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  • 1990-1994  (232)
  • 1990  (232)
  • Physical Chemistry  (232)
  • Nuclear reactions
  • 1
    Electronic Resource
    Electronic Resource
    Rate-equilibrium LFER characterization of transition states: The interpretation of α (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 1-8 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of substituents on the rate of a reaction and the effect of the same substituents on the equilibrium can often be related by a linear free energy relation (LFER): log k- = α log K= + constant, where k+ and K= are the rate constant and the equilibrium constant, respectively. This review, concentrating on group transfers, adds to many studies describing the use of α to describe the transition state. Although the use of α to describe transition states is general, group transfers constitute a simple class allowing a fairly complete description yet illustrating two often neglected contributions. Group transfers can be described by the Marcus equation relating rate to an average identity rate and the equilibrium constant; a major contributor to the slope, α, of the rate-equilibrium LFER is the variation of identity rates with substituent, rather than reflecting product-like character. Substituent effect LFERs are predominantly attributable to interaction of charges with the substituent. However, α is not an exact measure of the charge on the substituent-containing group, because in a transition state, but often not in a reaction product, there are more remote centers of charge which exert a smaller attenuated effect. A simple treatment of this attenuation for group transfers is proposed. The possibility of application of these ideas to proton transfer reactions and the interpretation of the Brønsted α (or β) is proposed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030102
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  • 2
    Electronic Resource
    Electronic Resource
    Solvolysis of highly reactive phosphorus-sulphonic anhydrides. Stereochemical and chemical arguments for phosphathiacylium cation formation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 23-34 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The stereochemistry and mechanism of solvolysis of optically active tert-butylphenylphosphinothioic-O-trifluoromethanesulphonate (1) in solvents of different ionizing power were studied. It was found that in solvents of high ionizing power and low nucleophilicity 1 ionizes with the formation of a phosphathiacylium cation (2) as the reaction intermediate. Product resulting from the reaction of 2 with anisole was isolated and characterized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030106
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  • 3
    Electronic Resource
    Electronic Resource
    Studies on organophosphorus compounds. XXXVI.For Part XXXV, see S. S. Li, Z. Y. Chen and C. Y. Yuan Scientia Sinica (Series B) 136, (1989).. Substituent effects of alkylphosphonates and -phosphinates in alkaline hydrolysis (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 48-54 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Alkaline hydrolysis of diethyl alkylphosphonates and alkyl diethylphosphinates was studied in aqueous dimethyl sulphoxide. The behaviour of these acyclic phosphorus esters is very similar to that of some cyclic phosphorus esters. Rate constants were measured at three temperatures over a 30°C range, and the activation functions of the reaction were estimated. The basic hydrolytic process was proved to be a bimolecular AE reaction. Multiple regression analyses involving rate constants and substituent parameters gave, as a rule, poor results using steric constants derived from carbon compounds. However, the substituent steric effect on the rate of hydrolysis of phosphonates and phosphinates studied correlated very well with ΔΔE, representing the difference in steric energy calculated by molecular mechanics. It is attributed to the various degrees of susceptibility of carbon and phosphorus atoms to the steric hindrance of the substituents. Moreover, Newman's rule of six for the hydrolytic reaction of carboxylates was completely eliminated in phosphorus ester hydrolysis.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030110
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  • 4
    Electronic Resource
    Electronic Resource
    Porphyrin-tyrosine interactions: Photo-CIDNP and NMR studies (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 69-76 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Strong 1H and 13C nuclear polarizations are observed when aqueous solutions of synthetic water-soluble porphyrins are irradiated in the presence of tyrosine and some of its derivatives. These polarizations are strongly pH dependent. Evidence is also shown for the formation, in the dark, of a complex between the reactants. The association constants are evaluated from the NMR chemical shifts on the aromatic tyrosine protons induced by the presence of the porphyrins. The nature of the intermediate radical pair generating the CIDNP effects is discussed. An electron-transfer reaction from tyrosine to the excited triplet state of the porphyrin, or within the porphyrin-tyrosine excited complex, is expected to be the primary step in the reaction. It is followed by subsequent proton transfer within the initial ion radical pair. The spin polarizations arise principally from the back-transfer step, as the reactants are the only products which are polarized.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030202
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  • 5
    Electronic Resource
    Electronic Resource
    The kinetic deuterium isotope effect of proton-transfer reactions in solution. Comparison of the marcus and the quantum-statistical mechanical models (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 62-68 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The free energy dependence of the kinetic deuterium isotope effect of proton-transfer reactions in solution is usually analysed in terms of the Marcus model. By means of modern computer techniques, the more general quantumstatistical mechanical model is also amenable to routine application. The differnces in the basic assumptions of the two approaches concerning the kinetic isotope effect are discussed. Reaction series for which both the Brønsted relation and the free-energy dependence of the kinetic isotope effect are available are analysed by means of the two models using one set of parameters for both free-energy relations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030112
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  • 6
    Electronic Resource
    Electronic Resource
    Brønsted coefficients and the theory of acid-base catalysis of proton transfers from carbon acids (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 95-109 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intersecting-state model previously used to interpret proton transfers in ground and excited states and enzyme catalysis was applied to the general acid-base catalysis of carbon acids. The results are consistent with the predictions published for these systems and provide a new physical meaning for the Brønsted coefficients. It is shown that in addition to the linear free energy effect, the Brønsted coefficients are also influenced by the tightness of the transition states and by electronic effects. The model suggests that the increased reactivity of carbon acids towards proton transfer in non-hydrogen-bonding solvents is caused by an added electronic effect on the thermodynamics of the reactions. The curvatures of the Brønsted plots are interpreted in terms of an entropic contribution to the position of the transition state.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030206
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  • 7
    Electronic Resource
    Electronic Resource
    Topological evidence for an N—N bond in cis-1,2-dinitrosoethene: The remarkable structure of the di-N-oxide of 1,2-diazacyclobutadiene (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 143-146 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Analysis of the topological properties of the electron density distribution of cis-1,2-dinitrosoethene (I) shows that there is a normal covalent, albeit very long, single bond between the nitrogen atoms in the molecule, which is in fact the di-N-oxide of 1,2-diazacyclobutadiene (II). Despite its extraordinary length, the N—N bond is shown to be consistent with the strong correlation between the electron density at the bond critical points and the calculated bond lengths of N—N bonds. The geometry and electronic structure exhibit a number of remarkable features.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030303
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  • 8
    Electronic Resource
    Electronic Resource
