facilitate the oxidative addition reactions to alkane C—H bonds. In contrast, a lighter transition-metal center (i.e., the second row) will result in a larger ΔEst and then tend to undergo the reductive elimination reactions of the C—H bond-forming. The results obtained are in good agreement with the available experimental results and allow a number of predictions to be made.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 961-971, 1998
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 212
    Electronic Resource
    Electronic Resource
    Structural and electronic properties of silicon nitride materials (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 973-980 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We developed an empirical potential for interactions between Si and N to describe silicon nitride systems using the Tersoff functional form. With this model, we explored the structural properties of amorphous silicon nitride through the Monte Carlo simulations and compared them to available experimental data. The empirical model provided a very good description of such properties for a-SiNx (0〈x〈1.5). Electronic structure of amorphous and point defects in crystalline silicon nitride were then studied using first-principles calculations. For such calculations, the configurations were created by the empirical model, with the relaxed structures used as input for the first-principles calculations. Atomic relaxation was later allowed in the first-principles calculations.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 973-980, 1998
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 213
    Electronic Resource
    Electronic Resource
    Ab initio SCF-MO study of the topology of the charge distribution of acid sites of zeolites (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 951-960 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structural, electronic, vibrational, and topologic properties of a series of acid sites of zeolites were studied at different levels of ab initio molecular orbital theory. The zeolite acid sites were modeled by using the following molecular clusters: silanol H3SiOH (B0) and the clusters H3SiO(H)AlH3 (B1), (OH)3SiO(H)Al(OH)3 (B1―OH), and H3SiO(H)Al(OH)2SiH3(B2). The calculation of geometries and properties of these clusters were performed at the Hartree-Fock level, and, additionally, second-order Møller-Plesset (MP2) and density functional BLYP calculations were carried out for silanol and B1 clusters. Geometries were fully optimized by following Cs symmetry restrictions. The standard STO/6-31+G(D, P) basis set, which includes polarization and diffuse functions, was used for all the calculations. The topologic properties of the zeolite acid clusters, based on the theory of atoms in molecules, were analyzed in terms of the total density and the Laplacian density properties, both evaluated at the position of the bond critical points. The calculations showed that the frequency of the OH vibrational modes of the zeolite acid sites, often used as an infrared index for characterizing the acidity of zeolites, is linearly related to the total density of the charge at the critical points of the OH bonds, with a correlation coefficient of r2=0.97. These results indicate that the total density of the electronic charge at the critical point of the OH bond can be used as a tool for interpreting the structural and electronic features of the zeolite hydroxyl groups. A relationship between the Mulliken population of the H atom of the OH bond and the OH frequency gives a correlation coefficient of 0.67. On the other hand, the values of the Laplacian density calculated at the critical points of the bonds of the acid sites indicate that the zeolite structure is dominated by a network of Si—O and Al—O ionic interactions, while the O(SINGLE BOND)H bonds are characterized as covalent bonds, with different extents of charge concentration.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 951-960, 1998
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 214
    Electronic Resource
    Electronic Resource
    Approximations of the Mulliken charges for the oxygen and silicon atoms of zeolite frameworks calculated with a periodic Hartree-Fock scheme (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 993-1001 
    Details
    ISSN: 0020-7608
    Keywords: Mulliken charges ; zeolite ; periodic Hartree-Fock ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Distributed multipole analysis (DMA) on the basis of periodic Hartree-Fock (PHF) calculations, using the CRYSTAL code, is applied to five different all-siliceous zeolite models: chabazite, gmelinite, merlinoite, montesommaite, and RHO. Mulliken charges of the framework atoms were calculated with a pseudopotential ps-21G* basis set for silicon and a 6-21G* basis for oxygen. The charge values of the silicon atoms were approximated by a simple one-dimensional function with respect to the average Si—O distance within the respective SiO4 tetrahedra, whereas a two-dimensional function with respect to the average Si—O distance and the Si—O—Si angle was used for the oxygen atoms. Both dependences were then utilized to evaluate the Mulliken atomic charges of 10 other frameworks with a larger number of atoms per unit cell. The validity of such application is confirmed by comparison with results obtained through direct PHF calculation for all-siliceous mordenite.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 993-1001, 1998
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 215
    Electronic Resource
    Electronic Resource
    Structure and properties of NH52+: A dication with two 2-electron 3-center bonds (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1003-1007 
    Details
    ISSN: 0020-7608
    Keywords: dications ; coupled-cluster calculations ; penta coordinate nitrogen ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dication NH52+ has been studied by state-of-the-art quantum chemical techniques. NH52+ is a square-based pyramid with C4v symmetry. The apical H is bonded to N with a 2-electron covalent bond, while the other H atoms are bonded to N through degenerate 2-electron 3-center bonds. No other local minimum exists on the potential energy surface. A C2v transition state linking equivalent C4v structures is only 1.35 kcal mol-1 higher in energy. The barrier to deprotonation is 26.4 kcal mol-1.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1003-1007, 1998
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 216
    Electronic Resource
    Electronic Resource
    Analysis of three-dimensional molecular shape using surface area and molecular volume scaling descriptors (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 981-992 
    Details
    ISSN: 0020-7608
    Keywords: molecular similarity ; electron density contours ; fused-sphere surfaces ; van der Waals radii ; hydrocarbons ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Continua of molecular surfaces have been proposed in the past as realistic approaches to modeling molecular shape. A continuum of fused-sphere surfaces combines the simplicity of computations involving hard spheres with a more accurate description of the “fuzzy” boundary of a molecule. In this work, we study some simple properties of a continuum of molecular surfaces derived by linearly scaling the van der Waals radii. We introduce some molecular shape descriptors derived from surface area and volume and study their dependence on a scaling parameter that “swells” the molecular surface. As one moves away from the nuclei, any transitions in molecular shape are reflected by changes in the descriptors. These descriptors convey essential shape features, in the sense that they are rather insensitive to molecular size. Even though the geometrical descriptors characterize the continuum globally, their behavior appears to be strongly determined by local molecular shape features. The procedure can also be extended to more realistic electron density surfaces. As a tool, the method can be helpful in assessing molecular similarity, as well as in studying properties of local neighborhoods within large clusters.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 981-992, 1998
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 217
    Electronic Resource
    Electronic Resource
    C60 carbyne knots (from 01 to 63): Theoretical NMR spectra (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1009-1015 
    Details
    ISSN: 0020-7608
    Keywords: ab initio ; carbon allotrope ; carbyne ; 13C-NMR ; topological isomerism ; knot ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure, stability, and theoretical 13C- NMR spectra of nonlinear C60 carbon clusters of the carbyne type have been estimated by ab initio calculations. Semiempirical AM1 calculations have shown the knot-cycle energy difference to increase with the number of knot crossings and to decrease with the number of atoms constituting the molecule. Some C60 carbyne prime knots belong to the following symmetry point groups: D30h for cycle, D3 for trefoil, C1 for figure eight (but S4 for the C64 figure eight), C2 for cinquefoil and the other five-crossing knot, and C1 for six crossing knots. Knot symmetry and the calculated 13C-NMR qualitative spectra provide the basis for experimental identification of the knotted carbyne structures.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1009-1015, 1998
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 218
    Electronic Resource
    Electronic Resource
    Perturbed ellipsoidal wave functions for quantum scattering (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1017-1022 
    Details
    ISSN: 0020-7608
    Keywords: scattering ; ellipsoidal coordinates ; Fourier method ; Lamé wave functions ; optical theorem ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The scattering data of a potential, separable in ellipsoidal coordinates, are expanded in perturbed Lamé wave functions. These functions arise when variables in the Schrödinger equation are separated in the ellipsoidal coordinate system. Preliminary calculations are displayed for the total cross section and the scattering amplitude versus direction. The quicker the potential vanishes at infinity the more pronounced is the dependence on the incident direction.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1017-1022, 1998
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 219
    Electronic Resource
    Electronic Resource
    Photochemical reaction pathways of ethylene (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1023-1028 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conical intersections are a common feature in most nondiabatic singlet photoreactions. For ethylene, several S1-S0 conical intersections could be located by CASSCF calculations. The energetically lowest one is different from the one determined by Ohmine [J. Chem. Phys. 83, 2348 (1985)]; its geometry suggests that cis-trans isomerization and a [1,2]hydrogen shift occur via the same funnel.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1023-1028, 1998
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 220
    Electronic Resource
    Electronic Resource
    Theoretical studies on hydrogen activation by iridium dimers (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1029-1035 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The basic and fundamental mechanisms governing the catalytic reaction of small iridium clusters with H2 are presented here with the purpose to determine its behavior in hydrogenation reactions. The iridium dimer/s lowest states in interaction with H2 potential energy surface were obtained using ab initio multiconfigurational self-consistent-field calculations (MC-SCF), with relativististic pseudopotentials. The electronic correlation contribution was included by configurations interaction (CI) calculations, which considered a variational part plus a second-order perturbative part. The Ir2+H2 reactions were developed in the C2v symmetry. The Ir2's five lowest electronic states were determined, 5Πg, 3Πg, 1Σg+, 3Σu+, and 5Σg, and studied when reacted with H2. It was found that the iridium dimer, in these five states, might capture and break the H—H bond, spontaneously in certain cases and after surmounting activation barriers in other cases.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1029-1035, 1998
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 221
    Electronic Resource
    Electronic Resource
    Electron propagator theory of conformational effects on anisole and thioanisole photoelectron spectra (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1037-1043 
    Details
    ISSN: 0020-7608
    Keywords: anisole ; thioanisole ; conformations ; propagator theory ; photoelectron spectra ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electron propagator calculations in two diagonal self-energy approximations, partial third order and the outer valence Green/s function, are employed in interpretation of the photoelectron spectra of anisole and thioanisole. Major features of the spectra are accurately predicted and are associated to canonical molecular orbitals. Contributions from planar and orthogonal rotational structures are responsible for minor features of the spectra that are dependent on temperature. Correlation effects are large and change the order of final states in thioanisole. Partial third-order calculations are more accurate than outer valence Green/s function results.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1037-1043, 1998
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 222
    Electronic Resource
    Electronic Resource
    Periodic INDO calculations of organic adsorbates on a TiO2 surface (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1055-1066 
    Details
    ISSN: 0020-7608
    Keywords: periodic INDO ; bi-isonicotinic acid ; adsorption ; TiO2 surface ; rutile ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new parametrization for use in periodic semiempirical quantum-chemical INDO calculations is proposed. Parameter sets for C and N atoms are tested on a number of C- and N-containing molecules, giving reasonably good agreement with experimental data and/or ab initio results. The new parametrization is intended for studies of organic adsorbates on oxide surfaces using a periodic large unit cell (LUC) model. As an example, two possible adsorption geometries for bi-isonicotinic acid on a TiO2 rutile(110) surface were investigated, and structural effects involved in the adsorption are discussed.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1055-1066, 1998
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 223
    Electronic Resource
    Electronic Resource
    Advantages of the Fourier space RHF band structure approach: Application to polyoxymethylene using a distributed basis set of s-type Gaussian functions (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1045-1054 
    Details
    ISSN: 0020-7608
