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  • 1990-1994  (1,534)
  • 1925-1929
  • 1991  (1,534)
  • General Chemistry  (1,091)
  • Atomic, Molecular and Optical Physics  (238)
  • Physical Chemistry  (205)
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Material
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  • 1990-1994  (1,534)
  • 1925-1929
Year
Keywords
  • 101
    Electronic Resource
    Electronic Resource
    Analysis of the density-gradient-expansion approximation for the exchange-correlation energy of density-functional theory (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 235-248 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To understand the density-gradient expansion approximation for the exchange-correlation energy of density-functional theory from a fundamental viewpoint, we have performed an analysis of the corresponding expansion of the Fermi-coulomb hole charge distribution. The Fermi-Coulomb hole represents the correlations between electrons resulting from the Pauli exclusion principle and Coulomb's law. The analysis is performed in the exchange-only approximation by considering the expansion for the Fermi hole to terms of O(▽3) as applied to atoms. Our study shows that the expansions to O(▽), O(▽2), and O(▽3) all severely violate the constraint of positivity, becoming progressively worse with increasing orders of ▽. Further, the expansion to O(▽2) also severely violates the constraint of charge neutrality. (Terms of O(▽) and O(▽3) do not contribute to this constraint or to the exchange energy.) Thus the description of the physics of Pauli correlations in atoms as given by this approximation is highly unphysical. In spite of this, the exchange energy to O(▽2) is superior to the local density approximation because the expansion hole better approximates the exact Fermi hole in the interior of atoms from which arise the principal contributions to the energy. However, the improvement is not substantial, as the oscillations in the expansion Fermi hole occur within the atom itself. For asymptotic positions of the electron, the expansion holes to each order neither approximate the local density approximation nor the exact Fermi hole. Thus we understand why the expansion cannot lead to accurate highest occupied eigenvalues. The oscillations of the expansion Fermi hole also demonstrate why the Slater potential and electric field that result from these hole charge distributions are singular. On the other hand, we show that the expansion approximation is mathematically consistent in that the coefficient of the gradient correction term for screened Coulomb interaction to O(▽2) as obtained from the approximate Fermi hole is the same as that derived from linear response theory. We conclude with remarks on the Coulomb hole as obtained within this gradient expansion approximation scheme.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400824
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  • 102
    Electronic Resource
    Electronic Resource
    Calculation of the total atomic binding energy with recently proposed kinetic-, exchange-, and correlation-energy functionals (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 261-268 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The functionals adopted in the present work are those of DePristo and Kress [Phys. Rev. A35, 438 (1987)] for the kinetic energy, of Cedillo et al. [Phys. Rev. A38, 1697 (1988)] for the exchange energy, and of Wilson and Levy [Phys. Rev. B41, 12930 (1990)] for the correlation energy. In addition to the kinetic-, exchange-, and correlation-energy functionals, the total-energy functional used in the present calculations contains also the functional describing the interaction of the electrons with the atomic nucleus, and the functional describing the classical or direct part of the interaction among the electrons. Using these functionals, a two-parameter and a three-parameter variational density-functional calculation of the total atomic binding energy of the Ne atom is carried out. The electron (number) density of the Ne atom is modeled by using hydrogenlike one-electron radial wavefunctions (with the 2s radial function orthogonalized to the 1s radial function) containing two/three variational parameters. It is found that the calculated correlation energies are in reasonable agreement with the correlation energy value obtained from the Wilson and Levy expression with a Hartree-Fock electron density.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400826
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  • 103
    Electronic Resource
    Electronic Resource
    Application of local-density functional theory to molecules containing a hypervalent bond (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 269-279 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular and electronic structures of ADPO 1, a model thiapentalene 2, and [Xe2F3]+ have been calculated in the local-density functional (LDF) formalism with polarized double numerical basis sets. The molecules were calculated to have planar C2ν structures in agreement with experiment and in contrast to Hartree-Fock molecular-orbital calculations. The vibrational spectra of all species were calculated to show that the optimized structures are indeed minima. The calculated spectrum of [Xe2F3]+ is compared with the experimental one and excellent agreement is found. These results demonstrate that the LDF method can be applied to the prediction of molecular structures containing hypervalent bonds.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400827
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  • 104
    Electronic Resource
    Electronic Resource
    Nonadiabatic molecular dynamics (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 299-309 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular dynamics simulation of mixed quantum-classical systems, in situations where the quantal degrees of freedom undergo transitions among states, poses a number of challenging problems. Among the difficulties are bifurcation of trajectories that evolve into different quantum states and proper treatment of quantum coherence. In this article we outline the problems and contrast the ways in which they are addressed by current methods for nonadiabatic molecular dynamics. In the course of this comparison we present a new result, the relationship between the velocity adjustment in the “surface hopping” method and the “Pechukas force,” as well as some new reflections on an old result, oscillatory yields in ion-surface scattering.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400830
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  • 105
    Electronic Resource
    Electronic Resource
    Density-functional theory of the superconducting state (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 289-297 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A density-functional theory describing the superconducting state of matter is presented. The formalism leads to a set of single-particle equations that are structurally similar to the Bogoliubov-de Gennes equations but (in contrast to the latter) incorporate both normal and superconducting exchange-correlation effects. It is demonstrated via a rigorous decoupling scheme that these single-particle equations are equivalent to a set of normal Kohn-Sham equations, and a BCS-type gap equation to be solved self-consistently with the Kohn-Sham equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400829
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  • 106
    Electronic Resource
    Electronic Resource
    Path integral approach to chemical dynamics: A test case of H + O2 ↔ OH + O reaction (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 311-323 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Determining mechanisms of chemical reactions involves finding dynamical paths between desired (given) reactant and product states. We have developed a method that is based on recasting the principle of stationary action into a general and computationally tractable form that yields all dynamical paths connecting the initial and final configurations of the system. Thus the method has advantages over the traditional initial-value trajectory calculations for solving such boundary value problems. We give some examples of reaction paths for H(2S) + O2(3Σg-) ↔ OH(2II) + O(3P) on the ground state potential energy surfaces HO2(2A″).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400831
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  • 107
    Electronic Resource
    Electronic Resource
    Ion solvation energies from density functional theory (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 281-288 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrostatic solvation energies of singly charged monoatomic ions may be predicted from the knowledge of an electrostatic potential buildup from a physically meaningful ionic radius. Since the asymptotic behavior of the electrostatic potential for cations and anions do not follow the same pattern, different methodologies are needed. The reaction field potential required for the calculation of Born's solvation energies of singly charged cations may be obtained from the simple Thomas-Fermi-Dirac theory, based on the condition that the electrostatic potential of the ground-state atomic ions do exactly equal the negative of their chemical potentials. For singly charged anions, electrostatic solvation energies may be directly obtained from Sen-Politzer electrostatic potentials. Numerical results are presented for two representative series of ions and compared with experimental data.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400828
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  • 108
    Electronic Resource
    Electronic Resource
    Electrophilic substitution in the benzofuran series: A theoretical (AM1) study (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 325-333 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrophilic substitution in a series of 5-aminobenzofurans was investigated by all-valence electron AM1 molecular orbital calculations. Various molecular properties of the reactants, intermediates, and products were computed and compared with available experimental data. The results indicate that while calculated ground-state charge densities cannot be used to predict reactivity and orientations, the relative thermodynamic stabilities of the reaction intermediates (arenium ions, σ complexes) reflected by calculated heats of formation (ΔHƒ) accurately indicated the isomers resulting from the kinetically controlled substitutions. The relative stabilities of the reaction products could be used to predict reaction preferences for the thermodynamically controlled electrophilic substitutions. Positions 4 for both aniline and 5-aminobenzofurans were the most susceptible toward electrophilic attack. The calculated ΔHƒ of the reaction intermediates, in good agreement with the experimental data, were capable of distinguishing between slightly nonequivalent positions such as the ortho and ortho prime to a substituent. Calculated AM1 ΔHƒ may represent practical guides in the prediction of sites of electrophilic aromatic substitutions for molecules with complex structures.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400832
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  • 109
    Electronic Resource
    Electronic Resource
    Intermolecular dynamics for weakly bound donor-acceptor complexes (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 347-358 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have performed ab initio (3-21 G) calculations on the weakly bound donor-acceptor complex between benzene and tetracyanoethylene (TCNE) as a function of various intermolecular motions. The resultant potential energy surface (PES) was then fit to the product of analytical functions. Classical dynamics was performed on this PES by solving Hamilton's equations using a fourth-order Runge Kutta differential equation solver. Time steps were of the order of 1.0 femtosecond and the system was allowed to evolve for 1,000,000 time steps. Fast Fourier analysis of the resulting trajectories indicate that the primary intermolecular vibrational frequencies are 118, 228, and 232 cm-1. These correspond to the motion of the intermolecular separation coordinate, and the two twisting coordinates. We also discuss other possible solutions, zero-point energies, etc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400834
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  • 110
    Electronic Resource
    Electronic Resource
    On molecules and ions in strong magnetic fields (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 371-385 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Some of the fundamental theoretical concepts for molecules in homogeneous strong magnetic fields are discussed. First, we perform the pseudoseparation of the center of mass motion for neutral as well as charged systems. The resulting Hamiltonian allows us to investigate the problem of the Born-Oppenheimer adiabatic separation of electronic and nuclear motion in the presence of a magnetic field. In particular, we study the most important differences to the field-free case. Finally we discuss the symmetry groups for molecules in a magnetic field and investigate the possibilities and effects of the interaction of molecular electronic states through nuclear motion. Even for diatomic molecules severely enhanced nonadiabatic effects may occur in a magnetic field.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400836
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  • 111
    Electronic Resource
    Electronic Resource