    Deuterium fractionation factors for carbon-hydrogen bonds: Calculations using scaled quantum-mechanical force constants (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 181-189 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The determination of uniform scaling factors for force constants calculated at the STO-3G and 4-31G levels of ab initio SCF MO theory is described; scaled 4-31G force constants provide reasonable estimates of reduced partition function ratios for deuteriated/protiated molecules. Gas-phase deuterium fractionation factors relative to methane calculated using scaled 4-31G force constants are, however, consistently too high, whereas those obtained by the MP2/6-31G* and scaled STO-3G methods are inconsistent. Scaled 4-31G deuterium fractionation factors relative to water for a range of structural moieties correlate linearly with experimental aqueous-phase values, but are also consistently overestimated. Substitution at a hydrogen-bearing carbon atom affects the deuterium fractionation factor through the combined effect of changes in reduced mass and changes in force constants other than for CH stretching.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030307
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  • 9
    Electronic Resource
    Electronic Resource
    Kinetics and mechanism of the oxidation of organic sulphides by N-chloroacetamide (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 174-180 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the oxidation of a number of monosubstituted aryl methyl, alkyl phenyl, dialkyl and diphenyl sulphides by N-chloroacetamide (NCA) to yield the corresponding sulphoxides were studied. The reaction is first order with respect to the sulphide, NCA and hydrogen ions. There is no effect of added acetamide. Protonated NCA has been postulated as the reactive oxidizing species. The rates of oxidation of meta- and para-substituted phenyl methyl sulphides were correlated with Taft's and Swain's dual substituent parameter equations. For the para-substituted compounds, the best correlation is obtained with σI and σR+; the meta-substituted compounds correlate best with σI and σR° values. The reaction constants are negative. The oxidation rates of the ortho-substituted sulphides yield an excellent correlation in a triparametric equation involving Taft's σI and σR+ values and Charton's steric parameter, V. The oxidation of alkyl phenyl sulphides is susceptible to both polar and steric effects of the alkyl group. A mechanism involving the formation of a halogenosulphonium cation in the rate-determining step is proposed.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030306
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  • 10
    Electronic Resource
    Electronic Resource
    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610030401
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  • 11
    Electronic Resource
    Electronic Resource
    15N NMR of nitranions: Opposite shift effects of σ and π charge (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 139-142 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nitranions of pyrrole, aromatic and heteroaromatic amines, carboxamides and pyridyl carbanions are generated by deprotonation either of NH or CH acids. The positive or negative displacements undergone by the 15N nucleus relative to the neutral precursor depend on whether a σ or π charge is increased. They are associated with the symmetry of the nitrogen orbital in which the electron pair is either generated or that to which it is delocalized.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030302
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  • 12
    Electronic Resource
    Electronic Resource
    AM1 calculations on the tautomerism of free and hydrated hydroxypyridines: Barriers to proton transfer in 2-hydroxypyridine-pyrid-2(1H)-one and effect of solvation and self-association (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 332-338 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: AM1 calculations for the tautomerism of the three isomeric hydroxypyridines are reported and compared with recent ab initio results. Intrinsic stabilities of the various tautomers are predicted by AM1 with an accuracy comparable to or even better than the best available ab initio calculations. Solvation is accounted for by the supermolecule approach and also a continuum model for solvent effects. Except for 3-hydroxypyridine, AM1 correctly accounts for the observed shift of the tautomeric equilibria due to hydration. Energetics of hydrogen bonding are reasonably described by this semiempirical method. With respect to structures, bifurcated hydrogen bonds are preferred by AM1. In addition, for 2-hydroxypyridine and its lactam tautomer self-association in addition to barriers to proton transfer are considered. With respect to tautomerization transition states, AM1 shows serious shortcomings. Compared with both experimental and ab initio results, barriers to proton transfer are considerably overestimated by AM1, especially in the hydrated and associated species. For the dimers AM1 predicts an unsymmetrical transition state which, however, is only slightly lower in energy than the symmetrical structure with two negative eigenvalues of the force constant matrix. Despite several attempts, the transition state for proton transfer in the doubly hydrated species could not be located.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030510
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  • 13
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    Electronic Resource
    Structural studies of halogen adducts of diorganyl chalcogenides in solutions by 1H, 13C, 77Se and 125Te NMRFor a preliminary contribution, see Ref. 1. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 358-368 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1H, 13C, 77Se and 125Te NMR spectra were measured for several sulphides, selenides, tellurides and their halogen adducts to establish the criteria for distinguishing trigonal bipyramidal (TB) adducts from molecular complexes (MCs). TB formation caused large downfield shifts for methyl protons and methyl, ipso and para carbons of methyl and phenyl selenides and tellurides. Large downfield shifts (〉 100 ppm) were also observed for selenium and tellurium by the formation of TB from the parent selenides or tellurides. The plots of the 125Te vs 77Se chemical shifts for a set of corresponding compounds gave a straight line with a slope of 1·74, showing that the linear relationship holds well for tellurides and selenides and their TB adducts examined in this work. Upfield shifts of the ipso carbons were characteristic of MC formation. The para carbon signals of MC appeared downfield relative to those of the parent selenides, although the shift values were not so large. The 77Se signals for MC shifted slightly downfield (≤ 10 ppm). The dissociation constants for iodine adducts of dimethyl selenide and selenoanisole were determined. The MC structure of bromine adducts of sulphides is well demonstrated on the basis of the criteria set out. 1H and 13C NMR spectra of ethylbenzene and ethers were also recorded in the presence of iodine or bromine. However, their chemical shifts were the same as those in the absence of iodine or bromine, within experimental errors.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030603
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  • 14
    Electronic Resource
    Electronic Resource
    Concentration-dependent deuterium isotope effects on the quantum yield of arene-alkene meta photocycloaddition: The role of excimers (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 273-278 
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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 deuterium isotope effect on the arene-alkene meta photocycloaddition, reported earlier for toluene/toluene-d8 photoaddition to cyclopentene, was found to depend on the concentration of both arene and alkene. This phenomenon is explained in terms of an unbalanced dissociation of ‘mixed’ excimers, which play a role in the intermolecular competition experiments.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030411
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  • 15
    Electronic Resource
    Electronic Resource
    Kinetics and mechanism of acid hydrolysis of 2-carboethoxypyridine N-oxides (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 489-492 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Rate constants and activation parameters have been measured for the acid hydrolysis of six 2-carboethoxypyridine N-oxides. The correlations of log kobs. vs Hammett's constants and chemical shifts of intramolecular hydrogen-bonded protons in parent acids are analysed. Evidence was found for the participation of intramolecular hydrogen bonding in the hydrolysis of the esters.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030802
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  • 16
    Electronic Resource
    Electronic Resource
    Solvent polarity scales. 1. Determination of ET and π* values for phosphonium and ammonium melts (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 534-544 