    Keywords: restricted Hartree-Fock ; Fourier space ; Gaussian-type functions ; polymers ; band structure ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this contribution, we outline the Fourier space-restricted Hartree-Fock (FS-RHF) approach to the calculation of the band structure of polyoxymethylene (POM) using a distributed basis set of s-type Gaussian functions (DSGF) to simulate p-type functions. The band structure results are compared to those obtained using minimal STO-3G basis sets, within the conventional RHF direct space (DS) approach, and subminimal floating spherical Gaussian orbital (FSGO) basis sets. While the FSGO basis sets are unable to describe correctly the oxygen lone pairs and their interactions, the DSGF basis set reproduces qualitatively the features of the band structure observed with the minimal basis set. We show that minor differences between the FS and DS results originate in difficulties of lattice summations within the DS approach, illustrating the advantages of the FS method compared to the conventional DS approach.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1045-1054, 1998
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 224
    Electronic Resource
    Electronic Resource
    Sign of the interaction parameter in disordered Fe-Al alloys (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1067-1073 
    Details
    ISSN: 0020-7608
    Keywords: Fe-Al alloys ; electronic structure calculations ; ordering ; phase transitions ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the framework of the coherent potential approximation we show that the interaction parameter for disordered Fe-Al alloy strongly depends on the concentration. The calculations were provided within linear muffin-tin orbital formalism in the atomic sphere approximation. Calculation data for B2 phase for different concentrations were used to extract the interaction parameter, V(0), for disordered solid solutions and were compared with the parameter treated from the X-ray scattering data. The concentration dependence of V(0) leads to the failure of the application of the regular solid solution model to the study of the phase relations in the Fe-Al system. Parameter V(ks), which is responsible for ordering tendency, also depends on concentration, and it is in accordance with the experimental data.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1067-1073, 1998
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 225
    Electronic Resource
    Electronic Resource
    Possibility of charge-mediated superconductors in the intermediate region of metal-insulator transitions (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1075-1084 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some molecular systems for a charge-mediated superconductor are proposed from the viewpoint of the metallic side and the insulator side. An approach to the charge-transfer (CT) model is presented. Expressions of the effective electron-electron interaction in the charge-fluctuation models is also derived by a field-theoretical approach.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1075-1084, 1998
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 226
    Electronic Resource
    Electronic Resource
    Embedded cluster and supercell study of the structure of the interstitial Cu-C solid solutions (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1085-1092 
    Details
    ISSN: 0020-7608
    Keywords: electronic structure calculations ; microstructure ; composites ; solid solutions ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preferable carbon occupation in copper-based solid solutions is modeled in different Cu—C lattice cells and clusters. A study is based on the comparative analysis of electronic density distributions for different interatomic distances, supercell configurations, and compositions of carbon. For these solid solutions we use the linear muffin-tin orbitals (LMTO) and discrete variation method (DVM) computer codes which allow us to calculate equilibrium positions of carbon atoms. We study the concentration dependence of the lattice parameter in Cu—C solid solution and discuss the charge transfer in this system.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1085-1092, 1998
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 227
    Electronic Resource
    Electronic Resource
    Atomic motion at germanium surfaces: Scanning tunneling microscopy and Monte Carlo simulations (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 1093-1097 
    Details
    ISSN: 0020-7608
    Keywords: surface ; STM ; germanium ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The observation of the motion of an adatom on the reconstructed Ge (111) is a rare event, which will be examined by way of simple adatom-surface interaction models. Estimations of the residence time of adatoms on energetically favorable sites indicate that a thermal excitation can account for casual adatom motion and that a strong tip-surface interaction is not obviously needed to explain the changes found in sequences of scanning tunneling microscopy (STM) images of the same surface areas.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 1093-1097, 1998
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 228
    Electronic Resource
    Electronic Resource
    Transportation of hazardous wastes (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 17 (1998), S. 61-67 
    Details
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Risk assessments have been performed to determine the risk associated with the transportation of hazardous wastes through a city. In the course of these assessments, a number of modeling issues arose relating to transportation accident rates, the characterization of incidents, the effect of thermal radiation, the impact of exposure to toxic chemicals, and the threshold for acceptable risk. This paper discusses these issues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prs.680170112
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 229
    Electronic Resource
    Electronic Resource
    Process safety update (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 17 (1998), S. S3 
    Details
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prs.680170202
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 230
    Electronic Resource
    Electronic Resource
    Burst resistant ribbon wound pressure vessels for ammonia plants (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 17 (1998), S. 98-103 
    Details
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper presents the design of ribbon wound pressure vessels useful for Ammonia, Urea and Methanol plants. The design is to create a thin shell of 1/5 the total wall thickness required, weld it to the end pieces, and wind 4 to 8 mm thick ribbons of 80 mm width at an angle of 15 to 30 degrees on the inner shell, using a prestress. The ribbons are welded at the ends and an even number of layers are wound cross-helically on to the shell. With more than 7000 vessels over the pressure range of 50 to 350 atmospheres in use in the various chemical industries in China over the past 30 years, their safety record has been excellent. Of particular interest has been the application of this technology in the Ammonia and Urea plants, where the design allows fabrication of these vessels at substantial reduction in cost, and early delivery, when compared to the mono wall technology.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prs.680170205
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 231
    Electronic Resource
    Electronic Resource
    Safety surveys - looking at key activities in depth (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 17 (1998), S. 20-22 
    Details
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Most audits try to look at a representative selection of the plant procedures and equipment. An alternative is a survey, a look in depth at selected procedures (such as those for testing alarms and trips, issuing permits-to-work, controlling modifications, taking samples or testing relief devices) or selected equipment (such as level glasses or equipment for handling LPG). If the procedure or equipment is well-chosen, surveys may make a bigger contribution to safety, per person-hour, than a conventional audit.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prs.680170106
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 232
    Electronic Resource
    Electronic Resource
    Pressure relief system documentation: Equipment based relational database is key to OSHA 1910.119 compliance (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 17 (1998), S. 39-42 
    Details
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Under OSHA 1910.119, all Process Safety Management (PSM) facilities are required to keep their pressure relief system design information current. This article demonstrates why a pressure relief system design verification effort must be based on an equipment list, rather than a relief device list, in order to ensure that every piece of equipment is adequately protected. The formerly common practice of simply checking the design bases of all existing relief devices is deficient is deficient since this technique does not systematically ensure that every piece of equipment is protected.The “Berwanger Method” is a step by step process for designing or analyzing a pressure relief system to meet OSHA 1910.119 Process Safety Information (PSI) and Process Hazard Analysis (PHA) mandates. The method uses a relational database which tracks the relationships between protected equipment, potential overpressure scenarios, and protective devices.The challenge facing an operating company does not end once the design basis has been “verified” - the design basis information must also be maintained and be readily accessible to avoid costly reinvention of the wheel down the road. The “Berwanger Method” also addresses these maintenance issues.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prs.680170109
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 233
    Electronic Resource
    Electronic Resource
    A detailed reaction study of phosphorus trichloride and water (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 17 (1998), S. 49-60 
    Details
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper reports on a comprehensive literature search and small scale experimental work on the reaction characteristics of phosphorous trichloride and water. More than 30 tests were conducted, including both closed and open test cells. The water to phosphorus trichloride molar ratio was varied from 1 to 25. When in contact, water and phosphorus trichloride will form two liquid layers with a reaction starting at the interface. The impact of variables on reaction rates including the interface surface area, layer depth, and stirring were investigated experimentally. A reaction rate model that fits all the measured data is presented. Case studies illustrating the use of this data for emergency relief systems and vent containment design are presented in reference. [1].
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prs.680170111
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 234
    Electronic Resource
    Electronic Resource
    The influence of the geometry of the hot surfaces on the autoignition of vapor/air mixture: Some experimental and theoretical results (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 17 (1998), S. 68-73 
    Details
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Two major accidents in the 80's: the summit Tunnel Fire, England and Piper Alpha disaster, an offshore platform in the North Sea; and very recently, possible explosion of the Boeing, TWA flight 800 at New York, makes it imperative that further research into the mechonisms of the ignition of flammable vapor/air mixture in contact with hot surfaces needs to be done. There have been a number of studies of ignition by hot surfaces, but in all these studies the ignition sources were wire, sphere or strip, i.e., most of them were flat surfaces. But to the authors' knowledge, other variables which affect the ignition mechanism such as irregular geometrical shapes have not been studied. The purpose of this paper is to examine how the degree of confinement (or, configuration), size and orientation, of the heated surface affects the ignition temperature of the flammable vapors. The results were obtained by experimentnal and by computational fluid dynamics.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prs.680170113
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 235
    Electronic Resource
    Electronic Resource
    Mechanism of formation of benzothiazole-2-thiol (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 1-9 
    Details
    ISSN: 0894-3230
    Keywords: benzothiazole-2-thiol ; formation mechanism ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The formation of benzothiazole-2-thiol from aniline, carbon disulphide and sulphur at 230°C was shown to occur by a sequence of three principal steps. Labelling experiments confirmed that both sulphur atoms originate from carbon disulphide. An initial polar reaction to form thiocarbanilide via phenylcarbamic acid and a tetrahedral intermediate is followed by radical cyclization of these to benzothiazole-2-thiol and 2-phenylaminobenzothiazole; the latter is converted into the desired product by a polar displacement of aniline by H2S. Mechanisms for the formation of minor byproducts are also considered. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 236
    Electronic Resource
    Electronic Resource
    Reactions of 1,ω-bis(2-bromopyridinium)alkanes with hydroxide ion in aqueous solutions (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 25-30 
    Details
    ISSN: 0894-3230
    Keywords: 1,ω-bis(2-bromopyridinium)alkanes ; hydroxide ion ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction of OH- ion with 1,ω-bis(2-bromopyridinium)alkanes, where the reaction centers are separated by a varying number of methylene groups, was investigated to model the increased velocity of OH- attack on premicellar aggregated N-alkylpyridinium compounds. 1,ω-Bis(2-bromopyridinium)alkanes (RPBr) [R  =  propane (I), butane (II), pentane (III), hexane (IV) and octane (V)] were synthesized and characterized by standard procedures. The kinetics of I-V with OH- ion fitted two consecutive first-order reactions. The intermediate products, 1-(2-pyridone)-ω-(2-bromopyridinium)alkane, and also the final products 1,ω-bis(2-pyridone)alkanes, were isolated. Deuterium isotope effects, activation parameters and salt effects on the reaction rates suggest that OH- attack is rate limiting and there is a through-space acceleration of the initial attack due to the proximity of the positive charges. These results place an upper limit of 20-fold for the electrostatic acceleration in OH- attack in premicellar aggregates. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 237
    Electronic Resource
    Electronic Resource