    Shape analysis along reaction paths of ring opening reactions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 335-345 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work we analyze the interrelations between potential energy changes and molecular shape changes along the reaction paths for a series of ring-opening reactions. The processes studied correspond to the opening of the four-member rings of 1,2-dioxete, 2H-oxete, 2H-thiete, and 1,2-dithiete, which recently have been given considerable attention in the literature. We describe the molecular shape in terms of a continuum of fused-sphere surfaces, which are characterized by using molecular topological methods. The four processes cover a range of reaction enthalpies from largely exothermic to almost thermoneutral. The similarity between the configurations found along the reaction path is assessed quantitatively in terms of parameters associated with the molecular shape and the path itself. We find a correlation between the value of the energy barriers (and reaction enthalpies) and the similarity parameters. The correlation is comparable to that found in the case of various other processes, such as torsional changes, collisions, and intramolecular atom displacements or shifts. The results are in line with the intuitive correlations expected from the Hammond postulate.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400833
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  • 112
    Electronic Resource
    Electronic Resource
    Kinematic distribution function to calculate rotational populations of photofragments from photodissociation of triatomic molecules (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 359-370 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general procedure to evaluate the rotational state population distributions of the nascent photofragments from the photodissociation of polyatomic molecules has been implemented with the use of the kinematic distribution function developed by Chen and Pei [Chem. Phys. Lett. 124, 365 (1986)]. Numerical evaluations of rotational state population distributions of diatomic photofragments from photodissociation of the general class of triatomic molecules are presented. The calculated rotational state population distributions are compared with the most recent experimental data on OH and SH photofragments to obtain the information on the kinematic aspects of the photodissociating H2O and H2S molecules.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400835
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  • 113
    Electronic Resource
    Electronic Resource
    Atoms and ions in intense magnetic and electric fields (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 401-414 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The study of atoms and ions in unusual environments is an area of current interest. Examples of such environments are the Crab pulsar, where magnetic fields well in excess of 1012 G are encountered and plasmas, studied under intense laser irradiation, where “confined” atoms are subjected to electric fields corresponding to laser fluxes of 1018 W/m2. In this article, a unified theoretical approach is presented to treat atoms in such intense fields. The major theoretical tool employed is the Bloch or canonical density matrix. This is used first for treating magnetic fields, numerical examples of heavy atoms, and ions in intense fields being referred to specifically. Then the same theory is used for “confined” atoms in intense electric fields. Very brief reference is made to molecules in magnetic fiels, with the illustrative example of the simplest molecular ion H2+.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400838
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  • 114
    Electronic Resource
    Electronic Resource
    Single-active electron calculation of multiphoton process in krypton (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 415-429 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We employ a method for solving the time-dependent Schrödinger equation for an atom or molecule in an intense, pulsed-laser field to study multiphoton emission processes. Single-electron effective potentials have been developed that reduce the computational effort required for multielectron systems. Illustrative results for electron and photon emission rates from krypton at 532 nm in the intensity range (1-4) × 1013 W/cm2 are presented and compared to recent measurements.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400839
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  • 115
    Electronic Resource
    Electronic Resource
    Time-Resolved magnetic field effects in the recombination products of geminate triplet pairs for electron phototransfer reactions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 387-399 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We studied the influence of the additives of tetracyanoethylene (TCE) (radical-anion acceptor) and the variations in exciplex concentration on the magnitude of time-resolved magnetic field effect in a delayed excimer fluorescence in polar exciplex system pyrene-N,N-diethylaniline. The nonmonotonous dependence of the magnetic field effect on tetracyanoethylene concentratration was found. The magnitude of the magnetic field effect was brought close to the predicted maximum limit of about 300 ns by decreasing the exciplex concentration. We conclude that the yield of the triplets, resulting from intercombination transitions in a singlet exciplex, is rather small. The upper limit for the rate constant of these transitions has been determined to be less than 4.6 × 106 s-1.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400837
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  • 116
    Electronic Resource
    Electronic Resource
    Hund's second rule and the electronic structure of transition-metal oxides (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 431-440 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An orbital polarization (Hund's second rule) correction to local spin density (LSD) theory is developed in both a spherical harmonic basis and in a crystal field basis, and applied to the electronic band structure of FeO, CoO, NiO, and La2CuO4, resulting in a substantial enhancement of the LSD insulating band gap for NiO, and the creation of insulating band gaps for FeO, CoO, and La2CuO4.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400840
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  • 117
    Electronic Resource
    Electronic Resource
    Variational calculations on ammonia using two symmetrical normal modes (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 441-450 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Variational calculations have been carried out on the ammonia molecule using two-dimensional potential energy functions. The two dimensions used are the inversion and symmetrical stretching coordinates. If the potential function includes a term to describe the interaction between these two coordinates, the results are as good as those obtained in other studies using a six-dimensional potential function. The barrier height for the new potential function is 1857.5 cm-1.
    Additional Material: 10 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400841
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  • 118
    Electronic Resource
    Electronic Resource
    Theoretical and experimental study on small molecular ions. I. Ab Initio calculations on CSe, CSe+, and HCSe+ species (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 451-459 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio molecular-orbital calculations were carried out on carbon monoselenide (CSe), its cation CSe+, and the selenoformyl cation HCSe+. Equilibrium- and transition-state geometries on the potential energy surfaces (PES) were located at the HF and MP2 levels using a valence double-ζ (d, p) basis set on H and C and the Huzinaga valence triple-ζ (d) basis set on selenium, respectively. The global minimum on the HCSe+ (PES) is the linear species 3 with the dissociation energy towards H and CSe+ of 151.5 kcal mol-1 (MP4//MP2 + ZPE level). While at the HF level the strongly bent isomer 4 is a local minimum structure lying 67.8 kcal mol-1 above 3 and separated from 3 by a small barrier of 6.2 kcal mol-1, MP2 geometry optimizations suggest that CSeH+ isomer is unstable.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400842
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  • 119
    Electronic Resource
    Electronic Resource
    Photoelectron spectra of halogenofurans (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 479-487 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The UV photoelectron spectra of 2-halogenofurans, together with 3-iodo and 2,5-diiodofurans, have been studied. The assignment of the lower energy region of the spectra was based on correlation of the ring π- and halogen levels in the related compounds, resolved vibrational structure, and in case of 2- and 2,5-diiodofurans by considering the relative intensities of their He I/He II spectra.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400844
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  • 120
    Electronic Resource
    Electronic Resource
    Comparative Ab Initio study of electronic and ionic properties of lithium nitride (Li3N), lithium phosphide (Li3P), and lithium arsenide (Li3As) (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 461-478 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio Hartree-Fock band structure calculations are presented for the first time for lithium phosphide (Li3P) and lithium arsenide (Li3As) in the hexagonal P6/mmm crystal structure. Results are compared to those for lithium nitride (Li3N). The new calculations for Li3N agree with previous Hartree-Fock calculations, except for the valence band structure where results of previous pseudopotential calculations are confirmed. Geometry optimization for Li3P yields a lattice parameter a of 4.45 Å and a c value of 4.80 Å. These values differ markedly from experimental results reported to be 4.271 and 7.590 Å, respectively. A similar discrepancy is found for lithium arsenide: a = 4.60 Å and c = 4.96 Å have to be compared to the reported experimental values of 4.397 Å for a and 7.824 Å for c. Force constants are derived for in-plane and interplane vibrations. The band structures for Li3P and Li3As are found to be very similar to the one calculated for Li3N. Using Li3P as an example, it is shown how the band structure of the insulator can be derived from the band structures of the two metallic constitutent Li2P and Li monolayers. The metal-insulator transition occurs if the inter-plane distance falls below 4.25 Å. Contrary to expectations raised earlier, it is found that the 3d electrons in arsenic are strongly localized, evidenced by a very narrow d band width of 0.1 eV. They cannot be used to explain the difference in conductivity between the phosphide and the arsenide. A Mulliken population analysis gives charge distributions close to the ideal ionic structure (Li+)3X3-, X = N, P, and As. Overall it is found that hexagonal lithium phosphide and lithium arsenide arsenide are more similar to lithium nitride and less anisotropic than suggested previously. This discrepancy could be due to the use of polycrystalline samples in earlier experiments.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400843
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  • 121
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    1,5-C2B3H5 and C5H8, 1,5-C2B3H3 and C5H6: Carborane-hydrocarbon structural analogs with unusual three-center bondsDedicated to William Nunn Lipscomb in honor of his many important contributions to structural and theoretical chemistry. (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 489-505 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electronic structure of the polyhedral carboranes 1,5-dicarba-closo-pentaborane(5) and 1,5-dicarba-closo-pentaborane(3) is studied using ab initio calculations, and compared to that of their hydrocarbon analogs bicyclo[1.1.1]pentane and [1.1.1]propellane, respectively. The high symmetry and common topology of the carborane-hydrocarbon structural analogs force similar bonding patterns, and the carboranes show a unique three-center, two-electron CBC bond not previously observed in these species. This three-center bond is formally analogous to the σ-bridged-π bond in the hydrocarbons, but its strength is low and its C—C bond long. Analysis of the bonding in these carboranes along with that in 1,3-diborabicyclo[1.1.1]pentane, another[1.1.1]propellane analog, shows that the strength of their three-center bonds is directly related to the nature of the bridging group, but is independent of the type of bridgehead atom. 1,3-Diboretene, the carborane analog of bicyclo[1.1.0]butane, is also found to exhibit a similar bonding pattern to its hydrocarbon analog and to possess a CBC bond.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400845
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    Preliminary theoretical study of acrylonitrile and its methyl derivatives as monomers for cathodic electropolymerization (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 507-526 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio calculations of the molecular geometry and electronic structure properties (charges, dipole moment, polarizability, HOMO and LUMO energies) of acrylonitrile, CH2=CH—C≡N, cis- and trans-2-butenenitrile, CH3—CH=CH—C≡N, 3-butenenitrile, CH2=CH—CH2—C≡N, and 2-methyl-2-propenenitrile, CH2=C(CH3)—C≡N are obtained at the 3-21G level. Results on three anionic derivatives of these molecules obtained at the 3-21+G level are also reported. Properties of the molecules in their isolated states are considered as a preliminary basis to compare initial steps of bulk and surface polymerization of vinylic monomers by electrochemistry under cathodic polarization.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400846