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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 solvent polarity of a series of organic salts in their molten state has been determined using the solvatochromic dyes: pyridinium N-phenolate betaine, the basis of the ET scale, and N,N-diethyl-4-nitroniline, one of the primary standards for the π* scale. Each of these dyes was dissolved in the following liquids: lithium acetate-sodium acetate-potassium acetate eutectic; ethylammonium chloride; dimethylammonium cloride; diethylammonium nitrate; ammonium trifluoracetate; tetraethylammonium acetate; tetrabutylphosphonium chloride; octyltributylphosphonium chloride; dodecyltributylphosphonium chloride; tetrabutylammonium bromide; tetrabutylphosphonium bromide; octyltributylphosphonium bromide; dodecyltributylphosphonium bromide; octyltributylphosphonium iodide; dodecyltributylphosphonium iodide; tetrahexylammonium benzoate; methyltrioctylphosphonium dimethylphosphate; and methyltrioctylammonium chloride. The ultraviolet and visible spectra were measured for each of these. In addition, data were collected as a function of temperature and in the presence of neutral and ionic additives. In general, these molten salts represent solvent polarities equivalent to moderately polar aprotic solvents such as acetone and acetonitrile. The salts with cations capable of being hydrogen bond donors gave considerably higher values, equivalent to or higher than water, the solvent with the highest value on the ET scale. These and the eutectic mixture are thought to involve specific dye-solvent interactions which cause these anomalously high values.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030807
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  • 17
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    Electronic Resource
    Ion association and reactivity of the alkali metal salts of alkanoic acids in dipolar aprotic solvents (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 428-434 
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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 effect of added alkali metal perchlorates on the rate of lactonization of ω-bromoalkanoate ions was investigated in 99% dimethyl sulphoxide (four-membered ring formation) and in dimethylformamide (DMF) (four- and sixteen-membered ring formation). In all cases the effect of the added metal salts is rate depressing, as a result of the lower reactivity of metal ion-associated species relative to the free ions. Ion-pairing association constants were determined, but the reactivity of ion pairs were so low as to elude direct measurement in most cases. Evidence was also obtained for the formation of ion triplets with Li+ in DMF. The relevance of the present results in connection with the ‘caesium effect’ is briefly discussed.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030703
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  • 18
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    Electronic Resource
    Electronic factors in the elimination kinetics of 2-halosubstituted methanesulphonates in the gas phaseTaken from the thesis of Jaime Alvarez G., submitted to the Faculty of IVIC, 1989, in partial fulfillment of the requirements for the Degree of Magister Scientiarum. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 456-458 
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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 kinetics of the gas-phase elimination of two 2-haloethyl methanesulphonates were determined in a static system over the temperature range 310-380°C and pressure range 26-174 Torr. The reactions in seasoned vessels, with the free-radical inhibitor propene and/or toluene always present, are homogeneous and unimolecular, and follow a first-order rate law. The rate coefficients are given by the Arrhenius equations: for 2-bromoethyl methanesulphonate log k1 (s-1) = (11·70 ± 0·43)-(172·8 ± 4·8) kJ mol-1 (2·303RT)-1 and for 2-chloroethyl methanesulphonate log k1 (s-1) = (11·67 ± 0·50)-(173·9 ± 6·0) kJ mol-1 (2·303RT)-1. The bromo compound was found to be more reactive than the chloro compound. At 340°C, for Br k1 = 9·46 × 10-4 s-1 and for Cl k1 = 7·12 × 10-4 s-1. Apparently, electronic factors seem to be operating in these elimination reactions.
    Additional Material: 3 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030707
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  • 19
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    Electronic Resource
    Substituent effects in the solvolysis of benzyl tosylates (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 449-455 
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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 substituent effect on the rates of solvolysis of substituted benzyl tosylates in acetic acid was analysed based on the Yukawa-Tsuno LArSR equation. Neither the LArSR nor simple σ+ treatment was capable of providing any linear correlation plot for the full range of substituents. The σ+ plot was not simply bilinear but widely scattered, giving a split pattern of parallel curves with significant gaps. Since any mechanistic transition with substituents should bring about a single continuous curve when plotted against an appropriate substituent constant scale, the split σ+ plot is not in line with an interpretation in terms of a mechanistic transition. On the other hand, the LArSR plots with r = 1·3 coalesced into a single smooth curye including the meta correlation curve. A different resonance demand as high as r = 1·3 is required in order to give a smooth single-curve correlation for the entire substituent range without splitting. For the reactive substituents down to p-halogens, a sufficiently linear plot can be obtained against a set of substituent constants with r = 1·3 which can be referred to the substituent effect correlation for the kc mechanism of this system. An identical r value was likewise assigned for the kc mechanism of the hydrolysis for a more severely restricted range of activating substituents down to the 4-MeS-3-CN group.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030706
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  • 20
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    Electronic Resource
    Effects of CF2 group pyramidalization in the 1,1,3,3-tetrafluoropropenyl anion (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 635-638 
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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: Ab initio calculations with the 6-31G* basis set were carried out on planar and pyramidalized geometries of the 1,1,3,3-tetrafluoropropenyl anion and on two geometries with one CF2 group rotated out of conjugation. Structures with at least one pyramidalized CF2 group are substantially lower in energy than the corresponding unpyramidalized structures for both rotated and unrotated geometries. At the MP2/6-31G* level of theory, three structures of approximately equal energy all lie 17-18 kcal mol-1 below the planar C2v structure. These include a Cs geometry with one CF2 group rotated out of conjugation, an unrotated C1 structure with unequal CC bond lengths and an unrotated, pyramidalized C2 structure with equal CC bond lengths.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031003
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  • 21
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    Electronic Resource
    Rearrangement and cyclization in the ionization of the 4-chloro-3-methylbutanoyl cation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 639-642 
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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 second ionization of the 4-chloro-3-methylbutanoyl ion forms a primary alkyl acyl dication, as a tight ion pair. Methyl and hydrogen shifts occur to comparable extents indicating that the relative stability of the product (sec- or tert-carbocation) does not influence the energy barrier for the shift. The product of methyl shift (1,3-sec-alkyl acyl dication) loses the proton closest to the counterion in the tight ion pair and forms the pent-3-enoyl cation. Protonation-deprotonation of the latter, followed by internal acylation, gives the protonated cyclopent-2-enone. The dication resulting from hydrogen shift loses a proton from C-2 and gives the 3-methylbut-2-enoyl cation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610031004
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    Synthesis and chemistry of azolenines.The term ‘azolenines’ refers to the non-aromatic isomers of the azoles. Part 19.For Part 18, see Ref. 1. Basicities of some 2H- and 3H-pyrroles and the remarkably large pKa′ of 2,2,3,5-tetramethyl-2H-pyrrole (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 555-557 
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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: pKa′ Values are reported for two 2H-pyrroles and their 3H-pyrrole isomers. The latter have basicities of the same order as similarly substituted pyridines, whereas the former are 2-2·5 pK units more basic, 2,2,3,5-tetramethyl-2H-pyrrole having a pKa′ of 8·40, close to that for 2-aminoimidazole. Possible reasons are given.
    Additional Material: 1 Tab.