    Kinetic study of the reactions of O-alkylisoureas with OH-acidic compoundsDedicated to Professor E. Vowinkel on the occasion of his 70th birthday. (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 47-53 
    Details
    ISSN: 0894-3230
    Keywords: N,N′-dicyclohexyl-O-(1-methylheptyl)isourea ; OH-acidic compounds ; acetic acid ; kinetics ; mechanisms ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Kinetic investigations on the reaction of N,N′-dicyclohexyl-O-(1-methylheptyl)isourea with acetic acid are described. The conversion proceeds partly through the intermediacy of a methylheptylcarbenium ion. However, in dilute solution an SN2 mechanism prevails. The results are discussed in terms of the simultaneous existence of two discrete mechanisms. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 238
    Electronic Resource
    Electronic Resource
    X-ray and NMR investigation of 25,27-dihydroxy-26,28-bis(diethoxyphosphoryloxy)-tert-butylcalix[4]arene in the 1,2-alternate conformation (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 63-70 
    Details
    ISSN: 0894-3230
    Keywords: calixarenes ; complexes ; conformation ; crystal structure ; 1H NMR ; 13C NMR ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal structure of 25,27-dihydroxy-26,28-bis(diethoxyphosphoryloxy)-tert-butylcalix[4]arene (1) (hexane solvate, 1:1) was determined by x-ray crystallography. The crystal data are P21/n, a  =  12.652(1) Å, b  =  12.564(2) Å, c  =  18.781(4) Å, β  =  105.56(1)°, V  =  2876.0(8) Å3, Z  =  2. In this complex the molecule adopts a 1,2-alternate conformation. Both the calixarene and hexane molecules are centrosymmetric. The phenol units in the asymmetric part of the calix are inclined with respect to the main macrocyclic plane by 115.46(6)° and 128.01(7)° for the phosphorylated and the non-phosphorylated ring, respectively. Self-inclusion of the ethyl chains in the half-cavities is observed. One intramolecular O - H…O and several intermolecular C - H…O hydrogen bonds are present. In the 1H NMR spectrum one average AX spin system for methylene bridge protons can be interpreted as fast (on the NMR time-scale) interconversion of non-phosphorylated phenol fragments. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 239
    Electronic Resource
    Electronic Resource
    Oxidation of allyl alcohol by alkaline periodate in the presence of micro amounts of palladium(II) (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 31-35 
    Details
    ISSN: 0894-3230
    Keywords: allyl alcohol ; oxidation ; alkaline periodate ; palladium(II) catalyst ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The oxidation of allyl alcohol by alkaline species of periodate, H2IO63-, was found to be catalysed by micro amounts of Pd(II) in 0.2 mol dm-3 alkali solution. The active species of the catalyst was found to be PdCl+. A mechanism involving the interaction of the catalyst and substrate in prior equilibria leading to the formation of a π-complex is proposed and the rate is derived. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 240
    Electronic Resource
    Electronic Resource
    Equilibrium acidities and homolytic bond dissociation enthalpies of m- and p-substituted benzaldoximes and phenyl methyl ketoximes (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 10-14 
    Details
    ISSN: 0894-3230
    Keywords: equilibrium acidities ; homolytic bond dissociation enthalpies ; benzaldoximes ; phenyl methyl ketoximes ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The equilibrium acidities in DMSO of nine p- and m-substituted benzaldoximes and eight p-substituted phenyl methyl ketoximes were measured. Estimates of the homolytic bond dissociation energies (BDEs) of the acidic O - H bonds in these compounds were made by combination of their pKHA values with the oxidation potentials of their conjugate bases, Eox(A-), using the equation BDE  =  1.37pKHA + 23.06Eox(A-) + 73.3 kcal (1 kcal  =  4.184 KJ). Plots of Eox(A-) vs pKHA for p-substituted benzaldoximes and p-substituted phenyl methyl ketoximes were linear with slopes near unity. Consequently, as required by the above equation, the BDEs estimated for the O - H bonds in these oximes were constant, being 88.3 ± 0.3 and 89.2 ± 0.4 kcal, respectively. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 241
    Electronic Resource
    Electronic Resource
    Lanthanide ion-induced hydrolyses of alkyl esters and amides of α-amino acidsFor a preliminary communication on the lanthanide-induced hydrolysis of peptides, see Ref. 1. (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 41-46 
    Details
    ISSN: 0894-3230
    Keywords: lanthanide ion ; hydrolysis ; α-amino acid esters ; α-amino acid amides ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Lanthanide ion-induced hydrolyses of methyl esters, ethyl esters, and amides of α-amino acids were systematically studied. In the hydrolysis of the alkyl esters, all the lanthanide ions are effective and the catalytic activities decrease in the order Ce(III), Nd(III) 〉 Sm(III) 〉 Eu(III) 〉 Gd(III), Ce(IV) 〉 Pr(III) 〉 Dy(III), Tb(III), Er(III), Ho(III), Tm(III) 〉 La(III), Lu(III), Yb(III). For the hydrolysis of the amides, however, the Ce(IV) ion is overwhelmingly more active than other lanthanide(III) and non-lanthanide ions. The results are interpreted in terms of the difference in the rate-limiting step for these two reactions. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 242
    Electronic Resource
    Electronic Resource
    Volumetric properties and compressibilities of alkyltrimethylammonium bromides and sodium alkylsulphates in aqueous solution (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 59-62 
    Details
    ISSN: 0894-3230
    Keywords: alkyltrimethylammonium bromides ; sodium alkylsulphates ; partial molar volumes ; partial molar isentropic compressibilities ; hydration ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Density and sound velocity data for aqueous solutions at 298.2 K containing alkyltrimethylammonium bromides and sodium alkylsulphates were analysed to yield partial molar volumes and isentropic compressions. The calculated contributions of methylene groups to the properties of alkyltrimethylammonium cations and alkylsulphate anions show no dependence on position in the alkyl chains and a common contribution to the ionic partial molar volumes over the range methyl ≤ n-octyl for the sulphates and n-propyl ≤ n-hexyl for the alkyltrimethylammonium ions. However, a switch in head group from trimethylammonium to sulphate changes the contribution of methylene groups to estimated partial molar isentropic compressibilities. The reasons for this sensitivity are discussed in terms of hydration characteristics. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 243
    Electronic Resource
    Electronic Resource
    Effects of oligooxyethylene linkage on intramolecular [2 + 2] photocycloaddition of styrene derivatives (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 79-83 
    Details
    ISSN: 0894-3230
    Keywords: [2 + 2] ; photocycloaddition ; quantum yield ; oligooxyehylene linkage ; cyclophane ; styrene derivatives ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: There are two possible explanations for the high yields in the intramolecular [2 + 2] photocycloaddition of compounds 3a-d in which two styrene moieties are bridged by an oligooxyethylene linkage: one is the electronic effects of phenoxy oxygen atoms at the para-position of the vinyl group and the other is the steric effects due to the flexibility of oligooxyethylene linkages. In order to clarify the contributions of the two effects, a study was made of the photoreaction of similar compounds in which oxygen atoms are present only at the ends of the chain, and therefore only the electronic effects are involved. In these compounds, the quantum yields of the photocycloaddition were found to be low. Hence the high yields in the photocycloaddition of 3a-d are concluded to be ascribable to the flexibility of oligooxyethylene linkages. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 244
    Electronic Resource
    Electronic Resource
    Crystallographic study and molecular orbital calculations of 1,2,5-thiadiazole 1,1-dioxide derivatives (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 91-100 
    Details
    ISSN: 0894-3230
    Keywords: 1,2,5-thiadiazole ; 1,1-dioxide derivatives ; single-crystal x-ray diffraction ; ab initio MO calculations ; structure ; conformation ; reactivity ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Single-crystal x-ray diffraction studies are reported for 3,4-dimethyl (I), 3-methyl-4-phenyl (II) and 3,4-diphenyl (III) derivatives of 1,2,5-thiadiazole 1,1-dioxide. Ab initio MO calculations on the electronic structure, conformation and reactivity of I, II and III are also reported and compared with the x-ray results. The structural data are related to previous kinetic and electrochemical experimental results on these compounds. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 245
    Electronic Resource
    Electronic Resource
    Stereodynamics of 4-substituted cyclohexenes. Formyl, vinyl and methyl substituents. Dynamic NMR and molecular mechanics studies (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 84-90 
    Details
    ISSN: 0894-3230
    Keywords: 4-formyl-, methyl- and -vinylcyclohexene ; stereodynamics ; conformation ; dynamic NMR ; molecular mechanics ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 1H and 13C{1H} NMR spectra of 4-formylcyclohexene in 50% CF2Cl2-50% CHF2Cl decoalesce at very low temperatures and, at 108 K, have sharpened into a major (77%) and a minor (23%) subspectrum. Based on the NMR spectra and molecular mechanics calculations, the major subspectrum is assigned to a family of equatorial conformations and the minor subspectrum to a family of axial conformations. The free energy of activation for conversion of the equatorial conformations to the axial forms is 5.6 kcal mol-1 (1 kcal  =  4.184 kJ) at 117 K. Within a family of conformations, interconversion occurs rapidly at 108 K via formyl group rotation. The conformational preference in 4-formylcyclohexene is solvent dependent. In 50% CF2Cl2-50% CHF2Cl, CHF2Cl and CF2Cl2, the respective ratios of equatorial to axial conformations are 77:23, 77:23, and 89:11 at 108 K. The 1H and 13C{1H} NMR spectra of 4-methylcyclohexene and 4-vinylcyclohexene in 50% CF2Cl2-50% CHF2Cl show no evidence of decoalescence at very low temperatures but do show differential broadening and subsequent sharpening of various resonances characteristic of exchange between strongly dominant equatorial conformations and axial conformations present at too low a concentration to be detectable by NMR. A lower limit on the free energy preference for the equatorial conformations is estimated to be 1.0 kcal mol-1. Molecular mechanics calculations also predict a stronger preference for equatorial conformations in 4-methylcyclohexene and 4-vinylcyclohexene than in 4-formylcyclohexene. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 246
    Electronic Resource
    Electronic Resource
    Are phosphatetrahedrane and diphosphatetrahedrane phosphorus or carbon bases? (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 678-683 
    Details
    ISSN: 0894-3230
    Keywords: phosphatetrahedrane ; diphosphatetrahedrane ; phosphorus bases ; carbon bases ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The protonation processes of phosphotetrahedrane (PTH) and diphosphatetrahedrane (DPTH) were studied using density functional theory approaches. The geometries of the neutrals and the protonated species were optimized at the B3LYP/6- 31G(d) level and the final energies were obtained using the B3LYP/6- 311+G(3df,2p) level of theory. Both PTH and DPTH are tetrahedral compounds which behave as carbon bases in the gas phase. In contrast with what was found for other phosphorus-containing cage structures such as tetraphosphacubane, the nature of the basic center does not change when the hydrogen atoms are substituted by bulky substituents. This is a consequence of the fact that both phosphorus and carbon protonation processes lead to C - P bond fission, so that the repulsive interactions between the susbtituents are not significantly different in carbon- or phosphorus-protonated structures. Protonation of DPTH at the P - P bond yields a local minimum with a P - H - P linkage similar to that described before for the most stable protonated form of P4. This seems to indicate that the existence of P - P linkages in strained structures clearly favors the formation of non-classical protonated species where the proton bridges the two phosphorus atoms. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 247
    Electronic Resource
    Electronic Resource
    Molecularly thin films of metallodendrimers (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 540-545 
    Details
    ISSN: 0894-3230
    Keywords: metallodendrimers ; molecularly thin films ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A non-covalent synthesis route to assemble metallodendrimers was extended to the fifth generation. Generation four (G4) was characterized by electrospray mass spectrometry. Thin films of generation five (G5) metallodendrimers were studied by tapping mode scanning force microscopy. Both on graphite and on mica spherical particles with a diameter of ca 15 nm were observed. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 248
    Electronic Resource
    Electronic Resource
    Improved Yukawa-Tsuno equation and the substituent effect on pyridine basicity (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 495-503 
    Details
    ISSN: 0894-3230
    Keywords: substituent effect ; Yukawa-Tsuno equation ; resonance demand ; pyridine basicity ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An improved Yukawa-Tsuno equation was obtained by inserting the resonance demand parameter r in the tetralinear extension of the Hammett equation constrained by a hyperbolic relation between meta and para substituent effects. The new equation with five adjustable parameters and other Yukawa-Tsuno models were applied to selected literature data for the ionization equilibria of 21 meta- and 20 para-substituted pyridinium ions in water at 25 °C. The data are best described by the new equation using either the sigma-benzoic acid scale with r = 1.35 ± 0.16 or a truncated sigma-plus scale (in which sigma-zero constants are assigned to 4-alkyl substituents) with r = 0.29 ± 0.04. Standard errors were estimated by Monte Carlo simulation. The results for the pyridinium ion demonstrate that the hyperconjugative effect by alkyl groups is inoperative and that through-resonance effects by electron-donating substituents are considerably hindered. The origin of this hindrance is ascribed to the particularities of nitrogen orbitals in heteroaromatic compounds. It is concluded that the pyridine reactivity lies between those of benzoic acid and benzylic cation, being much closer to the former. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 249