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    Solvation effects on the structure and reactivity of clusters (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 527-544 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Elucidating, from a molecular point of view, the differences and similarities in the properties and reactivity of matter in the gaseous compared to the condensed state is a subject of considerable current interest. Although there are a number of promising approaches to this problem, one of the alternatives involves the use of clusters that enable detailed spectroscopy and reactivity investigations to be accomplished as a function of degree of solvation under well controlled conditions. New insight into a variety of phenomena of interest in liquids have been derived from recent studies in our laboratory. In particular, the findings have contributed to unraveling the reactions of ionized functional groups in organic molecules that are influenced by solvation effects, identifying the structure of protonated complexes among species of varying proton affinities, and quantifying the variations in spectroscopic properties of chromophores as influenced by solvation and aggregation. Various examples from the author's laboratory are discussed, including solvation-driven reactions as well as alcohol and acetone dehydration reactions, the influence of clustering on the reaction of OH- with CO2, structures of protonated species comprised of water, ammonia, and trimethylamine; also presented are the results of studies of the influence of solvation on the absorption of photons in the chromophore of tyrosine, namely phenol.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400847
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    Calculations on the electronic structure and spectroscopy of C60 and C70 cage structures (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 557-568 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study of the electronic structure and spectroscopy of models of C60 and C70 cage structures has been carried out using the intermediate neglect of differential overlap (INDO) model Hamiltonian. The geometry for these cages was obtained using gradient-driven methods, and at least in the case of C60, where information is available, is in good accord with the calculations of others. Using a small active space of only single excitations, both configuration interaction (CI) and random phase approximations (RPA) yield spectra in excellent agreement with that obtained from recent experiments. The oscillator strength of the band calculated at ∼47000 cm-1, however, dramatically diminishes as the active space is increased, even though the sum rule increases. We discuss this interesting observation as well as the calculated structure and spectrum of C70.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400849
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    An INDO/S-CI treatment including spin-orbit interaction based on Rumer spin functions. Application to the hydrated cerium ion (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 545-555 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We examine the inclusion of spin-orbit effects within the Rumer configuration interaction technique and discuss its implementation in the spectroscopic version of the intermediate neglect of differential overlap model (INDO/S-CI). An efficient strategy for calculating excitation energies, transition moments, and Mulliken populations for Rumer-adapted functions is described. As an example, results are presented for the ground and excited states of the hydrated trivalent cerium ion [Ce(H2O)9]3+, which confirm the low energy assignments to 4ƒ → 5 d transitions split by some 10000 cm-1 through spin-orbit coupling and ligand field interaction. Comparisons are made between this technique and one that we have used previously that utilizes configuration interaction over double-group adapted linear combinations of determinants.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400848
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  • 126
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    Electron-Atom interaction potential by DCS minimization (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 569-576 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The angular and energy dependence of minima of the differential scattering cross section (DCS) for electrons scattered elastically by selected target atoms is studied using the nonrelativistic Hartree-Fock wavefunction for the static field and local energy-dependent function for the exchange and polarization potentials for the target atoms. The parameters contained in the polarization potential are varied to determine the minima of the DCS with respect to the scattering angle and incident energy with the constraint that the integral cross section agrees with the experimental value within the uncertainty of 5% at a selected energy. The resulting effective interaction potential is then used to compute the DCS over the intermediate energy range for the target atoms. The computed values are in good agreement with recently published experimental and theoretical cross section for helium and neon atoms.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400850
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    A theoretical study of the photochemistry of methylcopper hydride: II. Formation and stability of the HCuCH3 intermediate complex (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 577-585 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using computational SCF and MCSCF followed by extensive variational and perturbational CI calculations, we study the insertion routes of a copper atom into the carbon-hydrogen bond of a methane molecule. Here we show the importance of the initial reaction routes of the interaction for obtaining the final products of maximal probability. Because of the initial conditions of this reaction, our study shows that not all of the HCuCH3 intermediate complex dissociation channels in Part I can be easily reached. Another important result presented is the nonlinearity of the intermediate product HCuCH3. Finally, the results are discussed in light of low temperature matrix photoexcitation experiments and a comparison of this Cu—CH4 interaction with previous studies of the activation of the hydrogen molecule by copper is presented.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400851
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    The charge distribution and the electric field gradient at the nuclei of two-coordinated N atoms (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 587-591 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From ab initio SCF-MO calculation using a 6 - 31G** basis set, the relationship between the topology of the charge distribution and the electric field gradient (EFG) at the nuclei of the two-coordinated N atoms was determined in imines with R = H2C =, HFC =, NCHC =, and H3CHC =; di-imides with R = H, F, and CN; and the monocyclic azines with one and two N atoms in it. It was found that the N nuclear quadrupole coupling constant was determined by the nonbonded concentration of N valence shell while the asymmetry parameter has contributions from this shell and also from the rest of the molecule.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400852
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    Intermolecular vibrational resonance coupling: Intensity borrowing in polarized Raman spectroscopy (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 593-602 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of solvent-solute interactions on polarized and depolarized Raman intensity are investigated using perturbation theory, accounting for correlations in the relative orientations of the interacting transition dipoles. Two mechanisms for intensity borrowing are considered: interaction of the vibrational transition moments in the ground electronic states, and coupling of the electronic transition moments responsible for resonance Raman enhancement. The first type of interaction is shown to lead to measurable frequency shifts and depolarization ratio changes for two coupled vibrations which are infrared active and close in frequency. The second mechanism, not dependent on vibrational resonance, leads to perturbations of the depolarization ratio in resonance Raman, but not to vibrational frequency shifts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400853
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    An Ab Initio computational scheme for polymeric chains with fully converged coulomb and exchange lattice sums (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 603-618 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The restricted Hartree-Fock formalism applied to quasi one-dimensional translational systems embodies slowly convergent Coulomb and exchange lattice summations. In this contribution, an algorithm based on a Filon like quadrature procedure to carry out the k-space integration of density matrix elements is analyzed and its efficiency is illustrated by its application to the linear chains of hydrogen molecules. It allows the computation of Coulomb and exchange lattice sums to their asymptotic limit, and renders obsolete the empirical procedure of guessing the number of interactions to be included in the calculations.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400854
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    The Ab-Initio hybrid crystal orbital/molecular cluster approach to study the electronic structure of molecular crystals and reactions in the solid environment (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 619-628 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hybrid method having features of ab-initio crystal orbital and ab-initio molecular cluster methods is proposed. In the approach presented the molecular crystal is treated as an infinite chain in a direction z, while two other directions are simulated by finite interactions of the molecular type. The new approach is especially useful for an investigation of anisotropic crystals. Test calculations for the carbon dioxide crystal are presented. The method was also employed for the investigation of a dissociation pathway of C—N bond in nitromethane in nitromethane crystal.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400855
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    Theoretical properties of a 3-layer film of LiBeH3 (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 629-639 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The linear combinations of Gaussian-type orbitals-fitting function (LCGTO-FF) technique has been used to calculate the binding energy and electronic band structure of a 3-atom-thick film extracted from bulk LiBeH3 in the cubic perovskite structure. The film is composed of an interior layer of LiH sandwiched between two exterior layers of BeH2, i.e., there are eight atoms per unit cell (1 Li, 2 Be, and 5 H). The calculated cubic lattice parameter for the 3-layer (a = 5.74 au) lies roughly midway between the previously published theoretical lattice parameters for a BeH2 monolayer (5.51 au) and bulk LiBeH3 in the cubic perovskite structure (5.89 au). The 3-layer film is predicted to be a semimetal (i.e., zero-gap semiconductor), unlike both bulk LiBeH3 which is predicted to be a semiconductor, and monolayer BeH2, which is predicted to be a good metal. The metallic nature of the 3-layer is due to a Be surface state that cuts across the other valence bands of the film, in good agreement with an earlier prediction that cubic perovskite LiBeH3 cleaved to expose a BeH2 layer would provide a metallic surface on an insulating substrate. The fact that the density of states goes to zero at the Fermi level is a direct result of the symmetries of the one-electron states.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400856
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    Dissociative adsorption and associative desorption of H2 on a flat surface (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 641-657 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A quantum mechanical time-dependent method was used to study the dynamics of dissociative adsorption and associative desorption of H2 on a flat, static surface. We used a two-dimensional model in which the molecular axis was held parallel to the surface and the diatom internuclear separation and distance above the surface were the dynamic variables. A modified London-Eyring-Polanyi-Sato (LEPS) potential described the molecule-surface interactions. The wave function for the molecule was represented by its values on a spatial grid of points. The wave function was propagated by expanding the time evolution operator in a series of Chebyshev polynomials and using the properties of the Fourier transform to calculate the kinetic energy. The computational requirements of the problem were significantly reduced by using an L-shaped grid which deletes a large number of points where it is known a priori that the wave-function amplitude vanishes. State-to-state transition probabilities were calculated as a function of the initial translational and vibrational energy for potentials with early, late, and intermediate barriers. The location of the barrier has a strong effect on the energy threshold for reaction and on the distribution of energy between vibration and translation in the products.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400857