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  • 23
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    Activation barriers in photosensitized pyrimidine dimer splitting (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 581-586 
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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: Pyrimidine dimers, which form by a symmetry allowed (πs2 + πs2) photocycloaddition reaction, are subject to photosensitized cycloreversion by electron donors, such as indoles. In a linked dimer-indole system, photoinitiated electron transfer occurs intramolecularly from indole to dimer to produce a charge-separated species (dimer-.-indole+.). This species undergoes cycloreversion in competition with back electron transfer. Studies of the temperature dependence and solvent dependence of this competition have allowed the relative values of the activation parameters for the competing processes to be determined. In water (5-65°C) the free energy of activation of splitting minus that of back electron transfer (ΔΔG≠ = ΔGspl≠ - ΔGbet≠) was found to be 1·3 kcal mol-1. The enthalpy of activation difference (ΔΔH≠) was found to be 1·1 kcal mol-1 and the entropy of activation difference (ΔΔS≠) was found to be -0·51 cal mol-1 K-1. In EPA (diethyl ether-isopentane-ethanol, 5:5:2; -85 to 25°C) the value of ΔΔG≠ remained the same, but the entropy and enthalpy contributions were different (ΔΔH≠ = 0·72 kcal mol-1; ΔΔS≠ = -1·8 cal mol-1 K-1). The results have been interpreted in terms of the effect of the polarity of the solvent on the transition states for the two competing processes. Enthalpy effects retard splitting more in water than in EPA, whereas entropy effects favor back electron transfer more in EPA than in water. Potential implications of these results for the mechanism of enzymatic photocycloreversion of pyrimidine dimers in DNA are considered.
    Additional Material: 3 Ill.
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  • 24
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    Borohydride reduction of alkyl phenyl ketones within a reversed-phase liquid chomatographic column (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 594-598 
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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 reductions of propiophenone and octanophenone to 1-phenylpropan-1-ol and 1-phenyloctan-1-ol, respectively, with sodium borohydride and tetrabutylammonium borohydride were performed on a reverse-phase highperformance liquid chromatographic (HPLC) column of macroporous 10-μm poly(styrene-divinylbenzene) undr HLPC conditions. In these reactions a lower concentration of tetrabutylammonium borohydride than of sodium borohydride was needed to effect the same extent of reduction, and modest substrate selectivity was obtained.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030907
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  • 25
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    Benzyloxyfluorocarbene: Resistance to fragmentation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 694-696 
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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: Benzyloxyfluorocarbene resists fragmentation to benzyl fluoride, and can be intercepted by water, fluoride ion, methanol or acrylonitrile. In contrast, benzyloxybromocarbene and benzyloxychlorocarbene fragment to the corresponding benzyl halides, and are not efficiently trapped.
    Additional Material: 1 Tab.
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  • 26
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    The current status of isomer enumeration of useful benzenoids and a new topological paradigm (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 765-783 
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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 enumeration and development of conceptual tools for understanding the chemical properties of practical benzenoid hydrocarbons is stressed. Currently known isomer numbers for benzenoids having up to 60 carbons are summarized. Although there are well over 2 million isomers in this range, only approximately 500 benzenoid hydrocarbons have been characterized.
    Additional Material: 8 Ill.
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  • 27
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    Absolute hardness and aromaticity: MNDO study of benzenoid hydrocarbons (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 784-788 
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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: Absolute hardness calculated by the MNDO method has been shown to be a good measure of aromaticity for 14 benzenoid hydrocarbons. Comparisons among hardnesses at different levels of approximation are given. The parallelism of the aromaticity and hardness concepts in benzenoids is elaborated.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031203
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  • 28
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    Kinetics of oxidation of amino acids by alkaline hexacyanoferrate(III) (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 799-802 
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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 kinetics of the oxidation of α-amino acids (glutamic acid and aspartic acid) by alkaline hexacyanoferrate(III) were studied at constant ionic strength and over the temperature range 323-348 K. The rate was dependent on the first power of the concentrations of substrate and oxidant, but was independent of the concentration of alkali in the range studied. The value of kH/kD was in the range 8·1-8·3 for the slow step, indicating the loss of a hydrogen atom from the C—H bond, giving a radical species which was characterized by ESR spectroscopy. The reaction proceeds by way of the α-imino acid, formed in a fast step, which undergoes hydrolysis to give the corresponding α-keto acid.
    Additional Material: 1 Ill.
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  • 29
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    Mechanisms of acylation of 2,3-dihydrobenzoxazol-2-one and 2H-1,4-benzoxazin-3(4H)-one (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 807-811 
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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 kinetics of the acylation of 2,3-dihydrobenzoxazol-2-one with dodecanoic acid in polyphosphoric acid were investigated. Two competitive reactions occurred at the 3- and 6-positions. The acylation reactions in polyphosphoric acid of 2,3-dihydrobenzoxazol-2-one and 2H-1,4-benzoxazin-3(4H)-one give 6- and 7-acyl derivatives. 4-Acetyl-2H-1,4-benzoxazin-3(4H)-one rearranged in polyphosphoric acid exclusively to the 7-acetyl derivative. Two mechanisms are proposed to explain the different reaction sites for the acylation of 2H-1,4-benzoxazin-3(4H)-one.
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  • 30
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    Stereospecificity in anionic 1, 1-addition to isocyanides. A re-examination of the (H- + HN≡C) potential energy surface (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 697-702 
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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 potential energy surface for the addition of the hydride ion to hydrogen isocynide reported previously was re-examined. An improved energy surface was explored at the MP2/6-31 + + G** level while relative energies were estimated at the MP4SDTQ/6-311 + + G** level and corrected for zero-point vibrational contributions. The calculated results show the existence of transition structures for both cis and trans-additions of H- to the carbon end of HN≡C even though the corresponding barrier heights are small. These transition structures did not exist at a lower level of theory (HF/4-31G) employed previously.The cis addition is calculated to be favoured over the trans addition by 10 kcal mol-1. The overall addition is thus strongly stereoselective, if not purely stereospecific. This result confirms our previous analysis of the stereoelectronic effect in the addition-elimination process involving imidoyl anions as intermediates. Recent experimental work on the addition of OH- to ArN≡C is discussed.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031102
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  • 31
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    Comparison between some semi-empirical and ab initio Hartree-Fock models for the description of amides (formamide revisited) (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 711-722 
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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 comparative study on the use of the MINDO/3, MNDO and AM1 semi-empirical methods for the description of formamide and aliphatic amide systems is reported. For formamide, ab initio Hartree-Fock calculations are also reported using both the STO-3G and 3-21G basis sets, as well as a basis set obtained by a minimal relaxation of the STO-3G contraction scheme. It is shown that both the MNDO and the STO-3G methods cannot properly reproduce the experimental results. In both cases this appears to be due to inadequacies of the basis sets used. Again in both cases only small improvements in the basis set necessary to allow for the diffuse character of the pπ orbitals lead to dramatic improvements in the calculated results. In the case of the STO-3G basis set this is demonstrated by the fact that a small relaxation in the contraction leads to results even superior to those with the 3-21G set. The conclusions reached for amide systems can be extended to other systems where planarity around or inversion with respect to nitrogen is an issue. This is demonstrated for ammonia.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031104
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  • 32
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    Mechanism of formation of phosphonate carbanions with the use of a lithium salt and 1,8-diazabicyclo[5.4.0] undec-7-ene (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 746-750 
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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 deprotonation reaction mechanism of methyl diethylphosphonoacetate in the presence of lithium salts and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was examined by infrared spectroscopy. It was found that the intermediate species formed by chelation of the bidentate phosphonate with a lithium cation or an ion pair of the salt deaggregated by DBU takes part in the reaction path. The role of the anion X- is to induce the elimination of a protonated DBUH+X- ion pair and that of the solvent is to compete with the bidentate phosphonate in cation solvation. A similar mechanism via a related intermediate is proposed to interpret the results obtained by other workers on the catalysis by Ba(OH)2 of the Wittig-Horner reaction.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031108
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    Negligible kinetic solvent interactions for the rate of photobromination of toluenes where the bromine atom is a principal chain carrierDedicated to Professor Ikchoon Lee on the occasion of his 60th birthday. Preliminary results of this work have been presented earlier. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 803-806 
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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 bromine atom is a major chain carrier in the photobromination of toluenes by N-bromosuccinimide. Only an uncomplexed bromine atom can abstract hydrogen atoms from toluenes. The nature of the polar transition state is entirely different from that of solvolytic reactions and the solvent polarity therefore cannot infuence the rates of the bromination.