    Electronic Resource
    Electronic Resource
    Dipole moments of polyenic oligomeric systems. Part I. A one-dimensional molecular wire model (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 853-856 
    Details
    ISSN: 0894-3230
    Keywords: polyenic oligomerics ; dipole moments ; one-dimensional molecular wire model ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ground-state dipolar moments of oligomeric compounds, containing electron-donor (D) and electron-acceptor (A) groups as two terminal units of the polyenic bridge (D-wire-A), can well be described by means of a one-dimensional molecular wire model, which considers a scattering process of electrons through the charge-transfer conduction channel. The dipole moment of the oligomers (μn) follows a non-linear dependence of the polyenic bridge length (L) according to μn = μ0 + μ∞(1 - e- γL) where μ0 is the dipole moment of the first compound of the series, without a polyenic unit (n = 0), μ∞ is a limit value for L → ∞ and γ is the one-dimensional conduction constant of the π-molecular orbital channel of the molecular wire. This model can be extended to all those conjugated oligomers of the D-wire-A type where the electronic charge of the donor group can induce a soliton wave as far as through the polyenic bridge towards the acceptor group. Copyright © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 250
    Electronic Resource
    Electronic Resource
    Conformational effects on the mechanism of acid-catalyzed dehydration of hexitols (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 887-894 
    Details
    ISSN: 0894-3230
    Keywords: D-glucitol ; D-mannitol ; conformation ; dehydration reaction ; molecular mechanics ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Monte Carlo search of the low-energy regions of D-mannitol (4) and D-glucitol (5) conformational space was undertaken in order to investigate conformational effects on the stereochemistry of the acid-catalyzed dehydrative cyclization reaction of 4 and 5 to the corresponding 1,4:3,6-dianhydrohexitols. It was found that although dominant conformations in water resemble closely the crystal state conformations of 4 and 5, the same is not true in solvents of low polarity. The magnitudes of the calculated energies of the reactive conformations for the dehydrative cyclization reaction suggest an SN2 mechanism with a late transition state. Copyright © 1998 John Wiley & Sons, Ltd.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 251
    Electronic Resource
    Electronic Resource
    Structural and spectroscopic investigation of 1-amino-2,4-dinitrobenzenes (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 895-902 
    Details
    ISSN: 0894-3230
    Keywords: 1-amino-2,4-dinitrobenzenes ; structures ; single-crystal x-ray diffraction ; UV-visible spectrophotometry ; NMR spectroscopy ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal structures of 1-pyrrolidino-2,4-dinitrobenzene (3) and 1-morpholino-2,4-dinitrobenzene (4) were determined by single-crystal x-ray diffraction and the structures in solution were investigated by UV-visible spectrophotometry and 13C and 1H NMR spectrosccopy. Compound 4 crystallizes in the monoclinic space group P21/n with one independent molecule per asymmetric unit and 3 crystallizes in triclinic P-1 with three independent molecules per asymmetric unit. Rotation of the o-nitro group and of the amino group out of the aromatic plane was observed in both the solid state and in solution for both compounds. Copyright © 1998 John Wiley & Sons, Ltd.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 252
    Electronic Resource
    Electronic Resource
    Electrophilic aromatic substitutions: reactions of hydroxy- and methoxy-substituted benzenes with 4,6-dinitrobenzofuroxan: kinetics and mechanism (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 707-714 
    Details
    ISSN: 0894-3230
    Keywords: electrophilic aromatic substitutions ; 4,6-dinitrobenzofuroxan ; σ-complexation ; superelectrophile ; nitrobenzofuroxan ; kinetics of SEAr reaction ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rate constants have been determined in aqueous Me2SO mixtures for the reaction of super-electrophilic 4,6-dinitrobenzofuroxan (DNBF) with a series of hydroxy- and methoxy-substituted benzenes whose pKa values range between -3 and -9. The study extends the reactivity range of weakly basic aromatics with DNBF, from the family of indoles previously studied with pKa values ranging from -1 to -6. The overall rate constants for the reactions of DNBF as the electrophile are at least one order of magnitude greater than for the reactions of H3O+ with the same series of aromatics. This lends further credence to the notion that DNBF possesses super-electrophilic properties. An LFER is observed between logk50%Me2SODNBF and pKaH2O with slope 0.54. In the case of 1,3,5-trimethoxybenzene a significant kinetic isotope effect (KIE) is observed (kH/kD = 3.71 in 50% Me2SO). This system hence affords one of the few instances in which a KIE has been observed in SEAr reactions. It follows from the observed KIE that the addition of DNBF to the aromatic is not rate-limiting and that reversion to reactants and proton loss from the arenonium intermediate occur at comparable rates. Structures of the products of electrophilic substitution have been confirmed by 1H NMR. In all cases the regiochemistry of the reactions was identical to that observed in protonation studies of the starting aromatics. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 253
    Electronic Resource
    Electronic Resource
    Solvent dependence of pyranine fluorescence and UV-visible absorption spectra (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 743-750 
    Details
    ISSN: 0894-3230
    Keywords: pyranine ; photoacid ; solvent polarity parameters ; solvatochromism ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Fluorescence and UV-visible absorption spectra of HPTS (8-hydroxy-1,3,6-pyrenetrisulphonic acid trisodium salt, pyranine) were measured in a variety of solvents. Fluorescence maxima (in kcal mol-1) can be correlated with the Kosower Z parameter (r = 0.901), the Dimroth-Reichardt ET(30) parameter (r = 0.900) and the Winstein Y parameter (r = 0.916) using one-parameter fits. Good correlations (r = 0.98) were obtained for HPTS fluorescence in ethanol-water mixtures using the Y, YOTs and Z parameters. Fluorescence maxima of HPTS in aqueous sulphuric acid solutions gave an excellent correlation with YOTs (r = 0.991). Multi-parameter correlations, indicating the significance of specific solvent interactions, were also studied. In addition, fluorescence maxima correlate well with maximum/minimum ratios obtained from UV-visible absorption experiments. Results can be applied in the use of HPTS as a molecular probe of solvent environments and for extension of the YOTs scale in acidic solutions. HPTS is a unique molecular probe, not only because of its photoacidic properties and its widespread use as a pH-sensitive biosensor, but also because of its relative stability in acidic environments. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 254
    Electronic Resource
    Electronic Resource
    An ab initio study of 1-azabicyclo[1.1.0]butyl and isomeric cations (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 763-773 
    Details
    ISSN: 0894-3230
    Keywords: 1-azabicycl[1.1.0]butyl cations ; 3-azetidinyl cations ; aziridinylmethyl cations ; ab initio ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solvolysis products of 3-azetidinyl chlorides, tosylates, and mesylates have been interpreted previously to indicate that these reactions proceed by azabicyclo[1.1.0]butyl cationic intermediates. Whether these cations are formed by direct ionization to 3-azetidinyl cations followed by collapse to the bicyclic ion or are formed with anchimeric assistance by the lone pair of electrons on nitrogen is unclear. This investigation was initiated to assess the relative stability of these bicyclic cations and their isomeric 3-azetidinyl and aziridinylmethyl cations. All ab initio methods investigated suggest that the bicyclic ions (1) are much more stable than the corresponding 3-azetidinyl cations (3) and that transition states for conversion of the bicyclic ions to azetidinyl carbocations are not acheivable from the bicyclic ions. Hartree-Fock ab initio calculations on N-methyl (and N,2-dimethyl) bicyclic ions and their isomeric aziridinylmethyl cations (2) indicate that the bicyclic ions are significantly more stable than are the isomeric partially ring-opened cations, and that transition states (4) for conversion of the bicyclic ions to the corresponding aziridinylmethyl carbocations are probably energetically unattainable. Hartree-Fock theory predicts that the N-methyl-2-phenylbicyclic ions are slightly less stable than the resulting aziridinylmethyl cations. Calculations which include electron correlation (MP2) indicate, however, that all bicyclic ions investigated are more stable than any of their isomeric carbocations. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 255
    Electronic Resource
    Electronic Resource
    Kinetic and equilibrium studies of σ-adduct formation and substitution in the reactions of sulphite ions with some alkyl and aryl ethers and thioethers (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 787-792 
    Details
    ISSN: 0894-3230
    Keywords: nucleophilic aromatic substitution ; Meisenheimer complexes ; nucleophilic reactivity ; trinitro-aromatics ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Kinetic and equilibrium results are reported for the reactions of sulphite with the ethyl and phenyl ethers of 2,4,6-trinitrophenol and 2,4,6-trinitrothiophenol in 80/20 (v/v) water/DMSO. In each case 1:1 and 1:2 adducts are observed by reaction of sulphite at one or two unsubstituted ring positions respectively. In the case of the ethyl derivatives these adducts are long-lived however, the phenyl derivatives rapidly yield 2,4,6-trinitrobenzenesulphonate, the substitution product. This difference is attributed to a change in the nature of the rate-determining step, from nucleophilic attack with the phenyl derivatives to leaving group departure with the alkyl derivatives. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 256
    Electronic Resource
    Electronic Resource
    Kinetic and spectroscopic study of slow-binding inhibition processes in aldolaseDedicated to Keith Yates, former professor at the University of Toronto. (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 793-802 
    Details
    ISSN: 0894-3230
    Keywords: aldolase ; slow-binding inhibition ; enzyme affinity ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Compounds similar in structure to reactants, intermediates and products of the aldolase-catalysed reaction were synthesized and their affinities for the enzyme determined. The best situations were found with β-dicarbonyl phosphorylated compounds which are a good mimics of the incoming groups in the bond-forming process; the corresponding binding is characterized by slow-binding inhibition type, the inhibitors forming stabilized iminium ions and enamines with the enzyme; similar effects were obtained with an aromatic aldehyde, also capable of forming a stabilized iminium ion. The use of aldolase mutants allows one to characterize the lysyl group involved in the process and also to suggest a proton transfer mechanism for the iminium ion formation with the enzyme natural substrate. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 257
    Electronic Resource
    Electronic Resource
    Improved method for estimating the ZFS parameter D for delocalized biradicals (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 819-824 
    Details
    ISSN: 0894-3230
    Keywords: zero field splitting parameter, D ; organic biradicals ; triplets ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An ‘average’ approximation for calculating the zero-field splitting parameter, D, gives reasonable results when used to calculate D values for non-disjoint delocalized organic biradicals. When used to calculate disjoint localized organic biradicals the D values are approximately half the experimental values. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 258
    Electronic Resource
    Electronic Resource
    Correlation analysis of UV spectral data of some phenylhydrazones and semicarbazones by the dual-parameter equation. Observation of three types of behaviors of the λmax values induced by the polar effects of substituents (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 809-818 
    Details
    ISSN: 0894-3230
    Keywords: UV spectra ; dual-parameter equation ; correlation analysis ; polar effect ; spin-delocalization effect ; p-Y-substituted benzaldehyde phenylhydrazones ; p-Y-substituted benzaldehyde 2,4-dinitrophenylhydrazones ; p-Y-substituted benzaldehyde 4-nitrophenylhydrazones ; p-Y-substituted benzaldehyde N-phenylsemicarbazones ; p-Y-substituted benzaldehyde semicarbazones ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The K-band λmax values of the UV spectra of five types of p-Y-benzaldehyde derivatives, namely phenylhydrazones (1-Ys), 2,4-dinitrophenylhydrazones (2-Ys), 4-nitrophenylhydrazones (3-Ys), semicarbazones (4-Ys) and N-phenylsemicarbazones (5-Ys), were measured and the corresponding wavenumbers (νmax) calculated. Correlation analyses of the νmax values by the dual-parameter equation show that the νmax values of these compounds are affected, albeit to different degrees, by both spin-delocalization effects (σ·) and polar effects (σx) of the substituents. The spin-delocalization effects of substituents always facilitate bathochromic shifts of the λmax values (ρ· negative). However, polar effects of the substituents on these λmax data depend on the mode of polarization of these hydrazone or semicarbazone molecules, i.e. electron-pair acceptor substituents (Ys) facilitate bathochromic shifts for 1-Ys (ρx negative), but hypsochromic shifts for 2-Ys and 3-Ys (ρx positive), and induce very small shifts for 4-Ys and 5-Ys. As expected, donor Ys facilitate hypsochromic shifts for 1-Ys and bathochromic shifts for 2-Ys and 3-Ys and induce very small shifts for 4-Ys and 5-Ys. Possibly, a higher degree of polarization of the substrate molecule would demand a higher degree of polar assistance from the substituents at the transition states. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 259
    Electronic Resource
    Electronic Resource
    Ab initio molecular orbital study of the conformational energies (-ΔG° or A values) of 4-alkyltetrahydro-2H-thiopyrans (tetrahydrothiopyrans, thiacyclohexanes, thianes) (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 831-839 
    Details
    ISSN: 0894-3230