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    Theoretical study on Al multiple substitutions in the MFI zeolite (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 659-669 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this work we deal with ab initio and semiempirical calculations of single and multiple Al → Si replacements in the ZSM-5 structure. Substitutional energies for single replacements were obtained for cluster models of monomers, hexamers, and for the secondary building unit (SBU) of the zeolite by means of nonempirical SCF calculations, as well as the modified neglect of differential overlap (MNDO) method for extended clusters. The choice of the semiempirical methods for the study of multiple Si replacements by Al in the extended cluster model of the SBU is justified from the results with monomers and hexamers where the replacement energies obtained with MNDO are qualitatively the same as those from ab initio calculations. According to the results, a site occupancy order in the unit cell of the ZSM-5 network is derived from multiple Al → Si substitutions in the SBU, providing a theoretical basis for the Loewenstein-Dempsey Al sitting avoidance rules. Likewise, a Si/Al limit ratio in the Mobil FIve (MFI) zeolite, along with the corresponding Al distribution pattern in the unit cell, are also obtained.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400858
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    Nonadiabatic calculations for tdμ relevant for muon catalyzed fusion (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 671-686 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Due to the mass effect, muonic molecular ions are about 200 times smaller than their electronic counterparts. The proximity of the nuclei in the tdμ ion results in fusion taking place within a picosecond. The properties of this ion are central to understanding the phenomenon of muon catalysis. We developed a computational method of solving the nonadiabatic Schrödinger equation for the bound and resonant states of tdμ and its isotopic analogues. The method takes into account both the Coulomb interactions and the strong nuclear forces responsible for the fusion reaction. The wave functions obtained from our method were used to predict very accurately branching ratios and transition rates relevant for various stages of the muon catalytic cycle. Knowledge of these quantities will guide the experiments and help to answer the question of feasibility of net energy production via muon catalysis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400859
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    Computation of scanning tunneling microscope images (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 687-702 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article describes the computation of the tunnel current in a scanning tunneling microscope (STM). The calculation accounts for the three-dimensional scattering taking place simultaneously in the first atomic layers of the sample and in the apex of the probing tip. The model is built with the following ingredients: (a) the tip is represented by a cluster of atoms attached to an otherwise planar, free-electron metal surface, and (b) the analyzed sample is a planar free-electron metal with a local potential corrugation induced by an isolated molecule or adatom. The potential barrier includes the strong bending effect due to the image-charge formation occurring as the tunneling electron crosses the gap between the tip and the sample. The specific theoretical approach designed to solve this scattering problem exploits the fast Fourier transform algorithm to construct a transfer matrix in a mixed real- and momentum-spaces representation. The total current is obtained by summing the contributions of all scattered waves traveling in the barrier between the tip and the sample, and it is studied in this article for various positions of the tip relative to the adsorbed atomic cluster. The theory is used here to simulate the scan of a model-aluminum atom on a free-electron metal substrate using electrons focused by a single-atom tungsten tip.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400860
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    Bonding in heteronuclear transition-metal diatomics: NbIr (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 689-698 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bonding in transition-metal molecules presents novel features: (i) s electron bonding is overcome by multiple d electron bonding, (ii) intraatomic exchange favoring atomic magnetization competes with bonding that tends to pair the electrons, and (iii) in the heteronuclear dimers, the ionic terms may be important due to strong charge-transfer effects. The NbIr heteronuclear diatomic molecule shows all these features clearly. The cellular multiple scattering-xαβ calculation presented in this paper shows the ground state to correspond to antiferromagnetic coupling between the highly magnetic Nb atom and the Ir atom. A one-electron charge transfer from Nb to Ir was found; the result is an ionic structure, Nb+Ir-, for the dimer. The computed equilibrium distance, 4.100 a.u., corresponds to a region where d bonding strongly overcomes the s bonding, which alone would have stabilized the molecule at 5.950 a.u. At intermediate interatomic separations, 5.35 a.u., the NbIr system has a state in which all molecular orbitals are bonding with a high hybridization between the ns and (n - 1)d electrons of each atom, resulting in a (almost entirely) covalent high multiple-bond formation for this meta-stable state of the dimer.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390506
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    Construction of orthogonal subspaces (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 747-754 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An orthogonalization procedure is presented that allows construction of at least (n-m) vectors orthogonal to {Xj}, j equals; 1, m, by linear combinations solely among {ηi}, i equals; 1, n, n〉m, and 〈Xj/ηi〉≠0. An important application of the procedure is in effective core potential methods for which valence orbitals can be constructed that are orthogonal to the core orbitals and yet involve no component of the core. Thus, a separate calculation for only the valence electrons can be performed without any explicit reference to the core electrons (orbitals).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390510
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    Quasi-particle equation from the configuration-interaction (CI) wave-function method (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 225-242 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Green-function method is a well-known way to reduce the quantum mechanical problem of n electrons moving in the field of clamped nuclei to the problem of solving a one-electron Schrödinger equation (the quasi-particle equation) involving a pseudopotential (the self-energy). This method is widely used in solid-state, low-energy electron-molecule scattering, ionization, and electron attachment theory, and much work has focused on finding accurate self-energy approximations. Unfortunately, the operator nature of the fundamental quantity (Green function) in the usual quasi-particle equation formalism significantly complicates the derivation of self-energy approximations, in turn significantly complicating applications to inelastic scattering and multiconfigurational bound-state problems. For these problems or wherever the operator approach becomes inconvenient, we propose an alternative quasi-particle equation derived wholely within a configuration interaction wave-function formalism and intended to describe the same phenomenology as does the Green function quasi-particle equation. Our derivation refers specifically to electron removal but is readily generalized to electron attachment and scattering. Although the Green function and wave-function quasi-particle equations are different, we emphasize the parallels by rederiving both equations within the equations-of-motion formalism and then producing a wave-function analog of the Green function two-particle-hole Tamm-Dancoff approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400206
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    1991 Sanibel symposia list of participants (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. ix 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400704
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    Effect of proton transfer on neighboring hydrogen-bond strength (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 37-48 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transfer of a proton from A to B in AH+‥B‥C to form A‥+HB‥C is expected to enhance the binding energy of C to the remainder of the H-bonded chain since C is now adjacent to a charged ion rather than to a neutral molecule. But since the actual proton motion between A and B is typically only 1 Å or so, the interaction should be considerably less than that in isolated +HB‥C. Ab initio calculations with a variety of basis sets are used to quantitatively measure the enhancement of this binding energy. Systems investigated include the homotrimers of water and of ammonia, ammonium-formate-water, and formic acid-imidazole-water.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400709
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    Biographical sketch of Michael KashaInstitute of Molecular Biophysics and Department of Chemistry, Florida State University, Tallahassee, Florida 32306-3015 (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 235-250 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390304
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  • 143
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    Solvent effects in dense gases (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 399-409 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of perturber gases, partial pressures in the range 0-50 atm, on the absorption spectra of high-n Rydbergs, n ≥ 10, in methyl iodide and benzene have been investigated. The perturbers were rare gases and H2. It has been shown that the spectroscopic energy shift Δ = Δ(ρ, n) is given by Δ = Δ°ρ, where ρ is the number density of the perturber, for n ≥ 10. The shift data can be interpreted using a Fermi model, and values of scattering lengths for perturbers can be extracted. These scattering lengths are internally consistent, independent of the absorber, and in excellent agreement with electron-swarm results. Given that the Fermi model is nonspecific and microscopic, scattering shifts and lengths for mixtures of perturber gases can be predicted. These predictions, having been verified by experiment for He/Ar mixtures, provide a means of “tailoring” any required scattering length. Finally, it is shown empirically that the determinative scattering parameter is the polarizability of the perturber, and a universal relationship a = -0.26α + 1.18 between scattering length a, in Bohr radii, and polarizability α is found to exist.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390316
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  • 144
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    The intermolecular vibrations of the bifurcated water dimer: An Ab initio study (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 449-454 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The intermolecular modes of the bifurcated water dimer are determined at the HF level using an extended basis set. In these computations, the donor libration frequency is found to be real and the bifurcated structure does not collapse toward the linear dimer. This result is contrary to all previous ab initio computations, which have predicted a Hessian with one negative eigenvalue. A good representation of other intermolecular modes, such as the libration of the acceptor, also requires an extended basis set. An interesting infrared active transition is predicted around 444 cm-1. This transition, which corresponds to the donor wag, is found in the low-temperature spectrum of water in a N2 matrix.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390320
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  • 145
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    Masthead (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390401
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  • 146
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    String model for the rate constant of nonadiabatic solvation in the hydration reaction of carbon dioxide (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 561-583 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Perturbation theory for the rate constant of nonadiabatic solvation is presented. Miller's treatment of the RRKM theory is used for the unperturbed rate constant, and thereby the “string model” of chemical reaction is used for the description of the perturbation of solvation. The reaction path under the influence of the external force field is defined as the intrinsic reaction coordinate (IRC) that is treated as a string. The string is thrown in the external static force field that acts as a nonadiabatic source of perturbation. As an application of the present treatment, the effect of the external point charge for hydration reaction of CO2 is calculated as a preliminary model for catalytic activity of the carbonic anhydrase in the tissues and lung capillary vessels.