    Additional Material: 1 Tab.
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610030101
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  • 35
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    Quantification of resonance in thioamides from infrared spectral data (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 13-16 
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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 model is proposed for the quantification of resonance in thioamides. The percentage resonance and CS and CN bond distances predicted from the model are reported and the results are compared with those for the corresponding amides.
    Additional Material: 1 Ill.
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  • 36
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    Probing of transient photoenol formation from ortho-methyl-substituted phenyl ketones by hydrogen-tritium exchange (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 38-40 
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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: Studies on the photochemically induced hydrogen-tritium exchange in o-methyl-substituted phenyl ketones are reported. It is shown that the tritium exchange can be beneficial for probing transient photoenol formation, particularly when photochemical side-reactions are occurring.
    Additional Material: 1 Tab.
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  • 37
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    Rates of hydrogen exchange and kinetic isotope effects in the reaction of p-nitrophenylnitromethane with amine bases in toluene solution: Absence of internal return (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 55-61 
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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: Rates of loss of tritium from p-nitrophenylnitromethane-α-t in toluene solution catalyzed by a series of amine bases show that hydrogen exchange in this system occurs at the same rate as ionization of the carbon acid, and that internal return is not taking place. This substantiates a previous suggestion that very large deuterium isotope effects reported for some of these reactions and attributed to extensive tunnelling were determined under conditions where the isotopic label was being lost and are therefore artifacts. This study provides isotope effects which are generally much smaller than those reported previously, but some tunnelling may still be taking place in some of these reactions.
    Additional Material: 4 Ill.
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  • 38
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610030201
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  • 39
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    Maximally inhibited elimination of kinetics of (2-bromoethyl)benzene and 1-bromo-3-phenylpropane in the gas phase. Anchimeric assistance of the phenyl group (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 77-80 
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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 gas-phase elimination kinetics of (2-bromoethyl)benzene and 1-bromo-3-phenylpropane were studied in a static system and seasoned vessels over the temperature range 390-450 °C and the pressure range 32-104 Torr. The reactions, under maximum inhibition of 4-fold pressure of the free-radical suppressor cyclohexene and/or propene, are homogeneous, unimolecular and obey a first-order rate law. The rate coefficients are given by the following Arrhenius equations: for (2-bromoethyl)benzene, log k1 (s-1) = (13·04 ± 0·10) - (210·8 ± 1·3) kJ mol-1 (2·303RT)-1, and for 1-bromo-3-phenylpropane, log k1 (s-1) = (14·09 ± 0·27) - (227·7 ± 3·6) kJ mol-1 (2·303RT)-1. The phenyl group of (2-bromoethyl)benzene appears to provide anchimeric assistance in the HBr elimination of this compound. However, neighbouring C6H5 participation at the 3-position in 1-bromo-3-phenylpropane for a C-4 conformation is apparently absent. The mechanisms of these reactions are discussed.
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    MNDOC-CI calculations for organic photoreactions. I. The α-cleavage reaction of carbonyl compounds (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 81-88 
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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: MNDOC-CI results are reported for the photochemical α-cleavage reaction of carbonyl compounds. Potential energy surfaces for some excited singlet and triplet states and cross-sections along the bitopic reaction path show that the activation energy of the α-cleavage reaction is determined by the relative energetic position of the lowest two triplet states. The reactivity of aliphatic ketones depends only on the degree of branching at the α-carbon, because the triplet barrier is due to an (avoided) crossing of two surfaces corresponding to an nπ* and ππ* excitation respectively, which correlates with the stability of the leaving alkyl radical. For conjugated carbonyl compounds, on the other hand, the position of the crossing point is independent of the 3nπ* excitation energy, but if the 3ππ* surface is below the 3nπ* surface all the way along the reaction coordinate, the reaction is determined by the barrier on the 3ππ* surface and any additional stabilization of the 3ππ* state increases the barrier.
    Additional Material: 6 Ill.
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  • 41
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    Stereochemical studies. XXXIVPart XXXIII, I. G. Mursakulov, V. A. Svyatkin, V. V. Samoshin, N. S. Zefirov, Zh. Org. Khim. 22, 773-776 (1986).. Quantitative description of ring puckering via torsional angles. The case of six-membered rings (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 147-158 
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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 quantitative description of ring puckering suggested by the authors is compared with that of Cremer and Pople. The applicability of both methods is discussed for the case of six-membered rings with the use of model calculations simulating various ring distortions and with the analysis and comparison of puckering parameters computed on the basis of x-ray data for 40 six-membered rings in different cyclic structures. The 2N times reduction of the field of variation of puckering parameters for the N-membered ring is suggested and the algorithm for the renumbering of the ring atoms for this purpose is described for six-membered rings.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030304
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  • 42
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    Electron distribution in the molecule of nitronesPart XII in the series Oxime Derivatives, simultaneously Part XI in the series Mesomeric Dipole Moments. For Preceding parts, see Refs 11 and 49. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 190-194 
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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: Vector analysis of dipole moments of two series of nitrones revealed a mesomeric dipole moment compatible with a relatively great contribution of a zwitterionic structure and possible some contribution from a hypervalent structure. The latter was also suggested from a detailed comparison of bond lengths among several classes of compounds, involving the CNO grouping. Since both the C=N and N—O bonds seem to possess an appreciable double bond character, it is suggested that the N atom might be allocated more then eight valence electrons.
    Additional Material: 2 Ill.
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  • 43
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    Photochemistry of pyridinium salts 1. Intramolecular charge transfer in N-amino-substituted pyridinium cations (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 200-204 
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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 photophysics and photochemistry of N-amino-substituted pyridinium salts were investigated. Electron transfer from the amino group to the pyridinium ring takes place in the singlet excited state. The fluorescence quenching and photoreactivity of these compounds is conditioned by this process. Irradiation of N-aminopyridinium salts in solution leads to novel fused heterocycles or to triphenylpyridine, depending on the concentration of the initial compound. Free radical intermediates are involved in the photoreaction.