    Keywords: conformational energy ; tetrahydrothiopyrans ; ab initio molecular orbital ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ab initio 6-31G* and MP2/6-31G*//6-31G* methods were used to calculate the relative energies of the rotamers in the chair conformations of 4-alkyltetrahydro-2H-thiopyrans (tetrahydrothiopyrans, thiacyclohexanes, thianes; CH3, C2H5, i-C3H7, t-C4H9, neo-C5H11, SiMe3). The MP2/6-31G*//6-31G* conformational energies (-ΔG° or A values, kcal mol-1) of the 4-alkylthiacyclohexanes (Me = 1.94; Et = 1.72; i-Pr = 1.62; t-Bu = 5.49; neo-Pent = 1.39; SiMe3 = 2.76) are similar to those calculated for the corresponding alkylcyclohexanes. Plots of the calculated conformational energies for the 4-alkylthiacyclohexanes versus the calculated conformational energies for the corresponding alkylcyclohexanes are linear (slope = 1.01 and r = 0.999 for 6-31G* and slope = 1.09 and r = 0.990 for MP2/6-31G*//6-31G*). The conformational energies are strongly influenced by the magnitude and number of repulsive nonbonded hydrogen-hydrogen interactions and the gauche (synclinal) effects in the conformers. The carbon-sulfur bond lengths are mostly in the narrow range of 1.815-1.818 Å. The C - S - C angles vary from 97.1° to 99.4° and the C(3) - C(4) - C(7) angle in the most stable axial conformer is larger that the corresponding angle in its most stable equatorial conformer. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 260
    Electronic Resource
    Electronic Resource
    In vivo formation of C - S bonds in biotin. An example of radical chemistry under reducing conditions (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 529-535 
    Details
    ISSN: 0894-3230
    Keywords: biotin ; in vivo C - S bond formation ; radical chemistry ; reducing conditions ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The last step in the biosynthesis of biotin involves the formation of carbon-sulfur bonds at non-activated carbons catalyzed by biotin synthase. S-Adenosylmethionine (AdoMet) and an electron source are essential for activity in cell-free systems. This important finding connects biotin synthase to a family of enzymes, namely pyruvate-formate lyase, anaerobic ribonucleotide reductase and lysine 2,3-aminomutase, which use the same cofactors. Additional experimental data led to the proposition of the following general mechanism. The carbons to be functionalized are first activated by homolytic cleavage of the C - H bonds, initiated by the deoxyadenosyl radical produced by a monoelectronic reductive cleavage of AdoMet with NADPH as electron source. The electron transfer system involves flavoproteins and very likely the [Fe - S] center of biotin synthase. NADPH and the flavoproteins can be replaced by photoreduced deazaflavin. By using a deuterated substrate, a deuterium transfer into deoxyadenosine has been observed, indicating that biotin synthase should be closely related to lysine 2,3-aminomutase, which uses AdoMet as a surrogate of vitamin B12. The source of sulfur, the nature of the immediate sulfur donor and hence the mechanism of trapping of the intermediate radicals are still unknown. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 261
    Electronic Resource
    Electronic Resource
    Comparison of ΔG°Acid (gas phase) and kinetic acidities measured in methanolic sodium methoxide (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 614-617 
    Details
    ISSN: 0894-3230
    Keywords: ΔG°Acid (gas phase) ; kinetic acidities ; methanolic sodium methoxide ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Hydron exchange rates, kexc (M-1s-1), using methanolic sodium methoxide were compared with ΔG°Acid, (kcal mol-1) (gas phase) for 9-phenylfluorene, C6H5CH(CF3)2, m-CF3C6H4CH(CF3)2, p-CF3C6H4CHClCF3, m-CF3C6H4CHClCF3, 3,5-(CF3)2C6H3CHClCF3, fluorene and C6F5H. There is a good linear correlation for p-CF3C6H4CHClCF3, m-CF3C6H4CHClCF3 and 3,5-(CF3)2C6H3CHClCF3, with the others falling off the line. The fluorinated benzyl compounds and pentafluorobenzene have near-unity isotope effects and therefore differ from the fluorenyl compounds. Although the acidity and the exchange rates for three of the compounds [9-phenylfluorene, C6H5CH(CF3)2 and p-CF3C6H4CHClCF3] are similar, the important proton-transfer step to form a hydrogen-bonded carbanion intermediate and the subsequent breaking of that weak bond to form a free carbanion in methanol differ significantly for the fluoernyl compound compared with the two fluorinated benzylic compounds. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 262
    Electronic Resource
    Electronic Resource
    Chemistry of secologanin. Part 5. Graphical analysis of the acidic deglycosylation of vincoside derivatives (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 622-631 
    Details
    ISSN: 0894-3230
    Keywords: secologanin ; vincoside derivatives ; acidic deglycosylation ; graphical analysis ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Acidic hydrolysis and cyclization were studied in vincoside glycosides (‘natural’ series) and their dihydro derivatives (‘dihydro’ series) in which either one or both N atoms were free or blocked by an alkyl group. For interpretation of the results, a graph was constructed in which 25 points (actually circles) represent a maximum of 81 aglycone types and 40 arrows indicate 131 possible cyclizations. The reaction matrix of the graph was under thermodynamic control and in most cases afforded the thermodynamically most stable product aglycones. In addition to the deglycosylation, two types of cyclization were observed. In azacyclizations, the preferred nucleophilic site is N-4 over N-1, and the preferred electrophilic site is C-22 in the glycosides, C-21 over C-19 and C-17 in aglycones. In oxacyclizations, the preferred nucleophilic site is O-17 over C-18 and C-21, and the preferred electrophilic site is C-19 over C-21 and C-17 in the ‘natural’ series, C-21 over C-17 in the ‘dihydro’ series. In one case, the kinetically favoured aglycone types which had been generated in the reaction mixture were trapped in a subsequent reaction (outside the graph) before thermodynamic equilibrium was attained. With the help of graphical analysis it was possible to justify the formation of the most favourable and actually isolated products and pathways out of a large number of possibilities. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 263
    Electronic Resource
    Electronic Resource
    New DNA-binding ruthenium(II) complexes as photo-reagents for mononucleotides and DNA (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 577-583 
    Details
    ISSN: 0894-3230
    Keywords: DNA binding agents ; ruthenium(II) complexes ; photoreagents ; DNA ; mononucleotides ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The spectroscopic properties of two photoprobes for DNA, Ru(phen)2(PHEHAT)2+ and Ru(TAP)2(PHEHAT)2+ (phen = 1,10-phenanthroline, TAP = 1,4,5,8-tetraazaphenanthrene, PHEHAT = 1,10-phenanthrolino[5,6-b]-1,4,5,8,9,12-hexaazatriphenylene), were examined and compared with those of complexes containing either an extended planar ligand (DPPZ) or π-acceptor ligands. The orbitals involved in the absorption and emission processes for Ru(phen)2(PHEHAT)2+ imply the PHEHAT ligand, whereas the chromophore and luminophore for Ru(TAP)2(PHEHAT)2+ are associated with the Ru(II) → TAP MLCT transition. The two complexes exhibit completely different behaviour in the presence of DNA. Whereas Ru(phen)2(PHEHAT)2+, which does not emit in water, luminesces upon intercalation between the DNA base pairs, the luminescence of Ru(TAP)2(PHEHAT)2+ is quenched by binding to DNA. Emission quenching is also observed in the presence of GMP, with a quenching rate constant of 1.25 × 109 l mol-1 s-1. This strongly suggests the presence of a photo-induced electron transfer from the guanine residues of GMP or DNA to the excited complex and leads to the conclusion that this complex is a good DNA photoreagent. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 264
    Electronic Resource
    Electronic Resource
    Absolute proton affinities of some substituted toluenes: the additivity rule of thumb for ipso attack (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 663-669 
    Details
    ISSN: 0894-3230
    Keywords: ipso proton affinities ; additivity ; disubstituted toluenes ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The problem of the ipso protonation of toluene and its predominantly disubstituted derivatives was considered by the MP2(fc)/6-31G**//HF/6-31G*+ZPE(HF/6-31G*) theoretical model. The substituents involved covered a wide range of different donor-acceptor capabilities. It is shown that the calculated MP2 ipso proton affinities of substituted toluenes follow mutatis mutandis the same additivity rule which was found earlier to be operative in polysubstituted benzenes, naphthalenes and biphenylenes. The additivity equation is both intuitively appealing and useful, being able to offer quantitative estimates of the proton affinity by very simple calculation. It is based on the concept of the increment, which in turn describes the influence of a single substituent on the proton affinity. Any substituent behaves as a rule as if the other were non-existent, thus giving rise to the independent substituent approximation (ISA). The performance of the additivity rule of thumb is very good, as evidenced by the average absolute deviation of 1 kcal mol-1. Larger deviations are possible, but they rarely occur, being indicative of a difference in interactions between substituents in the initial neutral base and in the final cationic conjugate acid. Finally, it follows as a corollary of the present analysis that protonation ipso to the CH3 group is never thermodynamically the most favourable site of proton attack in the benzene ring, provided that there is a single unsubstituted carbon atom within the aromatic moiety. The relevance of ipso protonation in persubstituted benzenes is briefly discussed. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 265
    Electronic Resource
    Electronic Resource
    Photoinduced electron transfer and strand cleavage in pyrenyl-DNA complexes and adducts (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 561-565 
    Details
    ISSN: 0894-3230
    Keywords: pyrenyl-DNA complexes and adducts ; photoinduced electron transfer ; strand cleavage ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The fluorescence of pyrenyl residues in complexes with the nucleic acid bases G, C and T, but not A, is strongly quenched by photoinduced electron transfer mechanisms. Site-specifically modified 11-mer oligonucleotide duplexes containing a single modified guanosyl base G* bearing a covalently attached pyrenyl residue were prepared in order to probe for photochemical damage associated with these photoinduced electron transfer reactions. When the pyrenyl residue positioned at G* is photoexcited with 355 nm light, direct strand cleavage is observed at that site with low quantum yield. Frank strand breaks are also observed up to five base pairs away from G*, suggesting that intrastrand migration of a reactive intermediate from base to base is occurring. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 266
    Electronic Resource
    Electronic Resource
    Genetic engineering approaches to enzyme design and mechanism (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 536-539 
    Details
    ISSN: 0894-3230
    Keywords: enzyme design ; enzyme mechanism ; genetic engineering ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Aspartate aminotransferase (AATase) and aminocyclopropane carboxylate synthase (ACC synthase) are pyridoxal phosphate (PLP)-dependent enzymes whose common junction of mechanistic divergence is after the formation of a Cα carbanion from the amino acid substrate bound to PLP as a Schiff base (aldimine). AATase catalyzes the reversible interconversion of α-amino acids and α-keto acids, while ACC synthase effects the irreversible decomposition of S-adenosylmethionine (SAM) to 1-aminocyclopropane-1-carboxylate (ACC) and 5′-methylthioadenosine (MTA). ACC is subsequently converted to ethylene, the plant ripening and senescence hormone, by ACC oxidase, the next enzyme in the pathway. AATase and ACC synthase exhibit many similar phenomenological characteristics that result from different detailed mechanistic origins. The kcat/KM versus pH profiles for both enzymes are similar (AATase, acidic pKa = 6.9, basic pKa = 9.6; ACC synthase, acidic pKa = 7.5, basic pKa = 8.9); however the acidic pKa of AATase reflects the ionization of an enzyme proton from the internal Schiff base, and the basic one is that of the α-amino group of the substrate, while the opposite situation obtains for ACC synthase, i.e. the apparent pKa of 7.4 is due to the α-amino group of SAM, whereas that of 9 reflects the Schiff base pKa. The mechanistic imperative underlying this reversal is dictated by the reaction mechanism and the low pKa of the α-amino group of SAM. The low pKa of SAM requires that the enzyme pKa be moved upward in order to have sufficient quantities of the reacting species at neutral pH. It is shown by viscosity variation experiments with wild-type and active site mutant controls of both enzymes that the reaction of SAM with ACC synthase is 100% diffusion controlled (kcat/KM = 1.2 × 106 l mol-1 s-1) while the corresponding reaction for the combination of L-aspartate with AATase is insensitive to viscosity, and is therefore chemically not diffusion limited. Tyr225 (AATase) or Tyr233 (ACC synthase) forms a hydrogen bond with the PLP in both enzymes, but that formed with the former enzyme is stronger and accounts for the lower pKa of the Schiff base. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 267
    Electronic Resource
    Electronic Resource
    Aromaticity of pericyclic reaction transition structures: magnetic evidence (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 655-662 
    Details
    ISSN: 0894-3230
    Keywords: pericyclic reaction transition structures ; aromaticity ; magnetic susceptibility ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The transition states of thermally allowed pericyclic reactions are aromatic. They not only have highly delocalized structures and large resonance stabilizations (energies of concert), but also strongly enhanced magnetic susceptibilities (Λ) and appreciable NICS (nucleus-independent chemical shifts) values arising from the diatropic ring currents. Aromaticity is the consequence of cyclic electron delocalization, which can have σ and hybrid, and not just π character. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 268
    Electronic Resource
    Electronic Resource
    Intermediates in organometallic and organic chemistry: spectroscopy, polymers, hydrogenation and supercritical fluids (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 589-596 
    Details
    ISSN: 0894-3230