    Additional Material: 15 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560390404
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  • 147
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    Approximate noninteracting kinetic energy functionals from a nonuniform scaling requirement (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 379-388 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have recently proven an inequality for the exact noninteracting kinetic energy density functional \documentclass{article}\pagestyle{empty}\begin{document}$ T_s [n]:\mathop {\lim }\limits_{x \to \infty } T_s [n_\lambda ^x] \le T_s [n_s^y [n] + T_S^2 [n] 〈 \infty,where{\rm }n_\lambda ^x (x,{\rm }y,{\rm }z) = \lambda n(\lambda x,{\rm }\lambda {\rm y, }\lambda z) $\end{document}. It is known that the gradient expansion through fourth order, TsGE[n], violates this inequality. Toward improving TsGE[n], we have constructed two new functionals, Ts1[n] and Ts2[n], by keeping the zeroth and second orders in TsGE[n] and replacing the fourth order with two simple terms, respectively, so that these new functionals satisfy the inequality. Numerical tests are presented for Ts1[n], Ts2[n], and TsGE[n] and for the gradient expansion through second order. Hartree-Fock and hydrogenic atomic densities are employed.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400309
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  • 148
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    Erratum: Dirac-Fock self-consistent field method for closed-shell molecules with kinetic balance and finite nuclear size (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 429-432 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400315
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  • 149
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    Masthead (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400401
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  • 150
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    A quantum chemical investigation of pyrolysis reactions of glyoxylic acid ethylester (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 491-500 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two possible reaction paths for the pyrolysis of the ethylester of glyoxylic acid have been studied by ab initio molecular orbital calculations. The basis sets 3-21G and 6-31G* have been used, and electron correlation has been included by Møller-Plesset calculations up to fourth order. Our calculations indicate that the reaction leading to acid and ethylene through a 6-membered ring transition state is favored relative to a process involving a formyl hydrogen transfer via a 5-membered ring to the alkyl unit leading to ethane, CO, and CO2. The predicted activation energies for these two reactions obtained at the highest level of calculation, MP4(SDTQ)/6-31G*, are 50.4 and 71.7 kcal/mol, respectively. The transition states have RHF wave functions that are stable relative to UHF solutions using the 3-21G basis. The geometry of the transition states and IRC following indicate that both reactions are strongly asynchronous: The C—O bond rupture is virtually completed before hydrogen transfer occurs. For comparative purposes, analogous calculations have been performed for the ethylester of formic acid, where it is confirmed that a 6-membered ring transition state is preferred relative to a 4-membered one by around 42 kcal/mol at the highest level of calculation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400405
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  • 151
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    A time-dependent molecular orbital approach to electron transfer in ion-metal surface collisions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 545-558 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A time-dependent molecular orbital method has been developed to study charge transfer in collisions of ions with metal surfaces at energies between 1 and 100 au. A set of localized basis functions consisting of generalized Wannier functions for the surface and s- and p-atomic functions for the ion, is used to separate the system into primary and secondary regions. An effective Hamiltonian and time-dependent equations for the electron density matrix are obtained in the primary region, where most charge transfer occurs. The equations for the electron density matrix are solved with a linearization scheme. The method is suitable to study atomic orbital orientation for collisions of ions and surfaces. A model calculation for Na+ + W(110) collisions with a prescribed trajectory is presented. The interaction potentials between the W(110) surface and Na+ 3s and 3p orbitals are calculated from Na+ pseudopotentials. Results show that the yield of neutralized atoms in 3p states changes as the collision energy is lowered.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/qua.560400409
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  • 152
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    On the conditions for physical admissibility of Schrödinger wave functions (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 605-609 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that the dispute about the conditions for physical admissibility of Schrödinger wave functions may be settled if the following two questions are clarified: (a) Are these condittions rooted in the foundations of quantum mechanics or invoked only for particular physical models? (b) Do we consider either the position-space wave function or the momentum-space wave function? Both the case of closed states and scattering states are considered. Some general remarks about these conditions are made in the Conclusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400504
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  • 153
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    Origin of apparent swain-schaad deviations in criteria for tunneling (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 361-366 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Vibrational analysis calculations have been conducted in an effort to understand the origins of apparently anomalous relationships reported between kH/kT and kD/kT kinetic isotope effects. The actual isotopic substitutions used in previous work are more complex than a simple comparison between H/T and D/T isotope effects. The relationships between the actual isotope effects determined in these studies amount to tests of two standards of conventional isotope effect theory, the rule of the geometric mean (or the lack of isotope effects on isotope effects) and the Swain - Schaad rule. Model calculations illustrate the importance of violations of the rule of the geometric mean (over Swain - Schaad deviations) arising in models that incorporate both explicit reaction-coordinate coupling of two isotopic sites and reaction-coordinate tunneling. Implications for experimental studies of turneling using apparent Swain - Schaad exponents are discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040607
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  • 154
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    The schiff base between pyridoxal-5′-phosphate (PLP) and hexylamine. Formation of the unprotonated form of the imine by reaction of the unprotonated PLP and free amine (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 372-380 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Electrochemical and spectrophotometric studies of the pyridoxal-5′ -phosphate hexylamine Schiff base (PHSB) in strongly basic media were carried out. The equilibrium constant and rate constants of the formation and hydrolysis of the unprotonated imine from the unprotonated pyridoxal-5′ -phosphate and free amine were determined by linearscan cyclic voltammetry. The acid-base dissociation constant of the imine group was obtained by spectrophotometric measurements. Absorption bands for the free imine and the conjugate acid are characterized by a log-normal distribution. These studies are for general application to the quantitative characterization of non-enzymatic model compounds.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040609
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  • 155
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    Factors affecting the reversibility of the electrophilic step in olefin bromination. The case of 5H-dibenzo [a, d] cycloheptene (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 387-398 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The tendency of ion-pair intermediates generated by treatment of trans-10-bromo-10, 11-dihydro-11-hydroxy-5H-dibenzo [a, d] cycloheptene (5) with HBr to release Br2 giving 5H-dibenzo [a, d,] cycloheptene (1) has been evaluated. The observed 9:1 ratio between ion-pair collapse to the trans-dibromide (7) and Br2 release to olefin 1, as compared with the 3:7 ratio found with the 5H-dibenz [b, f] azepine-5-carbonyl chloride system, has been interpreted as indicating a much lower propensity for reversibility of ion-pair formation in the bromination of 1. The structural parameters obtained by x-ray diffraction of the dibromide 7 show for this compound an angle strain at C-10 and C-11 analogous to that found in trans-10, 11-dibromo-10, 11-dihydro-5H-dibenz [b, f,] azepine-5-carbonyl chloride. Olefin 1 adds Br2 in 1,2-dichloroethane at 25°C according to a third-order rate law, with k3 = 30(3) M-2 s-1. About 10% of 5-bromo-5H,-dibenzo [a, d] cycloheptene, arising from collapse of a dibenzo [a, d] tropylium ion intermediate (9), is formed in this reaction besides the expected trans-dibromide 7. Spectral evidence for the formation of 9, arising by rearrangement of a first formed weakly bridged ionic intermediate in the reaction of 1 with Br2, is presented. the results obtained with the 5H-dibenzo [a, d,] cycloheptene system have been rationalized on the basis of the formation of very weakly bridged intermediates having a much lower tendency to revert back to olefin and Br2 with respect to the corresponding symmetrically bridged bromonium ions.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040611
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  • 156
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    SRN1 Reactions of nucleophiles with radical clocks: Rate constants for some radical-nucleophile reactions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 404-412 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Treatment of o-3-(but-3-enyloxy)benzene (1) with anions -SPh, -PPh2 and -PO(OEt)2 in ammonia, acetonitrile or dimethyl sulphoxide gives both direct substitution and cyclized products. The formation of the latter confirms the intermediacy of the o-3-(but-3-enyloxy)phenyl radical (2) and confirms that the reactions follow the SRN1 pathway. The kinetics of the coupling of the aryl radical 2 were determined by comparison with the known rate of cyclization of 2. Similar experiments with the neopentyl bromide, 6-bromo-5,5-dimethylhex-1-ene, and its 3-oxa derivative also gave cyclized and uncyclized products, thus confirming that the SRN1 mechanism applies to the reactions. Approximate rate constants for the coupling of a neopentyl radical with the nucleophiles -SPh and -PPh2 have thus been determined.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040703
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  • 157
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    Short Communications. Biphenyl-3,4′-Dinitrene (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 459-462 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Photolysis of biphenyl-3,4′ -diazide in a rigid glassy matrix at 77 K yields quintet state biphenyl-3,4′ -dinitrene with zero-field splitting parameters of |D/hc- = 0.153 cm-1 and |E/hc| = 0.019 cm-1 determined by electron spin resonance spectroscopic studies. Curie plot studies are consistent with assigning the quintet to be the ground state in this species. This finding confirms qualitative connectivity-based predictions for this general connectivity type of openshell system, and is in qualitative agreement with spectral INDO-CI computational predictions for both planar and twisted geometries of the dinitrene.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040708
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  • 158
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    The α-bromocyclohexanone ring: The relationship between its conformation and the ultraviolet and infrared absorption of the keto group (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 420-438 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of diterpenoids whose C-ring was an α-bromocyclohexanone showed a discontinuity in the relationship between the Br—C—C=O torsion angle and the Br…O contact distance at about 50°, below which the Br…O distance remained effectively constant at about 3.0 Å. This effect is caused by the non-compressibility of the van der Waals radii of the Br and O atoms. Analysis of the parameters for all compounds in the Cambridge Data File containing an α-bromocyclohexanone ring confirmed this phenomenon. Once the Br…O distance approaches 3.0 Å, the Br—C—C and C—C=O angles are forced open to accommodate the Br…O compression strain as the torsion angle is further reduced. An approximate value of the Br…O distance, d in Å, can be estimated for any torsion angle, ø, by the empirical equation d2 = R - S cos φ + T cos2 φ where R = 11.73, S = 3.62 and T = 0.75. There is a linear relationship between the Br…O separation and both the infrared vibration frequency v and the ultraviolet absorption wavelength δmax of the C=O group: the greater the distance, the lower is the frequency v and longer the wavelength δmax. Thus measurement of the ultraviolet and infrared spectra of a compound containing an α-bromocyclohexanone system can yield information about the Br…O distance and hence the conformation of the six-membered ring. There are also systematic trends in the effect on the spectroscopic properties of the keto group that accompany changing the halogen from fluorine through to iodine. When the halogen is axial, its electronegativity has a maximum influence on the C=O vibration frequency by a ‘through-bond’ inductive process. When the halogen is equatorial, it exerts a steric compression on the non-bonded electrons in the 2p orbital of the oxygen atom. This enhances hybridization to the sp2 state and this simultaneously strengthens the C=O bond and enlarges the n → π* energy gap. This ‘through-space’ influence is simply a process of steric compression, dependent on the size of the halogen atom. It accounts well for all of the systematic trends in both infrared and ultraviolet frequencies of the C=O group when the halogen is equatorial and eclipses the C=O bond.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040705
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  • 159
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040801
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  • 160
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    Treatment of electrostatic effects within the molecular mechanics method. 3. Double bonds and conjugated systems (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 467-478 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The previously developed general method (IDME), which includes calculation of electrostatic and solvation effects on conformational equilibria, has been extended to molecules containing double bonds and conjugated systems. It was applied in connection with MM2 studies to the calculation of the charge distributions and dipole moments, and to the conformational energies of some β-substituted cyclohexenes, exo-methylenecyclohexanes and benzocycloheptenes. Conformational equilibria and dipole moments were well calculated. It was concluded that electrostatic interactions do not play a major role in determining conformational preferences in these compounds. On the other hand, the energies of the preferred conformations of the ten-membered ring in (E)-3β-acetoxy-5,10-seco-1(10)-cholesten-5-one are poorly calculated without the IDME procedure, and fairly well with it.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610040802
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  • 161
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    Theoretical models for the reduction of arylmethyl halides by triorganotin hydridesPreliminary presentation of results at combined 45th Northwest-10th Rocky Mountain Regional Meeting of the American Chemical Society, Salt Lake City, UT, 13 June 1990. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 485-491 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two mechanistic pathways have been proposed for halogen atom transfer from the benzylic positions of halomethylarenes to triorganotin radicals. These are direct atom abstraction, which might involve an extremely polar transition state, and single electron transfer followed by bond cleavage. AM1 semi-empirical calculations have been utilized to model the rate-determining step of these processes. A wide range of related families of compounds have been studied, including substituted halomethylbenzes, selected halomethyl-substituted polycyclic aromatic hydrocarbons and oxygen- and nitrogen-containing chloromethyl-substituted heteroaromatic systems. Although these calculations are relatively simple, the present results corroborate the view that chlorine and bromine atom transfer from the benzylic position to triorganotin radicals involves a direct atom abstraction in the rate-determining step whereas reduction of the corresponding iodides proceeds via an electron-transfer mechanism.