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    Triple ion chelate structure of an equilibrium Michael adduct (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 205-208 
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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 equilibrium adduct from the Michael reaction between lithium dimethylphenylacetamide enolate and methyl cinnamate has been studied by means of 7Li, 13C and 1H NMR and IR spectroscopy as well as by electrical conductivity measurements in THF and diethyl ether. The 7Li NMR and the electrical conductivity measurements data are consistent with a triple ion structure of [A-M+A-]- M+ type, favoured in THF. All other spectral data support an intramolecular chelation in the triplet fragment.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030311
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    Relationship between substituent electronegativity and field parameter in the aliphatic series. Introduction of charge separation parameter (λ) (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 209-218 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The problem of non-proportionality between the substituent field parameter (σF) and substituent electronegativity (Δι or σχ) was clarified by the introduction of the ‘charge-separation parameter’ (λ), which is the component for the direction of the H—X axis of the distance between positive and negative poles of the dipole in the H—X molecule. Thus σF was correlated with Δι or σχ by the equation σF = aΔιλ (or σF = a′σχλ). The above proposal was further supported by performing an energy decomposition analysis for the isodesmic reaction in the isolated molecule system (\documentclass{article}\pagestyle{empty}\begin{document}${\rm X}\raise1pt\hbox{---} {\rm H} \cdots {\rm H}\mathop {\rm N}\limits^ + {\rm H}_3 $\end{document} or X—H…HCO2-) at shorter distances (2·0-4·5 Å). It was further shown that field parameters such as σi, F and σF(theor), and the pKa values in the series of aliphatic acids, and spectral data (UPS and 13C-SCS) were also well correlated with Διλ or σχλ. It is concluded that λ and Δι or σχ are essential parameters for interpreting the electrostatic field effect in aliphatic substituent effects, and that the transmission due to the σ-inductive effect is considered to be not as significant as the field effect after a few bonds away from the substituent.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030402
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  • 46
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    Contrasting kinetic behaviour of allyl and crotyl alcohols towards N-bromosuccinimide in aqueous methanol (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 235-238 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactions of N-bromosuccinimide (NBS) with allyl and crotyl alcohols in aqueous methanol are first order in NBS. Allyl alcohol displays a zero-order dependence whereas crotyl alcohol exhibits a Michaelis-Menten-type dependence on substrate concentration. The NBS-allyl alcohol reaction is inhibited by H+ whereas the NBS-crotyl alcohol reaction is independent of [H+]. However, both are fast in the absence of acid. The rates are unaffected by the addition of neutral salt and succinimide. The reaction of NBS with crotyl alcohol exhibits a positive dielectric effect whereas allyl alcohol displays no such effect. Inhibition by HgII is observed in the crotyl alcohol reaction but not with allyl alcohol. 3-Bromo-2-methoxypropan-1-ol is the product of the allyl alcohol reaction but a mixture of 2-bromo-3-methoxybutan-1-ol and 2-bromobutane-1,3-diol in the crotyl alcohol reaction. In the allyl alcohol reaction the formation of solvated bromonium ion and of HOBr is suggested as rate-limiting steps. In the crotyl alcohol reaction, rate determining breakdown of an NBS-crotyl alcohol complex, formed in a fast pre-equilibrium, is proposed.
    Additional Material: 5 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030405
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  • 47
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    Lone-pair charges and structural effects (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 255-259 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The lone-pair charge, Qlpf, of a base B is a (theoretically calculated) measure of the amount of charge on the lone pair of B that binds to an acid Av (v = 0, 1) in an acid-base reaction. It is shown how they can be used for the quantitative study of structural effects on gas-phase proton affinities, vertical ionization potentials and hydrogen-bonding basicities.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030408
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  • 48
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    syn-anti Isomerism in the 1,3-dipolar cycloaddition to cis-3,4-disubstituted cyclobutenes. 4. Intramolecular interactions (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 159-173 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ab initio (4-31G) molecular geometry optimizations on cis-3,4-disubstituted cyclobutenes show that the extent and direction of their ground-state pyramidalization depend on the type of substituents and on whether these substituents are part of a ring condensed on to the cyclobutene moiety. Thus, electron-withdrawing substituents such as Cl and OMe bring about an out-of-plane anti bending of the olefinic hydrogens, whereas cyclobutenes condensed on to small carbocyclic rings exhib high syn bending. Intramolecular interactions are analysed in the frame of a new model where the interactions arise from the energy matrix elements between the hybrid atomic orbitals involved in the different bonds. The analysis is carried out by C-INDO calculations on deformed molecules (with the olefinic hydrogens forced out-of-plane by ± 20°). These latter calculations reveal that non-planarity of the double bond occurs in the direction of increasing interactions between the hybrid atomic orbitals involved in the σ-allylic bonds and in the π-bond. The increase in this kind of interaction can also explain non-planarity in norbornene, 7-oxanorbornene, 5,6-dioxanorbornene and 5,6-dioxabicyclo [2.2.2] oct-2-ene. The results strongly suggest that pyramidalization and the related energy asymmetry of out-of-plane bending of olefinic hydrogens are important factors in governing facial selectivity of 1,3-dipolar cycloadditions to cis-3,4-disubstituted cyclobutenes.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030305
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  • 49
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    The decay of 2-phenyl-1,3-dioxolane-2-ylium salts in solution (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 195-199 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The decay of 2-phenyl-1,3-dioxolane-2-ylium salts in 1,2-dichloroethane solution has been studied by means of 1H NMR and UV spectroscopy and conductimetry. The influence of the nature of the anion (SbCl6-, SbCl5Br-, AsF6-) and of the methyl substituents on the rate constants of decay is discussed.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030309
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  • 50
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    Stern-Volmer quenching kinetics in photoreaction systems with strong internal filtering: Type II photoreaction of 2-benzoylcyclohexanone (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 230-234 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Stern-Volmer quenching equation for a photochemical reaction in the presence of internal filtering was obtained by applying the steady-state approximation to the system. The equation was used for the kinetic analysis of the Type II photoreaction of 2-benzoylcyclohexanone yielding 1-phenylhept-6-ene-1,3-dione, the enol form of which acts as an effective internal filter. The kqτ value for quenching of the photoreaction by 2,5-dimethylhexa-2,4-diene was determined to be 9·1 ± 0·5 l mol-1.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030404
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    Photochemical electrocyclization of the allyl radical into the cyclopropyl radical (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 219-229 