    Keywords: intermediates ; spectroscopy ; polymers ; hydrogenation ; supercritical fluids ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: IR spectroscopy has transformed the study of mechanistic organometallic chemistry. Reaction intermediates can now be detected and characterized; their kinetics can be measured and their behaviour understood. However, the field is not static. New techniques are still being developed. We focus here on hydrogenation and related reactions describing (i) a miniature low-temperature/high-pressure cell, which allows photochemical reactions to be studied under high pressures of gases, (ii) the use of flow reactors for continuous reactions in supercritical fluids, including hydrogenation of organic compounds, and (iii) the use of supercritical fluid solutions for studying weak metal-ligand interactions by nanosecond time-resolved IR spectroscopy (TRIR) and the application of TRIR to the detection of intermediates in organic reactions. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 269
    Electronic Resource
    Electronic Resource
    Kinetics of the hydrolysis of cyclic N-substituted sulfamides: 4-amino-2-cyclohexyl- and 4-amino-2-phenethyl-2,3-dihydro-3-oxo-1,2,5-thiadiazole 1,1-dioxides (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 489-494 
    Details
    ISSN: 0894-3230
    Keywords: Cyclic N-substituted sulfonamides ; 1,2,5-thiadiazole 1,1-dioxide derivatives ; hydrolysis ; kinetics ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The hydrolysis reactions of 4-amino-2-phenethyl- and 4-amino-2-cyclohexyl-2,3-dihydro-3-oxo-1,2,5-thiadiazole 1,1-dioxide (Ia and Ib) were investigated in the range 24-73 °C in buffered aqueous solutions. The observed rate constants (kobs) are independent of pH in the range ca 1-4 pH, but increase with increase in pH above ca 4. A linear log kobs vs pH profile with unit slope is observed from pH ca 4 up to the highest experimental pH (ca 10). The products are the corresponding new compounds: 2-amino-2-[(N-substituted-sulfamoyl)imino]acetic acid salts. The C=N bond of these compounds hydrolyses further, in a slow reaction, to the sulfamide and oxalic acid derivatives. The substrates decompose to the final products without accumulation of the acetic acid derivatives under these experimental conditions. A mechanism is proposed. Rate constants and activation parameters are given for the first reaction step. Owing to steric effects, the reaction rate is higher for the N-phenethyl-substituted derivative than for the 2-cyclohexyl-substituted derivative. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 270
    Electronic Resource
    Electronic Resource
    Improved method of calculating group polarization effects: constants σα (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 485-488 
    Details
    ISSN: 0894-3230
    Keywords: group polarization effects ; polarizability countants ; ab initio ; Sadlej's basis set ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An improved model is presented for ab initio calculations of the polarizability constants σα using Sadlej's basis set. A new set of constants was calculated for common groups and these were compared with previous 3-21G and 3-21G* calculations and with some experimental equilibrium constants in the gas phase. For the time being, the calculations seem to be the most general approach for obtaining these constants whereas the experimental possibilities are limited in scope. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 271
    Electronic Resource
    Electronic Resource
    Rate enhancement of 1,3-dipolar cycloaddition of N-methylindole: the singular role of Grignard reagents (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 455-466 
    Details
    ISSN: 0894-3230
    Keywords: 1,3-dipolar cycloaddition ; N-methylindole ; Grignard reagents ; rate enhancement ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactions of 2-N-methylindolyl and 2- and 3-benzo[b]thiophenyl anions with nitrile oxides and nitrilimines were performed in order to investigate whether the use of anionic dipolarophiles modifies a classical 1,3-dipolar cycloaddition. When lithium compounds were used as bases, the heterocyclic anions invariably acted as nucleophilic species; in contrast, when a Grignard reagent was employed, the N-methylindole gave cycloaddition products with an extraordinary rate enhancement. The hypothesis that N-methylindole and ethylmagnesium bromide give an adduct much more reactive than N-methylindole itself was supported by the results of a theoretical investigation. The structure and electron distribution of the adduct were determined by ab initio calculations and compared with those of known Grignard complexes with nitrogen ligands. The performance of different basis sets was tested. The quantum theory of atoms in molecules was used to determine atomic charges and to describe the nature of bonds in terms of the properties of the electron density at the bond critical points. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 272
    Electronic Resource
    Electronic Resource
    1:1 Crystal complex of 2′,6′-dimethoxyflavone and 2,6-dimethoxybenzoic acid. Relationship of pKa to x-ray hydrogen bond data (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 751-755 
    Details
    ISSN: 0894-3230
    Keywords: 2′,6′-dimethoxyflavone-2,6-dimethoxybenzoic acid complex ; crystal structure ; pKa values ; hydrogen bonds ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystal structure of the 2′,6′-dimethoxyflavone-2,6-dimethoxybenzoic acid complex was determined. Owing steric hindrance of the methoxy groups, the two H-bonded molecules are twisted. Earlier results were used to establish a relationship between the pKa values of different acids and their hydrogen bond distances in complexes with 2′,6′-dimethoxyflavone. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 273
    Electronic Resource
    Electronic Resource
    The ring inversion of silacycloheptatriene and cycloheptatriene. Comparison of the ‘aromaticity’ of planar and boat conformers estimated by nucleus-independent chemical shift (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 475-477 
    Details
    ISSN: 0894-3230
    Keywords: cycloheptatriene ; silacycloheptatriene ; ring inversion ; aromaticity ; ab initio calculation ; nucleus-independent chemical shift ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nucleus-independent chemical shifts (NICS) of boat and planar structure of silepins (1) and cycloheptatriene (2) were calculated at the HF/6-31+G* level for the Becke3LYP/6-31G* optimized geometries in order to investigate the correlation between the inversion barrier and aromatic nature in the boat and planar forms of 1 and 2. The NICS of unsubstituted silepin 1a indicated that there is almost no stabilization in the boat form (NICS, -0.5) and that the planar form (NICS, 3.5) is relatively destabilized in comparison with the boat form. On the other hand, the NICS of 2 showed that there is considerable homoconjugative stabilization in the boat form (NICS, -4.2) and destabilization in the planar form (NICS, 8.2). In addition to the geometrical effects resulting from angle strain, these electronic effects are considered to affect the energy barriers for ring inversion, which have been calculated to be 0.9 kcal mol-1 for 1a and 5.2 kcal mol-1 for 2. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 274
    Electronic Resource
    Electronic Resource
    Complexation of basic amino acids by water-soluble calixarene sulphonates as a study of the possiblemechanisms of recognition of calixarene sulphonates by proteins (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 693-696 
    Details
    ISSN: 0894-3230
    Keywords: calixarene sulphonates ; amino acids ; proteins ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The interactions of calixarene sulphonates with the basic amino acids arginine and lysine were studied by 1H NMR spectroscopy. Strong electrostatic binding occurs for calix[4]arene sulphonate with both lysine and arginine at pH 1 and 5. For the higher calixarenes, only weak interactions at the faces of the flattened macrocycles occur. This binding is in contrast to the inhibition of protein-protein interactions by the calixarenes where the calix[6]arene and calix[8]arene sulphonates show much stronger effects. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 275
    Electronic Resource
    Electronic Resource
    Kinetics and mechanism of cerium(IV) oxidation of primary and secondary alcohols catalysed by chromium(III) (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 697-700 
    Details
    ISSN: 0894-3230
    Keywords: Primary alcohols ; secondary alcohols ; oxidation ; cerium (IV) ; chromium(III) catalysis ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The cerium(IV) oxidation of isobutanol, isoamyl alcohol isopropyl alcohol, and secondary butanol catalysed by chromium(III) was studied in sulphuric and perchloric acid mixture at 30 °C. The reaction was found to proceed with the formation of a chromium(IV) intermediate followed by its complexation with alcohol. The complex thus formed decomposed into an aldehyde or ketone by a two-electron hydride ion transfer. The formation constants for complexes were determined from Michaelis-Menten plots. The accelerating effect of [H+] on the reaction is attributed to the formation of active species, HCe(SO4)3- and HAlcohol+, of the oxidant and alcohol, respectively. The activation parameters were also determined and an isokinetic plot was found to be linear. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 276
    Electronic Resource
    Electronic Resource
    Cyclizations in the homolytic reactions of unsaturated nitriles with tert-butylmercury halides in the presence of proton donorsElectron Transfer Processes. Part 65. (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 715-721 
    Details
    ISSN: 0894-3230
    Keywords: unsaturated nitriles ; homolytic reactions ; cyclization ; tert-butylmercury halides ; proton donors ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cyclizations are observed in the homolytic reactions of t-BuHgI with CH2=CHCH2YCH2CN [Y = CH2, O, CMe2, C(CO2Et)2, NCH2CN] and CH2=CHCH2CH2YCH2CN [Y = CH2, O, C(CO2Et)2] in Me2SO in the presence of hydriodic acid. Only with Y = C(CO2Et)2 does the adduct radical, t-BuCH2ĊHCH2YCH2CN, undergo facile 5-exo cyclization in the absence of a proton donor. The other 5-exo and all 6-exo cyclizations require substrate protonation to yield t-BuCH2ĊH(CH2)nYCH2C≡NH+ (n = 1, 2), which cyclizes readily to the iminium radical cation followed by electron transfer with I- or t-BuHgI2- to form the imine as a precursor to the cyclopentanone or cyclohexanone upon hydrolysis. For CH2=CHCH2C(CO2Et)2CH2CN the formation of the cyclopentanone is dramatically promoted by NH4I in the dark in the absence of any other acid. In this case, where cyclization of the adduct radical occurs readily without substrate activation, protonation of the cyclized iminyl radical allows the electron transfer with I- or t-BuHgI2- to occur with regeneration of t-Buċ. A similar effect is observed with CH2=CHCH2C(CO2Et)2CH2N3 where only a slow reaction is observed upon photolysis with t-BuHgI in the absence of NH4I, although apparently cyclization of t-BuCH2ĊHCH2C(CO2Et)2CH2N3 (with loss of N2) occurs readily. In the presence of NH4I the cyclized aminyl radical can be protonated and the resulting amine radical cation readily reduced by I- or t-BuHgI2- to continue a chain process. With the thioesters CH2=CHCH2YCH2C(O)SPh [Y = O, CH2, CMe2, C(CO2Et)2], significant cyclization upon photolysis with t-BuHgX occurred only for Y = C(CO2Et)2. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 277
    Electronic Resource
    Electronic Resource
    Hydrogen-bonding-based thermochromic phenol-amine complexes (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 737-742 
    Details
    ISSN: 0894-3230
    Keywords: thermochromism ; proton transfer ; hydrogen bond ; phenol ; amine ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Variable-temperature UV-vis, 13C NMR and IR studies showed that proton-transferred complexes were formed between phenols and amines in apolar solvents at low temperature. Upon cooling a solution of p-nitrophenol and diisopropylamine in toluene, the colour of the solution changed from colourless to yellow. This thermochromism was ascribed to the proton transfer in the hydrogen-bonding complex. Under UV-vis conditions, butylamine and imidazole also caused similar thermochromism upon complexation with p-nitrophenol, while triethylamine, quinuclidine and pyridine did not. The thermochromic behaviour was particularly dependent on the stoichiometry of the amine and the phenol: a solution of 3,3′-dibromo-5,5′-dinitro-2,2′-biphenyldiol and diisopropylamine with a molar ratio of 1:1 showed no thermochromism, while solutions with 1:2 or higher ratios showed thermochromism, indicating that excess amine is required to obtain the proton-transferred species. These results revealed that the proton-transferred species forms in apolar solvents at low temperature if an appropriate hydrogen-bonding network between the phenol and the amine can stabilize it. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 278
    Electronic Resource
    Electronic Resource
    Reaction of phenyllithium with E-cinnamaldehyde: survey of several variables and their influence on the mechanism of reaction and in organic synthesis (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 722-730 
    Details
    ISSN: 0894-3230
    Keywords: phenyllithium ; E-cinnamaldehyde ; organolithium ; addition ; mechanism ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction of phenyllithium (PhLi) with E-cinnamaldehyde (1) has been fully examined. Besides the main product E-1,3-diphenyl-2-propen-1-ol (2), three other by-products were detected: E-cinnamyl alcohol (3), E-chalcone (4) and E-1,3-diphenylpropanone (5). The effect of several variables on the nature and relative yields of products was examined. In all the solvents studied, the selectivity of the reaction was higher at higher temperatures, probably owing to aggregation effects; at lower temperatures the reaction is slower and the amount of by-products increases. The addition is complete in 1 h at 0 °C in THF for a [PhLi]:[1] ratio of 1:1, and longer reaction times have almost no effect, while for the reaction in toluene the amount of by-products increases when the reaction mixture is allowed to stand. The concentration of the reagents has no important effect on the reaction as long as the ratio is kept equal to 1:1. The influence of light was examined and a marked decrease in the selectivity of the reaction was observed. When the reaction was carried out in the presence of radical traps, no by-products were detected. Finally, for a [PhLi]:[1] ratio of 3:1 the main product is the dihydrochalcone 5, especially for long reaction times. All the above results could be interpreted in a reaction scheme involving electron transfer from PhLi to 1, and further reaction of the radical ions formed as well as reaction of dimeric PhLi without previous deaggregation when the ratio is 3:1.­© 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 279
    Electronic Resource
    Electronic Resource