    Additional Material: 8 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610040804
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  • 162
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    Ambident electrophilicity of alkyl aryl phosphates (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 516-522 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Hydrolysis of dimethyl aryl phosphates, (MeO)2P(O)OAr where the ArO group is derived from N-methyl-8-hydroxyquinolinium or 4-hydroxy-(N,N,N-trimethylanilinium) ion, proceeds with the cleavage of the P—OAr and Me—O bonds. The effect of external factors on the relative contributions of those two reaction pathways was studied. The increase in temperature favours, owing to the difference in activation entropies, the reaction at carbon. The addition acetone to the aqueous reaction medium slows down the reaction at carbon more rapidly than the reaction at phosphorus, indicating higher hydration requirements of the dealkylation transition state. In water-triffuoracetic acid mixtures only the P—OAr bond cleavage is acid catalysed; the catalytic effect is superimposed on the general, decelerating medium effect. Specific nucleophilic catalysis was demonstrated for the Me—O bond fission by thiosulphate ion (ca 60-fold acceleration), and for the reaction at phosphorus by fluoride ion (ca 500-fold acceleration).
    Additional Material: 6 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610040807
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  • 163
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040901
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  • 164
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    Short communication. Structural studies of bromine adducts of 1,2- and 1,4-bis(phenylseleno)benzenes. Evidence for the (TB, MC) structure of 1,2-(PhSeBr2)2C6H4 (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 523-525 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1,2-Bis(phenylseleno)benzene reacted with equimolar amount of bromine to yield a trigonal bipyramidal (TB) adduct, in contrast to the molecular complex (MC) structure of selenanthrene with bromine. Whereas the structure of 1,4-(PhSeBr2)2C6H4 was (TB, TB) at the two selenium atoms, that of the 1,2-derivative was demonstrated to be (TB, MC), the first example of an MC structure of PhSeC6H4Y with Br2 [Y = 2-PhBr2Se(TB)]. Both electronic and steric effects of the group must play an important role in MC formation. Rapid structural exchange in this tetrabromide, (TB, MC) ⇄ (MC, TB), was also observed.
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    Conformations of pentan-1-OL, hexan-1-OL and their thio analogues (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 536-540 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Empirical linear relationships between standard Gibbs free energy, ΔG298°, and parachor and between standard entropy, S298°, and parachor are presented for the aliphatic series H(CH2)nX with X = CH3, CH=CH2, C≡CH, Cl, OH, SH, SCH3 and SC2H5. In the series with X = OH and SH significant deviations of points for n = 4 and 5 are observed. INDO quantum-chemical analysis points to the formation of cyclic conformers of butan-1-ol, pentan-1-ol and their corresponding thio analogues. The formation energy of the cyclic conformers (higher for thiols than for alcohols) is proportional to the sum of deviations from the linearity of the points under discussion.
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    Review commentary. Solvation, the electrophilic driving force of ionic bromination of ethylenic compounds. The addition-solvolysis analogy (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 527-535 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solvation is the main driving force of electrophilic bromination since it is impossible to obtain a bromonium ion from bromine and alkene in the gas phase, whereas it is a very fast reaction in solution. The role of a protic solvent in this addition was investigated experimentally by extended Winstein-Grunwald relationships, kinetic solvent isotope effects and R, the rate ratios in two solvents of similar ionizing powers but different nucleophilicities. It is shown that electrostatic medium effects and electrophilic assistance to bromide ion departure are the main rate-determining factors of the reaction. These two contributions are roughly independent of the double bond substituents. Nucleophilic solvent assistance to positive charge development is also found; however, it provides only a small acceleration, the magnitude of which depends on alkene structure. This nucleophilic solvent involvement is annulled when crowded substituents inhibit approach of the solvent to the cationic part of the transition state or when positive charge is delocalized by conjugated electron-donating groups. These several solvent roles are identical in nature and in magnitude with those observed in heterolytic solvolysis. In halogenated solvents, the driving force of bromination arises from catalysis by a second bromine molecule which assists heterolysis of the bromine-bromine bond, leading to the bromonium-tribromide ion pair. Similar halogen catalysis occurs also in some solvolyses. Finally, return is also found in both reactions; reversible formation of bromonium ions is observed when their nucleophilic attack, the productforming last step, is made energetically difficult either by steric inhibition or by poor nucleophilicity of the trapping nucleophiles. Similarities and differences between electrophilic bromine addition and limiting solvolysis are discussed in terms of respective intermediate stabilities and heats of formation.
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    Photochemical transformations. 49.For Part 48, see Ref. 1. Solvent effects on singlet ionic and triplet photoreactions of some bridged polycyclic chlorides: Comparison with ground-state reactionsDedicated to Professor Kurt Schaffner on his 60th birthday. (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 541-546 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Direct irradiations of 2-chloro-6,7 : 8,9-dibenzotricyclo [3.2.2.02,4] nona-6,8-diene (5-Cl) were conducted in cyclohexane, acetic acid and wet acetonitrile. The products are 1-methylfluoranthene (8) in all three solvents, the allylic chlorides 8-chloro-7-methylene-2,3 : 5,6-dibenzobicyclo [2.2.2] octa-2,5-diene (3-Cl) and 7-chloromethyl-2,3 : 5,6-dibenzobicyclo [2.2.2] octa-2,5,7-triene (2-Cl) in acetic acid and acetonitrile and solvolysis product amides in wet acetonitrile. Compound 5-Cl had previously been shown to be the product of triplet sensitization of 2-Cl and 3-Cl, so that the singlet reaction reverses that of the triplet. The formation of 8 from 5-Cl was quenched with piperylene, whereas that of the allylic chlorides was not. Quantum yields of products and singlet lifetimes in the three solvents were measured. The solvent effects are discussed. Deuterium-labeling results on the formation of 5-Cl from 2-Cl and of 8 from 5-Cl are reported.
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    Steric effects of alkyl groups: A ‘cone angle’ approach (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 611-617 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A ‘cone angle’, θR, is defined for an alkyl group (R), which is proposed as a measure of the steric effect exerted by the group. The θR values for some 57 groups have been calculated mathematically by constructing the corresponding Corey - Pauling - Koltun molecular models. The variation in θR with the bulk of a group is satisfactory. However not all types of alkyl groups can be accommodated in this cone angle approach. In the case of the groups for which the cone angle can be measured, correspondences between θR and the two existing steric parameters (Taft's Es scale and Dubois' E′s scale) have been established. For some 23 alkyl groups θR has been used to explain the variation in the rate constant of the base-catalysed hydrolysis of RCOOEt with the nature of R. Our studies independently substantiate the basic assumptions of the Taft - Ingold hypothesis that, while the base-catalysed ester hydrolysis is mostly controlled by the steric and electronic effects of the R group, the acid-catalysed one is controlled almost solely be the steric effect.
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    Effect of hexadecyltrimethylammonium bromide micelles on the hydrolysis of substituted benzoate esters (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 13-18 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The alkaline hydrolysis of nine para-substituted phenyl esters of para-substituted benzoates was studied in the presence and absence of hexadecyltrimethylammonium bromide (CTAB) micelles. The second-order rate constant for alkaline hydrolysis in CTAB micelles (K2m) was calculated using a pseudo-phase ion-exchange model. the substituent effect on the second-order rate constant in the aqueous phase (k2w) and on k2m was analysed using Hammett's σ ρ plots. The calculated ρ values in micelles were 0.8 unit. larger than those in water. The effective low dielectric constant in the micellar surface may be responsible for the general effect of increasing the sensitivity of reactions to the electronic effect of substituents in micelles.
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    1,5-Sigmatropic shifts of bromine over a cyclopentadiene ring (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 31-47 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intrinsic mechanism of circumambulatory rearrangements of 5-bromo-5-methyl-1,2,3,4-tetramethoxycarbonylcyclopentadiene, 5-bromo-1,2,3,4 5-pentamethoxycarbonylcyclopentadien and 5-bromo- 1,2,3,4,5-pentaphenylcyclopentadiene due to sigmatropic shifts of bromine over the cyclopentadiene ring was proved, using the dynamic 13C and 1H NMR technique, to be governed by successive intramolecular 1,5-sigmatropic shifts. Semi-empirical AM1 and MINDO/3 calculations of reactions paths performed for fluoro-, chloro- and bromocyclopentadienes are in accord with the conclusion of a preference for a 1,5- over a 1,3-shift reaction path of halogen migration over a cyclopentadiene system. Intramolecular 1,5-sigmatropic shifts of chlorine in 5-chloro-5-methyl-1,2,3,4-tetramethoxycarbonylcyclopentadiene with the free energy barrier of ΔG298+ = 26.1 kcal mol-1 were studied using 1H NMR spectroscopy.
    Additional Material: 7 Ill.
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040201
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    Specific micellar rate effects on unimolecular decarboxylation and cyclization (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 71-76 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion and cyclization of o-3-halopropyloxyloxyphenoxide ion (PhY7) (Y = Br, I) are accelerated by aqueous cationic and zwitterionic micelles. For cationic micelles the rate enhancements (kM′kW′) increase with increasing bulk of the surfactant head groups but are largest for decarboxylation. There are good linear free energy relationships between micellar effects on these reactions and the plots of log kM′ for cyclization against log kM′ for decarboxylation have slopes of 0.46 and 0.64 for Y = Br and I, respectively. Surfactants that have twin tail or tri-N-alkylbenzyloxy head groups do not fit the relationship. Despite mechanistic differences between decarboxylation and cyclization (an intramolecular SN2 reaction), similar factors control micellar effects on these reactions. In the absence of surfactant there is only a qualitative relationship between free energies of activation of cyclization and decarboxylation in different solvents.