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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: Following the observation that allyl radicals trapped in an argon matrix can be photolytically converted into cyclopropyl radicals (λ = 410 nm, 18 K), the IR spectrum of the cyclopropyl radical was recorded for the first time and interpreted. Bicyclopropane and cyclopropane are formed when the photolysed argon matrix is warmed from 18 to 35 K. The identification of these new species unequivocally proves the presence of cyclopropyl radicals in the photolysed matrix. This radical is shown to be a σ-type (Cs symmetry) and not a π-type (C2v symmetry) radical; of the 18 normal frequencies of the Cs cyclopropyl radical, all active in the IR, 16 were observed and were assigned to their corresponding normal modes. For this assignment advantage was taken of ab initio frequency computations reported in the literature and performed by the authors.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030403
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    A study of a novel degenerate carbocation rearrangement of the 4,9-dimethyl-9-barbaralyl cation by dynamic 13C and 1H NMR spectroscopy in superacid (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 349-357 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 4,9-dimethyltricyclo [3.3.1.02,8]nona-3,6-dien-9-yl (4,9-dimethyl-9-barbaralyl) cation (3) was generated from 4,9-dimethyl-9-barbaralol (5) at -135°C in two different superacid mixtures [FSO3H—SO2CIF—SO2F2(1:6:1) and FSO3H—SO2CIF—SO2F2—CHCl2 (2:10:10:1 by volume)]. Its 1H and 13CNMR spectra show a strong temperature dependence in the range -150 to -125°C. The changes in band shapes with temperature show that the following exchanges take place: 4-methyl with 9-methyl, C-4 with C-9, C-1 with C-3 and C-2 with C-8. C-5, C-6 and C-7 are found not to exchange rapidly either with each other or with the other carbons in 3. The mechanism of this novel rearrangement is suggested to involve the bicyclic 2,7-dimethylbicyclo [3.2.2] nona-3,6,8-trienyl cation and the secondary barbaralyl cation 4,6-dimethyltricyclo [3.3.1.02,8] nona-3,6-dien-9-yl as intermediates rather than 7,8-dimethyl bicyclo [3.2.2] nona-3,6,8-trienyl cation, which does not have a methyl group on the allyl cation moiety. Comparisons with rearrangement mechanisms for other barbaralyl cations were also made. The rate constant for the degenerate rearrangement of 3 is 160 s-1 at -140°C, which corresponds to ΔG≠s = 26 kJ mol-1 (6·3 kcal mol-1). At -125°C ion 3 rearranges non-degenerately to the 1,4-bishomotropylium cation 1,8-dimethylbicyclo [4·3·0] nona, 2,4,7-trienyl (4) with k = 3 × 10-4 s-1. A mechanism for this rearrangement and the synthesis and purification of the ion precursor 4 are also reported.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030602
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    Correlation of molecular mechanics and NMR data: Conformation and configuration of the Meerwein lactones (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 419-427 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A method for relating averaged NMR parameters with point-by-point geometries for MM2 calculations is given for mobile molecules, e.g. δ-lactones. This method permits the identification of cis/trans geometry in cases where a complete set of isomers is not available. 2-Oxa-3r,4c,5t-triphenylcyclohexanone is prepared by condensation of 1,2-diphenylethanone with 3-phenylpropenal. The initially formed formed biscarbonyl adduct undergoes an internal Cannizzaro reaction forming a hydroxy ester, which lactonizes during work-up. The stereochemistry of the hydride transfer in the Cannizzaro reaction is consistent with the Felkin rule for asymmetric induction. The configurations of this and related lactones were studied through observation of NMR coupling constants, reductions to hemiacetals and molecular mechanics calculations. The most stable conformations are found to be a boat form for the parent lactone and a half-chair form for two isomers. The half-chair and boat forms lie near in energy for all isomers. The calculation techniques outlined illustrate that it is incorrect to consider only chair and boat forms; many intermediate conformations exist. Difficulties with previous IR methods of analysis are discussed.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030702
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    Thermochemical data of carbonyl compounds via their bond separation energies (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 443-448 
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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: Two types of equivalents for the aldo and the keto groups have been developed, the Schleyer and the bond separation energy (BSE) equivalents. The equivalents were used to give the heats of formation and the BSE of unstrained models. These equivalents were then used in the calculations of the strain energies for aldehydes and ketones. The results obtained were compared with MM2 values. The equivalents were also used in calculations of the stabilization (destabilization) energies for conjugated carbonyl compounds. The results obtained correlate well with the available experimental data.
    Additional Material: 5 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030705
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    Structure of 1,2,6-thiadiazine 1,1-dioxides (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 470-476 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ab initio theoretical calculations were carried out on the three tautomers, NH, OH and CH, of 1,2,6-thiadiazine 1,1-dioxides. Different basis sets were employed in order to obtain an adequate description of these cyclic sulphamide derivatives. A coherent picture is obtained which includes relative stability of tautomers (NH 〉 CH 〉 OH), non-planarity of NH and CH tautomers and electronic distribution (Boys' localized orbitals).
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030709
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    AM1 studies on the acid hydrolysis of acetamide (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 397-403 
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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 A2 hydrolysis of acetamide was investigated using the AM1 method and the results were compared with those of MNDO. The two methods agree in the general mechanism but differ in detail; MNDO assigns an unduly high energy for a complex with long bonds in contrast to AM1 and ab initio (at the 3-21G and 6-31G levels) methods, which predict a stable structure for such a complex. Inclusion of solvate water molecules has the effect of lowering activation barriers in general. An increase in the number of solving molecules up to four results in narrowing of the activation energy gap between the two rate determining steps of the A2 hydrolysis of the N- and O-protonated acetamide, but no reversal of the relative order of the barrier occurs; the A2 hydrolysis proceeding through the less stable N-protonated tautometer is therefore likely to remain as a major reaction path in solution-phase reactions, in agreement with experimental results.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030608
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610030701
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    Synthesis and spectroscopic properties of stereoisomeric 5,7-oxido-6-hydroxyiminocholestane derivatives (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 404-413 
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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 four possible diastereomeric 5,7-oxido-6-hydroxyiminocholestanes and their O-acetates have been synthesized. The stereochemistry of one of the latter has been proved unequivocally by x-ray diffraction. Their 1H and 13C NMR and also their circular dichroism spectra are discussed. It is now also possible to determine unequivocally the stereochemistry of the ring-junction geometry and the oxime E or Z stereochemistry.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030609
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    23Na nuclear magnetic resonance study of the complexation of sodium tetraphenylborate by [5,5]-dibenzo-30-crown-10 in nitromethane, acetonitrile, acetone and pyridine (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 435-442 