    Stability and nitrosation efficiency of substituted N-methyl-N-nitrosobenzenesulfonamides (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 756-760 
    Details
    ISSN: 0894-3230
    Keywords: N-methyl-N-nitrosobenzenesulfonamides ; stability ; nitrosation efficiency ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of substituted N-methyl-N-nitrosobenzenesulfonamides [2,4,6-(CH3)3, 4-CH3O, 4-CH3, 4-Cl and 4-NO2] were synthesized. All of them transfer their nitroso group to N-methylaniline in a quantitative manner, the more reactive being those substituted with electron-withdrawing groups, thus resembling some of the known alkyl nitrites. Studies of their acid denitrosation and base-catalysed hydrolysis demonstrated that the nitrosobenzenesulfonamides are fairly stable in aqueous media between pH 2 and 11. Their relative stability in aqueous media together with their ability to transfer the nitroso group to nucleophiles suggest their use as excellent alternatives to alkyl nitrites in both neutral and basic media. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 280
    Electronic Resource
    Electronic Resource
    Conformational analysis of substituted 5,6,7,8-tetrahydrodibenzo[a,c]cyclo-octene: comparison of 1H NMR, molecular mechanics and semiempirical methods (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 781-786 
    Details
    ISSN: 0894-3230
    Keywords: eight membered rings ; conformational analysis ; molecular mechanics ; semiempirical methods ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 6-Mono- and trans-6,7-di-substituted derivatives of 5,6,7,8-tetrahydrodibenzo[a,c]cyclo-octene exist in solution in two different conformations. The experimental ΔGo values obtained from 1H NMR spectra are compared with the ΔEsteric and ΔG values calculated by molecular mechanics and semiempirical quantum mechanics methods respectively. The experimental ΔGo values are reproduced better by the ΔEsteric values. The semiempirical methods predict the order of stability of the conformers correctly except for two cases in the PM3 and AM1 methods, but the estimated values are far from the experimental ones. The standard deviation between the experimental ΔGo values and those calculated by semiempirical methods is less for AM1 and MNDO and greater for PM3 and MINDO/3. The conformational space of the flexible side chains in monoacetoxy 1d, monohydroxy 1e, trans-diacid 2d, trans-dimethyl ester 2e and trans-bis-hydroxymethyl 2f searched by molecular mechanics is not reproduced completely by semiempirical methods. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 281
    Electronic Resource
    Electronic Resource
    Double fragmentation in cation radicals. An example in the NADH analogues series (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 774-780 
    Details
    ISSN: 0894-3230
    Keywords: double fragmentation ; cation radicals ; NADH analogues ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The cation radical of 9-tert-butyl-N-methylacridan, generated electrochemically or photochemically, offers, in the presence of strong bases, a remarkable example of a double fragmentation. Whereas in acidic or weakly basic media the tert-butyl radical is cleaved with concomitant formation of the methylacridinium cation, the presence of a strong base triggers the cleavage of both the methyl group borne by the nitrogen atom and the tert-butyl group on C-9 leading to acridine, formaldehyde and the tert-butyl anion, even though methylacridinium cation is stable under these conditions. The origin of this unprecedented behavior resides in the prior deprotonation of the methyl group borne by the nitrogen atom which outruns the usual deprotonation at the 9-carbon because this is slowed by the steric hindrance due to the presence of the tert-butyl group. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 282
    Electronic Resource
    Electronic Resource
    Effect of sulfuric acid on reactions of peroxymonosulfate ion with sulfides and thiol esters (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 803-808 
    Details
    ISSN: 0894-3230
    Keywords: peroxymonosulfate ion ; oxidation ; sulfuric acid ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Peroxymonosulfate ion, HSO5-, as Oxone in aqueous H2SO4, oxidizes sulfides [MeSC6H4X(p), X = Me, H, NO2] to sulfoxides and converts aryl thiobenzoates [PhCOSC6H4X(p), X = Me, H] and thiol phosphorus(V) esters [Ph2POSPh, (EtO)2POSPh, Ph2POSEt, Ph(EtO)POSEt] into the acids and sulfonate ions. Second-order rate constants increase with increasing concentration of H2SO4 (10-53 wt%), owing to the high polarity of the medium rather than to acid catalysis. The rate increases fit the Grunwald-Winstein equation based on YOTs solvent parameters derived from rate effects on SN1 solvolyses. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 283
    Electronic Resource
    Electronic Resource
    Cation radical cycloaddition polymerization: Diels-Alder copolymerization (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 825-830 
    Details
    ISSN: 0894-3230
    Keywords: cation radical cycloaddition polymerization ; Diels-Alder copolymerization ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Diels-Alder cycloaddition copolymerization of a bis(diene) with ionizable bis(dienophiles) via a cation radical mechanism has been accomplished using tris(4-bromophenyl)aminium hexachloroantimonate as a catalyst in dichloromethane solvent. The reactions occur at 0°C and yield Diels-Alder polymers of MW up to ca. 10,000 and a polydispersity index ca. 2. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 284
    Electronic Resource
    Electronic Resource
    Effect of solvent composition on the acidity of phenols in dimethyl sulfoxide-water mixtures (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 847-852 
    Details
    ISSN: 0894-3230
    Keywords: phenols ; acidity ; solvent composition ; supersolvent ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of solvent composition on the acidity of substituted phenols in DMSO-H2O systems was examined. It is shown that in DMSO-H2O mixtures with up to 35 mol% DMSO there is a linear relationship between the pKa values of monosubstituted phenols in the binary solvent mixtures of different compositions and the corresponding pKa values in water. This leads to an equation relating the slope and intercept terms, pKa(DMSO-H2O) = slope[pKa(H2O)] + intercept. The basis of this relationship in the Kirkwood-Westheimer equation is examined. The significance of a possible ‘supersolvent’ is discussed. The applicability of the relationships derived herein to other rate-equilibria relationships and solvent mixtures is considered. Copyright © 1998 John Wiley & Sons, Ltd.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 285
    Electronic Resource
    Electronic Resource
    Convenient criterion for the distinction between electrophilic and electron transfer reactions of electron-rich alkenes (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 15-24 
    Details
    ISSN: 0894-3230
    Keywords: electrophilic reactions ; electron transfer reactions ; electron-rich alkenes ; tetracyanoethylene ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Both experimental and theoretical studies confirm that the formation of aryl vinyl ether and aryl vinyl sulfide cation radicals from the corresponding neutral substrates correlates with the Brown σ+ parameters as opposed to Hammett σ values. Peak oxidation potentials for both classes of substrates correlate preferentially with σ+, as do gas-phase ionization energies calculated by both semi-empirical and ab initio methods. In contrast, the protonation energies of the same substrates, which relate to carbocation formation, correlate preferentially with σ values, as do rates of protonation and other electrophilic additions. These observations permit a sharp distinction between electrophilic and electron transfer reactions of these two common classes of electron-rich substrates. Using this criterion, the cycloadditions of tetracyanoethylene to these substrates are found to proceed via an electrophilic mechanism, rather than by a previously proposed electron transfer mechanism. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 286
    Electronic Resource
    Electronic Resource
    Radical bromination of 1,1- and 1,2-diphenylethylenes in 1,2-dichloroethaneDedicated to the memory of Professor Giuseppe Bellucci (dièd 3 March 1996). (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 685-692 
    Details
    ISSN: 0894-3230
    Keywords: radical bromination ; diphenylethylenes ; 1,2-dichloroethane ; caged radical intermediates ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The radical bromination of 1,1- and 1,2-diphenylethylenes in 1,2-dichloroethane was investigated on the basis of kinetic and product distribution data. Whereas the ionic process followed a third-order rate law (second order in Br2), the radical bromination was second order in Br2 and zero order in olefin in the reagent concentration range examined. Significant inverse kinetic isotope effects were found for the bromination of 3,4′-bis(trifluoromethyl)-1,1-diphenylethylene and cis-1,2-diphenylethylene under these conditions. At variance with the ionic bromination, which gave mixtures of meso- and d,l-dibromides only the meso-dibromides were obtained both from the cis- and trans-1,2-diphenylethylenes. The kinetic and product distribution data for the radical process are discussed in terms of a mechanism in which caged radical intermediates are formed. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 287
    Electronic Resource
    Electronic Resource
    Kinetic mechanism for dimerization of an α-thioamide substituted benzyl carbocation in aqueous solution (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 701-706 
    Details
    ISSN: 0894-3230
    Keywords: carbocation ; thioamide ; kinetics ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The products of reaction of the α-(N,N-dimethylthiocarbamoyl)-4-methoxybenzyl carbocation (1+) intermediate of solvolysis of α-(N,N-dimethylthiocarbamoyl)-4-methoxybenzyl benzoate esters (1-O2CAr) show a strong dependence on solvent. The only product from reaction in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) is 2-dimethylamino-6-methoxybenzothiophene (2) from intramolecular cyclization of 1+. The reaction of 1+ in 50:50 (v/v) methanol-water (I = 0.50, NaClO4) gives mainly the adducts to solvent. In 50:50 (v/v) trifluoroethanol-water (I = 0.50, NaClO4), 1+ partitions between reaction with solvent (ks, 27% yield), cyclization to form 2 (kc, 3% yield) and nucleophilic addition of 2 to 1+ (kalk, 70% yield) to form dimeric product 3. The yield of 3 in 50:50 (v/v) trifluoroethanol-water (I = 0.50, NaClO4) is independent of the leaving group at 1-O2CAr and remains constant as the concentration of the substrate is increased fourfold. These data show that the rate-determining step for dimerization of 1-O2CAr is ionization of substrate to form 1+ and that the products of the reaction are determined by the rate constant ratio for partitioning of 1+ between addition of solvent and cyclization. The rate constant ratios determined for the partitioning of 1+ in 50:50 (v/v) trifluoroethanol-water (I = 0.50, NaClO4) were ks/kc = 0.8 M-1 and kalk/ks = 540 000 M-1. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 288
    Electronic Resource
    Electronic Resource
    Substituent effects on the electrochemical oxidation of N,N′,N″-triphenyl-1,3,5-triaminobenzenes (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 731-736 
    Details
    ISSN: 0894-3230
    Keywords: substituted 1,3,5-triaminobenzenes ; electrochemistry ; linear free energy correlation ; substituted triphenylamines ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Correlation analysis of the oxidation potentials of a series of N,N′,N″-triphenyl-1,3,5-triaminobenzenes (TPABs) substituted at the para positions of the outer phenyl rings shows a linear free energy relationship with resonance-enhanced substituent parameters (σ+). Reaction parameters (ρ+) for oxidation of TPABs were found to be -1.53, -1.45 and -1.34 (per substituent) in methylene chloride, acetonitrile and propylene carbonate respectively. The resonance enhancement and small magnitude of the ρ+ values are related to a significant but weak delocalization of charge onto the outer phenyl rings in the molecular orbitals of radical cations resulting from the oxidation of TPABs. Data on the oxidation of p-substituted triphenylamines were treated similarly and gave a ρ+ value of -3.27 (per substituent) in acetonitrile, greater than that for TPABs owing to a more significant delocalization of charge onto the phenyl rings in the molecular orbitals of the corresponding radical cations. To demonstrate their predictive value, these linear free energy correlations were used to estimate the oxidation potentials of similarly substituted N,N,N′,N′,N″,N″-hexaphenyl-1,3,5-triaminobenzenes, which are of interest as building blocks for molecular magnetic materials. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 289
    Electronic Resource
    Electronic Resource
    Kinetic study of base-promoted elimination reactions of some 1,1,1-trihalo-2,2-bis(dimethoxyphenyl)ethanes in alcoholic solutions (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 54-58 
    Details
    ISSN: 0894-3230
    Keywords: 1,1,1-trihalo-2,2-bis(dimethoxyphenyl)ethanes ; base-promoted elimination ; reaction mechanism ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The base-promoted elimination reactions of 1,1,1-trichloro-2,2-bis(dimethoxyphenyl)ethanes were investigated. The bis(3,4-dimethoxyphenyl)ethane was found to be more reactive than the bis(2,5-dimethoxyphenyl)ethane and the latter more reactive than the bis(2,4-dimethoxyphenyl)ethane. Kinetic data relative to 1,1,1-trihalo(chloro or bromo)-2,2-bis(3,4-dimethoxyphenyl)ethanes show that the tribromo reacts faster than trichloro derivative and that the reactions are general-base promoted with Brønsted β values of about 0.6. A kinetic isotope effect, with kH/kD ratio ranging from 3.5 to 5.7, for the base-promoted elimination reaction of 1,1,1-trichloro-2,2-bis(3,4-dimethoxyphenyl)ethane was found. Tunneling occurs for methoxide and ethoxide ion-promoted eliminations. Activation parameters for alkoxy-promoted elimination show a similar trend for chloride and bromide derivatives. The data collected seem to confirm that there is contiguity between E1cBirr and E2 mechanisms. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 290
    Electronic Resource
    Electronic Resource
    Kinetic and thermodynamic study of 2-bromo-2-methylbutane, 2-chloro-2-methylbutane and 3-chloro-3-methylpentane in diols (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 36-40 
    Details
    ISSN: 0894-3230