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    Aromaticity as a multi-dimensional phenomenon (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 163-169 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The classification of aromaticity criteria is studied. New aromaticity criteria are developed and discussed. A statistical analysis of such criteria is presented and compared with a similar analysis of the recent literature. It is shown that aromaticity is at least a two-dimensional phenomenon. The classification of the compounds depends on the type of criteria included in the analysis.
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    AB initio MO study of the halogen cation basicities of some organic bases (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 177-191 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Hartree - Fock calculations were performed to investigate the structure and relative stabilities of complexes between halogen cations and first- and second-row bases. It is shown by means of both a qualitative perturbation molecular orbital treatment and a topological analysis of the electronic charge density that second-row bases present enhanced halogen cation basicities compared with first-row bases. In this respect the results predict that although the fluorine cation basicity of water is smaller than its proton affinity, the fluorine cation basicities of SH2, thioether, phosphine and trimethylphosphine are considerably higher than their proton basicities. Similarly, phosphine and trimethylphosphine should have chlorine cation basicities greater than their proton affinities, in contrast with ammonia and trimethylamine. The results also show that fluorine and chlorine cation basicities are more sensitive to methyl substitution than proton affinities.
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    Micellar effects on the alkaline hydrolysis of N-alkyl-4-cyanopyridinium ions. An example of micelle-induced regiochemical selectivity (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 207-216 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rates of the reaction of N-alkyl-4-cyanopyridinium (RCP) ions [alkyl = CH3 (MCP), n-C4H9 (BCP), n-C8H17 (OCP), n-C12H25 (DCP)] with OH- ion in water are independent of chain length and RCP concentration up to 0.001 M. The ratios of the concentrations of the reaction products, N-alkyl-4-pyridone (P) and N-alkyl-4-carboxamidopyridinium (A), P/A, are similar for all substrates. In water the P/A ratios increase with pH, reaching a plateau value of ca 2 at pH ≥ 13. Added salts slightly decrease the reaction rate and do not affect the P/A ratios. In aqueous solutions, addition of dioxane increases both rates and P/A ratios. Micelles of hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide; CTAB) and 3-(N,N-dimethyl dodecyl ammonium)propane-1-sulphonate (SDP) catalyse the alkaline hydrolysis of OCP and DCP and increase the yield of pyridone with BCP, OCP and DCP. In micellar CTAB and SDP the attack of OH- on RCP occurs almost exclusively at the 4-position of the pyridinium ring. Sodium dodecyl sulphate micelles inhibit the reaction and produce small changes in the P/A ratio. The regiochemical selectivity produced by micelles, leading to a preference for the attack of OH- at the pyridinium ring, was rationalized in terms of the low effective dielectric constant at the micelle-water interface.
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    URL: http://dx.doi.org/10.1002/poc.610040403
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    Structure, topological electron density analysis and aromaticity of 4-heterosubstituted methylenecyclopropenes: X= X=CH2, NH, O, SiH2, PH and S (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 242-250 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The structures of a series of heterosubstituted methylenecyclopropenes and methylenecyclopropanes were optimized at the HF/6-31G* level. All methylenecyclopropenes are planar except for the silicon analogue, which is bent at both C-3 and Si. The planar silicon structure is a transition state. The relative aromaticity of these compounds were evaluated using the C-1—C-3 bond length, the integrated charge on C-3 and the heteroatom, and delocalization energy. Second-row systems have slightly larger delocalization energies than their first-row counterparts, owing to their larger polarizability. Using these criteria, methylenecyclopropene and the silicon analogue are not aromatic and the N, O, P and S analogues are moderately aromatic. The planar silicon analogue is antiaromatic and bends from planarity to reduce this antiaromaticity.
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    Kinetics and mechanism of the alcoholyses of ethyl fluorosulphate (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 251-259 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The alcoholyses of ethyl fluorosulphate in methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl and n-pentyl alcohols in the initial concentrations and temperature ranges of (1-10) 10-3 M and - 15.00 to 22.00 °C, respectively, were studied. The reactions follow pseudo-first-order kinetic laws up to at least ca 75 per cent ester conversions. At 10°C the experimental rate constant for ethanolysis is similar to that of ethyl triflate but much smaller than for its hydrolysis. The reactivity of the ester is ca 104-105 times higher than that of alkyl halides and benzenesulphonates. In alcohol-benzene and alcohol-acetone mixtures the ΔH≠ and ΔS≠ activation parameters are only slightly affected by the media composition. The effect of the ‘lyate ion’ on the kinetics of these reactions were investigated and the effects of changes in the dielectric constant of the media were evaluated. It is concluded that the alcoholyses of the ester fulfil the requirements for predominant SN2-type mechanism, where the reaction ground states are more polar than the corresponding transition states.
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    NMR study of polycrystalline azoles (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 271-276 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polycrystalline pyrazole, imidazole and benzotriazole were investigated by 1H and 2H NMR spectroscopy. In addition to the usual broad line of the 1H NMR signal due to the dipole-dipole interaction, a significantly narrowed component (δν = 1-2 kHz) of a complex triplet structure was detected in all three compounds. To interpret this observation, a mechanism with virtually complete averaging of the dipole-dipole interaction for a small part of the sample protons is suggested. The mechanism is based on proton interaction with the unpaired electron of a short-lived radical of the type Az· or (H-Az·-H).
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    Gas-phase acidity of some α-keto aldoximes: Experiment and theory (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 285-292 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Experimental gas-phase acidities of 2-oxopropanaloximes, XCH2COCH=NOH (X = H, CH3S, CH3SO, CH3SO2; compounds 1-4), were determined by Fourier transform ion cyclotron resonance (FT-ICR) spectrometry. The values are δ Gacid° = 1401, 1381, 1360 and 1351 kJ mol-1 for 1, 2, 3, and 4, respectively. Molecular orbital calculations using the semi-empirical AM1 method provided information on the geometry and relative energy of neutrals species 1-4 and their conjugate bases, together with charge distributions and entropies of deprotonation. It is demonstrated that the proton abstraction occurs preferentially at the oxime function; the formation of an enolate as a conjugate base is unfavourable by 70-140 kJ mol-1. The large variation of the gas-phase acidities for 1-4 is explained in terms of the field/inductive empirical substituent constant σF. The variation of solution acidities appears to be comparatively strongly attenuated. This attenuation is attributed mainly to charge delocalization in the anion, which was confirmed by charge density calculations.
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    Depurination of (dien)Pt(II) complexes of purine deoxyribonucleosides. Comparison with the effects of (dien)Pd(II) ion complexing (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 301-309 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: First-order rate constants for the hydrolytic depurination of 2′-deoxyinosine and its various (dien)Pt(II) ion complexes were measured over the acidic pH range. The rate profiles obtained indicate that the uncomplexed nucleoside and its N1-(dien)Pt(II) complex are depurinated via mono- and di-protonated species, whereas the N7-(dien)Pt(II) and N1, N7-di(dien)Pt(II) complexes exhibit significant spontaneous hydrolysis, which competes with a markedly retarded acid-catalysed reaction. Rate constants for the various partial reactions were calculated and the results were employed to explain the effects that (dien)Pd(II) ion exerted on depurination rates of the same compounds. Similar measurements were carried out with the N1, N7-di(dien)Pt(II) complex of 2′-deoxyadenosine in order to further the understanding of the previously reported rate-enhancing effect of (dien)Pd(II) ion on the depurination of 2′-deoxyadenosine.
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    Crystallographic studies of intra- and inter- molecular interactions. Part VI. Crystal and molecular structure of N,N′-dimethyl-N′-phenylsulphonylformamidine. Equalization of CN bond lengths in the amidine fragment as a result of substituent effects due to push-pull (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 331-335 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The crystal and molecular structure of N,N-dimethyl-N′-phenylsulphonylformamidine is solved by direct methods and refined to R = 0.041 for 935 reflections, Equalization of CN bond lengths in the amidine fragment is discussed in terms of a push - pull effect operating between the N,N-dimethyl and SO2Ph groups. A significant role of the substituent at the functional carbon on the degree of π-electron delocalization on the NCN fragment is interpreted by use of the HOSE model.
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    Orientation of benzoic acid and terephthalic acid on an alumina surface and their reactivities observed by infrared spectroscopy (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 346-352 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The orientation of benzoic acid and terephthalic acid on alumina was ascertained by IR measurements. Benzoic acid was chemisorbed as a carboxylate anion with a vertical conformation of the benzene ring (0 〈 θ 〈 1.0) and as a mixture of the anion and the acid (1.0 〈 θ). Terephthalic acid was chemisorbed as a mixture of monocarboxylate anion (hydrogenterephthalate) and dicarboxylate anion (0 〈 θ 〈 0.3), as the monocarboxylate anion with a vertical conformation of benzene ring (0.3 〈 θ 〈 1.0) and a mixture of the monocarboxylate anion and terephthalic acid (1.0 〈 θ). The carboxyl group of expected hydrogenterephthalate adsorbed through the carboxylate anion on alumina (θ = 0.8 : 0.37 mmol g-1 alumina) readily reacted with dimethyl sulphate to form monomethyl terephthalate selectively.