    Keywords: haloalkanes ; diols ; kinetics ; thermodynamics ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rate constants, k, were determined for the solvolytic reactions of 2-bromo-2-methylbutane, 2-chloro-2-methylbutane and 3-chloro-3-methylpentane in 10 pure diols at 298.15 K. The Gibbs energies of activation were calculated in order to study the influence of the solvent and to provide mechanistic information about the activation process. By combining these values with a set of infinite dilution activity coefficients, γ∞, the transfer Gibbs energies of the reactants (initial state) and of the activated complex (transition state) were obtained, which allowed the solvent effects on both states to be quantitatively analysed. The γ∞ values were calculated using the UNIFAC group contribution method. The modified Flory-Huggins equation was used in the combinatorial term. The interaction parameters were taken from the specific UNIFAC γ∞ interaction parameter table, except for the γ∞ values of 2-chloro-2-methylbutane and 3-chloro-3-methylpentane in diethylene glycol and triethylene glycol, which were obtained using the γ∞ UNIFAC-VLE interaction parameter tables. For comparative purposes all the other infinite dilution activity coefficients of the three solutes in the diols were also calculated using the UNIFAC-VLE parameter tables. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 291
    Electronic Resource
    Electronic Resource
    Inhibitory effect of DNA structure on the efficiency of reaction of guanosine moieties with a nitrenium ion (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 71-76 
    Details
    ISSN: 0894-3230
    Keywords: guanosine ; nitrenium ; DNA structure ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The N-acetyl-N-(2-fluorenyl)nitrenium ion (2a) reacts very efficiently with monomeric 2′-deoxyguanosine (d-G) to form a C-8 adduct, N-(2′-deoxyguanosin-8-yl)-2-acetylaminofluorene (6), in an aqueous environment, with a selectivity ratio, kd-G/ks, of 13.1 × 103 M-1 at 0°C and 4.8 × 103 M-1 at 30°C. The reactivity of the self-complementary oligomer d-ATGCAT with 2a can be separated into components due to the single-stranded (SS) and double-stranded (DS) forms. Within the error limits of the measurements kSS/kd-G ≈ 0.27 and kDS/kd-G ≈ 0. Another measure of the reactivity of d-G moieties in the DNA double helix can be obtained from measurements with the circular super-coiled plasmid pUC19. This plasmid provides an upper limit for kpUC19/kd-G of 0.02, where kpUC19 is the average trapping rate constant per d-G moiety in pUC19. The strong inhibition of the trapping reaction caused by the tertiary structure of the DNA double helix may be responsible for the change in product distribution of 2a-d-G adducts found from reaction with d-G, and denatured DNA (exclusive C-8 adduct, 6) and native DNA [5-20% N-2 adduct,3-(2′-deoxyguanosin-N2-yl)-2-acetylaminofluorene, 7]. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 292
    Electronic Resource
    Electronic Resource
    Effects of urea, Na+ and Li+ ions on the kinetics and mechanism of intramolecular general base-catalyzed glycolysm of ionized phenyl salicylate in ethane-1,2-diol-acetonitrile solvents at a constant water concentration (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 109-114 
    Details
    ISSN: 0894-3230
    Keywords: phenyl salicylate ; ethane-1,2-diol ; urea ; sodium salt ; lithium salt ; transesterification ; kinetics ; intramolecular general base catalysis ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Pseudo-first-order rate constants (k1) for the reaction of ethane-1,2-diol (DOL) with ionized phenyl salicylate (PS-), obtained in mixed DOL-CH3CN solvent at constant [H2O] and [NaOH], obey the relationship k1  =  α[DOL]T/(1 + 2KA[DOL]T), where α is the apparent second-order rate constant, KA is the association constant for the dimerization of DOL and [DOL]T is the total concentration of DOL. The values of KA, in the presence of Na+ ions, decrease with increase in [H2O]. Lithium ions cause almost complete depolymerization of polymeric DOL (i.e. KA ≈ 0) under the experimental conditions imposed. The effect of 0.5 M urea on the structural behavior of the mixed solvent is kinetically insignificant. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 293
    Electronic Resource
    Electronic Resource
    Solvolysis of isodrin derivatives. Evidence of long-range σ-participation in the stabilization of carbocations (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 871-878 
    Details
    ISSN: 0894-3230
    Keywords: laticyclic hyperconjugation ; isodrin ; solvolysis ; through-bond and through-space interactions ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Enhanced rates of solvolysis have been reported for some isodrin derivatives, e.g. compounds 2, 3, 6 and 7 compared with anti-7-norbornene (1). The effect has been ascribed to the formation of laticyclic (2 + 2 + 0) π-delocalization on a carbocation such as 5. However, comparable rates of solvolysis were also observed for analogous monoenes 4, 8, 9 and 12, where no adequate explanation has been provided. Molecular modeling at both semiempirical and ab initio levels shows a good correlation between the stabilization energy of the cations and their kinetic data. The enhanced rate of solvolysis for 4, 8, 9 and 12 can be rationalized by strong effects of σ-bond participation in the transition state. For both series of compounds, the stabilization effect can be effectively transmitted either through space or through bonds. Copyright © 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 294
    Electronic Resource
    Electronic Resource
    Intramolecular thermal (4σ + 2π) dyotropy: primary 2H kinetic isotope effects. Experimental limiting barrierparameters for quantum tunnelling in 2H transfer processes and mechanistically significant substituent effects (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 879-886 
    Details
    ISSN: 0894-3230
    Keywords: intramolecular thermal (4σ + 2π) dyotropy ; kinetic isotope effects ; limiting barrier parameters ; quantum tunnelling ; 2H transfer processes ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Primary deuterium kinetic isotope effects (PDKIE) in parazoline-annelated syn-sesquinorbornenes exhibiting irreversible intramolecular (4σ + 2π) thermal dyotropy reveal unambiguous evidence for a tunnelling contribution to the kinetics in one instance but not for a close analogue. For analogous dyotropy of a cyclohexadiene-annelated syn-sesquinorbornene, the tunnelling components of the kinetic behaviour is small by comparison. The H atom traverse between alternative loci for the pyrazolines, deduced from x-ray and neutron diffraction data, is in agreement with approximate barrier parameters obtained by fitting of the PDKIE data to the Bell equation; barrier penetration is 3.22 kcal below the computed barrier corrected for the tunnelling contribution. The relative kinetic effect of systematic variation of the π-donor/acceptor groups on aryl ring substituents at C and N in the pyrazoline ring is consistent with a pericyclic process for dyotropy of these compounds, but not with rearrangement mediated by biradicals resulting from single H atom transfer in the rate-limiting step. Computer modelling of the transition state for dyotropy of these compounds is also consistent with a thermal, orbital symmetry conserved pericyclic reaction. Copyright © 1998 John Wiley & Sons, Ltd.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 295
    Electronic Resource
    Electronic Resource
    Reactant-solute encounters in aqueous solutions studied by kinetic methods: hydration cosphere overlap and camouflage effects (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 841-846 
    Details
    ISSN: 0894-3230
    Keywords: reactant-solute encounters ; aqueous solutions ; water ; kinetic methods ; hydration cosphere destructive overlap ; camouflage effects ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rates of chemical reactions in aqueous solutions are often sensitive to low concentrations of added solutes such as ureas, alcohols, α-amino acids and carbohydrates. In this work, several simple chemical reactions were used to probe this sensitivity, which arises from interactions between added solute and the reacting solute. It was found that derived interaction parameters provide a novel insight into interactions between solute molecules in aqueous solution. For example, it was possible to identify two interesting effects, which are termed (i) ‘destructive overlap’ of hydration cospheres and (ii) ‘camouflage effects’ by water-solute interactions. Copyright © 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 296
    Electronic Resource
    Electronic Resource
    Conjugate addition of water to α-carbonylcarbenes (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 610-613 
    Details
    ISSN: 0894-3230
    Keywords: Conjugate addition ; α-carbonylcarbenes ; water ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: α-Carbonylcarbenes (2a-c) generated by UV photolysis of 2-diazophenylacetic acid (1a), its methyl ester (1b) and 4-diazo-3-isochromanone (1c) in aqueous solution undergo conjugate addition of water across the entire carbonylcarbene moiety to give enols (3a-c) of the corresponding α-hydroxycarbonyl compounds. These carbenes are long-lived, with microsecond lifetimes in aqueous solution. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 297
    Electronic Resource
    Electronic Resource
    Rhodium(II)-catalyzed nitrene transfer with phenyliodonium ylides (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 597-601 
    Details
    ISSN: 0894-3230
    Keywords: rhodium(II)-catalyzed nitrene transfer ; phenyliodonium ylides ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The [Rh2(OAc)4]-catalyzed decomposition of NsN=IPh {[N-(p-nitrobenzenesulfonyl)imino]phenyliodinane} affords aziridines in the presence of olefins and insertion products with compounds having activated CH bonds. The aziridination is stereospecific, and the insertion proceeds with retention of configuration. With chiral Rh(II) complexes, enantioenriched products result. A one-step mechanism involving a metal-complexed nitrene is proposed for both reactions. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 298
    Electronic Resource
    Electronic Resource
    Predicting the rates of proton transfer reactions: a simple model using equilibrium constants and distortion energies (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 632-641 
    Details
    ISSN: 0894-3230
    Keywords: proton transfer reactions ; rate prediction ; equilibrium constants ; distortion energies ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A simple model for the energy surface of a reacting system permits the calculation of the free energies of activation. A chemical reaction is analyzed in terms of the simple processes (bond making/breaking or atom transfer; geometry changes) which must take place to achieve the overall transformation. When only one (or two, or three, …) of these processes has progressed to the full extent required for reaction, one has a ‘corner intermediate.’ The reaction diagram is viewed as a square (2D) or cube (3D) or hypercube (4D), etc., and energies at intermediate points on the energy surface or hypersurface are calculated by interpolation. Suitable equations have been obtained for this purpose. Along any section parallel to an axis the energy is given by an upward opening parabola centered at the lower energy end. This paper deals with the application of these ideas to proton transfer reactions involving carbon acids. For mono- or dicarbonyl compounds, with pKas ranging from 7 to 25.6, and rate constants for water or hydroxide ranging from 10-9.3 to 104.6, rate constants can be predicted with an r.m.s. error in log k of 0.99 for 51 reactions. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 299
    Electronic Resource
    Electronic Resource
    From olefin cyclopropanation to olefin metathesis through catalyst engineering: recent applications of olefin metathesis to fine organic synthesis and to polymer chemistry (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 602-609 
    Details
    ISSN: 0894-3230
    Keywords: olefin metathesis ; olefin cyclopropanation ; catalyst engineering ; fine organic synthesis ; polymer chemistry ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An overview of the recent synthetic breakthroughs brought about by the discovery of new, functional group tolerant late transition metal (Rh and Ru)-based catalysts is proposed. Whereas dirhodium(II)-based complexes promote only carbene transfer reactions to olefins (i.e. olefin cyclopropanation), a few ruthenium-based catalysts can be engineered and fine tuned so as to mediate either carbene-transfer reactions or olefin metathesis. The different outcome of the reactions can be rationalized by the capability of the metal center to coordinate or not both the carbene and the olefin. This quite simple-minded approach indicates that several available coordination sites at the metal center favors metathesis reactions to the prejudice of olefin cyclopropanation. Examples of recent applications in ring opening metathesis polymerizations and copolymerizations include the formation of postpolymers of polydienes, of carbohydrate-substituted polymers and of telechelic oligomers. Application of the same ruthenium-based catalysts in ring-closing metathesis is illustrated by the formation of crown ether analogs, of unsaturated peptides and amino acids, of β-lactams, and of different bicyclic systems.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 300
    Electronic Resource
    Electronic Resource
    Imperatives for enzymatic catalysis of isomerization of sugars and sugar phosphates (1998)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 512-518 
    Details
    ISSN: 0894-3230
    Keywords: sugar isomerization ; sugar phosphate isomerization ; enzymatic catalysis ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relative yields of the products of isomerization of D,L-glyceraldehyde in D2O with intramolecular transfer of a hydride ([1-1H]DHA) and with proton transfer ([1-2H]DHA) were determined by high-resolution 1H NMR analyses. A study of the catalysis of this isomerization by deuteroxide ion, buffer anions and Zn2+ established the following: (1) isomerization with proton and hydride transfer occurs at approximately equal rates in dilute solutions of sodium deuteroxide; (2) Brønsted bases catalyze isomerization with proton transfer in a bimolecular reaction; (3) Zn2+ catalyzes isomerization with hydride transfer in a bimolecular reaction; and (4) Zn2+ and acetate ion react in concert to catalyze isomerization with proton transfer in a termolecular reaction. These results show that the various pathways for isomerization with proton and hydride transfer proceed via transition states of similar energies, so that there is no strong imperative for enzymatic catalysis by any particular reaction mechanism. The relevance of these results to the mechanism of action of xylose isomerase is discussed briefly. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...