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    Influence of some steric and electronic effects on the mechanism of SNAr reactions in dimethyl sulphoxide (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 367-371 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactions of 1-chloro- and 1-fluoro-2,4-dinitrobenzenes with aniline and 4-methylaniline in dimethyl sulphoxide are not base catalysed. When the nucleophile is 2-methylaniline, the reaction of the fluoro compound is base catalysed whereas that of the chloro compound is not. The reactions of 1-bromo-2-fluoro- and 1-bromo-2-chloro-3,5-dinitrobenzenes with both aniline and 2-methylaniline are not base catalysed. These results indicate that, in certain cases, the incidence or absence of base catalysis in aromatic nucleophilic substitution (SNAr) reactions in dipolar aprotic solvents results from an interplay of steric and electronic factors as they affect the magnitude of the (k2 + k3 [B])/k-1 ratio.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040608
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  • 184
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    Controlling factors determining addition and reduction products in the grignard reaction of substituted benzophenones, acetophenone and fluorenone with ‘EtMgBr’ (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 381-386 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Addition (Add.) vs reduction (Red.) products in the reactions of substituted benzophenones, acetophenone and fluorenone with ‘EtMgBr’ were compared in diethyl ether, 1,2-dimethoxyethane and tetrahydrofuran. Plots of log (Add./Red.) vs σ-values or the oxidation potentials of ketones showed characteristic upward curves depending on the polarity of the solvents. The results are discussed on the basis of both the combined effects of the stability of the monomeric radical ion pair and the dimeric radical ion pair derived from ketone and ‘EtMgBr’, and the well known Schlenk equilibrium of ‘EtMgBr’ in solutions.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040610
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  • 185
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    Micellar rate effects on reactions of hydroxide ion with phosphinate and thiophosphinate esters (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 618-628 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cationic micelles of cetyltrimethylammonium chloride, bromide and mesylate (CTACl, CTABr, CTAOMs) speed reactions of OH- with phosphinate and thiophosphinate esters: Ph2PO.OPh (1a), Ph2PO.OC6H4NO2-p (1b), Ph(i-Pr)PO.OC6H4NO2-p (1c), Ph2PO.SEt (2a), Ph2PO.SPh (2b), (EtO)2PO.SPh (2c) and (EtO)2PS.OC6H4NO2-p (Parathion, 3). First-order rate constants go through maxima with increasing [surfactant]. The rate - surfactant profiles are fitted quantitatively in terms of a kinetic model that treats the distribution of OH- between aqueous and micellar pseudo-phases in terms of coulombic and non-coulombic ion-micelle interactions. Second-order rate constants at the micellar surface are lower than in water by factors that range from 0.035 for 1a to 0.7 for 1c. The thiophenyl derivative (2b) is more reactive than the corresponding phenoxy derivative (1a) and it is more reactive than the corresponding thioethyl derivative (2a). Parathion (3) is the least reactive substrate in both water and micelles.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041006
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  • 186
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    Semiempirical SCF-MO calculations of kinetic isotope effects (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 635-638 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Carbon and deuterium kinetic isotope effects (KIEs) on the isomerization of methyl isocyanide were calculated by using the geometries and force fields obtained with MNDO, AM1 and PM3 Hamiltonians. These theoretical KIE values were compared with the corresponding experimental values. None of the hamiltonians used proved to be superior to any of the others. The best agreement for the carbon isotope effect was obtained by using the PM3 method; however, the deuterium isotope effect obtained by this method gave the poorest fit to the experimental data. The opposite is true when the MNDO Hamiltonian was used.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041008
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  • 187
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    Relationships between electronic substituent parameters (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 629-634 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Core-electron energies for sulphur in a series of 2-substituted thiophenes have been used to investigate the relationship between electronic substituent parameters as developed by Taft and Topsom and by Charton. Initial- and final-state energies are analysed in terms of familiar substituent effects, such as field, delocalization and polarizability. The results show that the data correlate equally well with both sets of parameters and that there are many common features between the two methods. Both agree that resonance delocalization contributes significantly to the initial state, but has virtually no effect on the final state. In connection with this investigation we have also correlated the parameters for 31 substituents that are parameterized in the two approaches. The results of this more general study indicate some real differences between these and suggest that neither of the parameterizations incorporates all the electronic effects.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041007
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  • 188
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    The effect of pressure on swern-moffatt oxidations (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 639-642 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rates of oxidation of cyclohexanol by dimethyl sulphoxide in conjunction both with acetic anhydride and with dicyclohexylcarbodiimide have been measured with variation of both temperature and pressure. Activation volumes were found to be -25 and -34 cm3 mol-1, respectively, and the absence of an α—d PKIE was noted. The reaction mechanism is discussed in the context of these values.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041009
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  • 189
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    Electronic Resource
    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041101
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  • 190
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    Short communication. Synthesis and properties of 4-cyano-1-(7-carboxyheptadecyl)pyridinium bromide: A probe of the ionic composition near the surface of positively charged micelles (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 643-646 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 4-Cyano-1-(7-carboxyheptadecyl)pyridinium bromide (CCHP) was synthesized using standard procedures. The rates and product distribution of the reaction between OH- ion and CCHP are very similar to those previously obtained with alkyl-substituted 4-cyanopyridinium ions. The effect of hexadecyltrimethylammonium bromide micelles on the rate and product distribution of CCHP indicated that the cyanopyridinium ring of this compound is distal to the surface of the micelle. CCHP constitutes a probe for ionic composition in the vicinity of positively charged micelles.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041010
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  • 191
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    Molecular mechanics (MM3) calculations on disulfides (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 659-666 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An MM3 parameter set was developed for disulfides so as to permit the force field representation of these molecules with respect to geometries, including conformations, vibrational spectra and heats of formation.
    Additional Material: 13 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041103
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  • 192
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    Molecular Mechanics (MM3) calculations on sulfides (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 647-658 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The structures of eleven sulfide compounds including methanethiol, ethanethiol, dimethyl sulfide, ethyl methyl sulfide, di-tert-butyl sulfide, thiacyclopentane, thiacyclobutane, 5-thiabicyclo [2.1.1] hexane and 7-thiabicyclo [2.2.1] heptane have been calculated to agree with experimental data, along with the vibrational spectra of the first three of these. The heats of formation of 24 sulfides (including mercaptans) have also been calculated to agree with experimental data. In general, the force field for sulfides seems to be similar in accuracy with that for hydrocarbons.
    Additional Material: 19 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041102
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  • 193
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    Protolytic equilibria of several 4-acyl-substituted 1-phenyl-3-methylpyrazol-5-ones in dioxane-water mixtures (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 667-674 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Thermodynamic proton ionization constants, TpKa, of several 4-acyl-substituted pyrazol-5-ones [acyl = trifluoroacetyl (HPMTFP), acetyl (HPMAP), hexanoyl (HPMHP)] were determined in various dioxane-water mixtures at 25 and 35 ± 0.1°C. The TpKa values were determined by glass-electrode potentiometry and refined by using the extensive weighted least-squares FORTRAN program TPKA. Both extrapolation and leastsquares methods were used to obtain TpKa values in pure water (0%). All three acyl derivatives are weak monoprotic acids with TpKa values between 2.5 and 3.9, following the order HPMTFP 〈 HPMAP ≤ HPMHP. The TpKa values do not vary linearly with the reciprocal of the dielectic constant of the medium; however, a plot of TpKa versus the mole fraction of dioxane, n2, is linear at a given temperature. Values of standard free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes associated with their protolytic equilibria were also calculated. Temperature, medium and substituent effects are briefly discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041104
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  • 194
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    Molecular and electronic structure of substituted bithiophenes (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 675-680 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Several substituted bithiophenes were prepared and their electronic structure studied by photoelectron spectroscopy and semi-empirical MO calculations. Comparison of the spectra of related molecules and analysis of calculated molecular geometries gave an indication of molecular conformations in the gas phase.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041105
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  • 195
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    Structural studies of 1,3-di(N,N-dimethylformamidyl)-2-cyanoguanidine. The case of a strongly lewis basic nitrogen atom in the cyano group VIII. Crystallographic studies of intra- and inter-molecular interactions (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 689-692 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041107
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  • 196
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    Synthesis and NMR study of 5-furylmethylenehydantoins and 5-thienylmethylenehydantoins (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 681-688 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two series of 5-furylmethylenehydantoins and 5-thienylmethylenehydantoins were prepared and their 1H and 13C NMR spectra studied in comparison with those of compounds in the analogous 5-aryl- and 5-pyridyl- series. Differences in the effects of the aromatic, six- or five-membered heteroaromatic rings are discussed. Spectral analysis enables Z/E configurations to be assigned with confidence and conformational preferences to be qualitatively deduced. Some interesting solvent effects were also observed.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041106
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  • 197
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    Masthead (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041201
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  • 198
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    Topological aspects of chemical reactivity. Evans-dewar principle in terms of molecular similarity approach (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 701-705 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Evans-Dewar concept of aromaticity of transition states is given new theoretical support in terms of the similarity approach to chemical reactivity. The principal goal of this approach consists in providing a simple, chemically lucid justification for the legitimacy of the original intuitively formulated concept.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041109
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  • 199
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    Z/E, photoisomerization of 5-arylmethylenehydantoins and 5-pyridylmethylenehydantoins (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 707-713 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Z/E photoisomerization of a series of 5-arylmethylenehydantoins and a series of 5-pyridylmethylenehydantoins by direct irradiation in methanol or ethanol solvent was investigated. The isomeric ratios at the photostationary state are dependent on the excitation wavelength and are related to the relative absorption coefficients of the two isomers. Measurements of quantum yields show the absence of quenching effects by oxygen or azulene, suggesting that triplet states either are not involved or are too short-lived for quenching to be observed. Preparative photoisomerization provides a route to the isomer which is not isolated or obtained only as a minor product by the usual method of synthesis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610041202
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  • 200
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    Reactivity and reaction patterns of alkyl alkoxybenzene radical cations. Mechanistic pathways of the reactions between 2,5-DI-tert-Butyl-1, 4-Dimethoxybenzene and perfluorodiacyl peroxides (1991)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 4 (1991), S. 1-6 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In the reactions of 2,5-di-tert-butyl-1,4-dimethoxybezene (1) with different oxidants, the radical cation 1+. is always detectable by EPR. However, the observed reactivity of 1+. depends greatly on the oxidation systems employed. In S2O82-—Cu2+—HOAc and Ce4+—HOAc systems (HOAc = acetic acid), 1+. appears to have long lifetimes and does not undergo fragmentation spontaneously. In contrast, in (RFCO2)2—CF2CICFCI2 (F113) systems, the readily formed 1+. is short-lived, and large amounts of de-tert-butylation products have been isolated. Experimental results imply that the C—C bond cleavage involved in de-tert-butylation could be a consequence of an attack by perfluoroacyloxy radical on 1+. in their original solvent cage. The fact that addition of methanol to the reaction mixture leads to the formation of a large amount of tBuOCH3 (46%) and other evidence suggest that the tert-butyl group leaves as a carbocation. On the basis of these results, we conclude that the reactions of 1 with (RFCO2)2 are initiated by electron transfer and followed by a fast coupling of various radical species, namely, 1+. with RFCO2 or with RF in the solvent cage, to form σ-complexes which collapse or react with nucleophiles to yield the final products.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610040102
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