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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 nature of the (Na-DB30C10)+ complex has been studied by 23Na NMR in four non-aqueous solvents: nitromethane (NM), acetonitrile (AN), acetone (AC) and pyridine (PY). The equilibrium constant of formation (Kf) of (Na-DB30C10)+ in AC, AN and PY was determined at 300 K: log Kf = 3·9 ± 0·3, 3·4 ± 0·5 and 3·0 ± 0·1, respectively. In cases such as in pyridine, where exact values of the rate constants for the chemical exchange could not be calculated, limiting values were determined giving k-1 (the rate constant for complex dissociation) 〉 6·6 × 10-4 s-1 and kc (the rate constant for the formation of the complex) 〉 5 × 107 l mol-1 s-1. Evidence was found for the formation of a 2 : 1 (Na2-DB30C10)+2 complex in nitromethane. It has been previously shown that for (Na-DB24C8)+ the first coordination sphere of Na+ is exclusively filled by the oxygens of the crown ether, whereas for (Na-DB18C6)+ there is participation of at least one solvent molecule. The first coordination sphere of Na+ in (Na-DB30C10)+ consists of one or several molecules of solvent in addition to a number of oxygens from the crown ether. The soft wrapping of the Na+ by DB30C10 is in constrast with the hard wrapping of Na+ by DB24C8 and of K+ by DB30C10.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030704
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    N-Carbeniopyridinium salts: Charge-transfer complexes with the C5 (COOMe)5 anion; C—C bond formation with the TCNQ radical anion (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 459-469 
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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: N-[2,3-Bis(dimethylamino)cyclopropenylio]- and N-(tetramethylamidinio)pyridinium salts (trifluoromethanesulphonates and tetrafluoroborates) form 1:1 and 1:2 charge-transfer complexes with the pentakis(methoxycarbonyl)cyclopentadienide anion. The x-ray crystal structures of 1-[2,3-bis(dimethylamino)cyclopropenylio] pyridinium pentakis(methoxycarbonyl)cyclopentadienide tetrafluoroborate hydrate and of 1-[2,3-bis(dimethylamino)cyclopropenylio] pyridinium bis[pentakis(methoxycarbonyl)cyclopentadienide] were determined. In constrast, the tetra-cyano-p-quinodimethane (TCNQ) radical anion reacts with the first-mentioned salts by C—C bond formation to give novel dicationic salts. Thereby, the radical anion attacks the pyridinium γ-position of the N-(tetramethylamidinio)-pyridinium dication, but the three-membered ring of the N-[2,3-bis(dimethylamino)cyclopropenylio] pyridinium system.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030708
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    Kinetic and spectroscopy of 2-naphthylphenylcarbene (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 135-138 
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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: 2-Naphthylphenylcarbene (2-NPC) was studied by low-temperature EPR spectroscopy and by solution-phase laser flash photolysis. 2-NPC was found to have a triplet ground state with two distinct rotomeric forms. The triplet carbene was found to react with methanol, 1,1-diphenylethylene, styrene, carbon tetrachloride, isoprene, toluene and 2-methyltetrhydrofuran.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030210
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    Anomalous salt effects on a micellar-mediated reaction of bromide ion (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 239-247 
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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: Reaction of bromide ion with α-picryl-p-bromoacetophenone (1) is speeded by aqueous cationic micelles of cetyltrimethylammonium bromide (CTABr; C16H33NMe3Br) and dodecyltrimethylammonium bromide (DoTABr; C12H25NMe3Br) and rate constants reach limiting values when 1 is fully bound to micelles of CTABr. Limiting values are not reached in DoTABr, but the data can be fitted to a simple model for the distribution of reactants between water and micelles. Estimated second-order rate constants at the micellar surface are similar to values in water, but this model cannot explain the observed rate enhancements on addition of NaBr to CTABr. Inert anions such as nitrate, mesylate, n-butanesulfonate, phenylmethanesulfonate and camphor-10-sulfonate inhibit reaction in CTABr by competing with Br- at the micellar surface. Other n-alkanesulfonate ions (RSO3-, R = n-C5H11, n-C6H13, n-C7H15, n-C8H17) and arenesulfonate ions (benzene-, toluene-, naphthalene-1- and naphthalene-2-sulfonate) behave anomalously. These ions expel Br- from the micelle, as shown electrochemically, but there are maxima in plots of rate constant against mole fraction of Br-. These rate extrema are apparently due to perturbation of the micellar surface structure that overcomes the inhibition due to competition with Br-. These results show that the simple pseudo-phase, ion-exchange model can be applied only in dilute electrolyte and in the absence of hydrophobic anions.
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    URL: http://dx.doi.org/10.1002/poc.610030406
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610030301
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610030501
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    Mechanism of α-substitution reactions of acrylic derivatives (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 285-288 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reactions between acrylic esters, nitriles and similar compounds on the one hand and aldehydes and ketones on the other, catalysed by tertiary amines, lead to α-(hydroxyalkyl)acrylic compounds. Evidence on the basis of kinetics, volumes of activation and of reaction, and kinetic isotope effects is presented to deduce a mechanism in which amine first undergoes Michael addition, the resulting enolate ion adds to the carbonyl compound in a rate-determining step and finally base is eliminated. An analysis of the solvent effect on rates is also presented.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030503
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    β-Secondary deuterium isotope effect and solvent isotope effects in catalysis by subtilisin BPN′ (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 260-265 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Subtilisin BPN′ catalyzes the hydrolysis in protium and deuterium oxides of p-NO2C6H4OCOCL2NHCO2CH2C6H5(L = H, D) in the pH(D) range 5·0-8·5 (H2O) and 5·4-9·0 (D2O), according to simple Michaelis-Menten kinetics. The parameter kcat/Km exhibits pH(D) inflection points of 7·17 ± 0·05 (H2O) and 7·69 ± 0·08 (D2O), and kcat shows 6·88 ± 0·05 (H2O) and 7·50 ± 0·07 (D2O). The ‘normal’ ΔpK values of 0·5-0·6 indicate no unusual effects of D2O on enzyme properties. The solvent isotope effects (H2O/D2O) on the limiting values of the rate constants at high pH(D) are 1·13 ± 0·07 for kcat/Km and 1·29 ± 0·05 for Kcat. These small effects indicate no more than minor contributions of general acid-base catalysis for rate-limiting events for either kcat/Km or kcat. The β-deuterium secondary isotope effects (2H/2D) are roughly estimated by extrapolation as 0·95 ± 0·01 for kcat/Km, corresponding to substantial tetrahedral character in the transition state, and 1·03 ± 0·03 for kcat, consistent with no tetrahedral character. Models consistent with these results have as rate-limiting events for kcat/Km nucleophilic attack by active-site imidazole and for kcat, among other possibilities, the release of carboxylate product from the imidazolium form of the enzyme.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030409
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    Influence of structure on the isomerization of dialkylaminoalkylbenzotriazoles (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 289-294 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The N-1 to N-2 substituent isomerization in a series of 4-methyl and 4,7-dimethyl-N-(α-morpholinoalkyl)benzotriazoles and in 1,5-bis(morpholinomethyl)benzo [1,2-d:4,5-d′] bistriazole was studied and the influence of the structure on this process was evaluated.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030504
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    Inhibition of peroxidations of lipids and membranes by estrogens (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 309-315 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The antioxidant activity of 2-hydroxyestradiol was measured quantitatively and compared with those of other estrogens in oxidations of methyl linoleate in homogeneous solution and in aqueous dispersions, oxidations of soybean phosphatidylcholine liposomal membranes and oxidative haemolysis of rabbit erythrocytes, all induced by free radicals generated from a radical initiator. Similar antioxidant activities of estrogens were observed, irrespective of the oxidation system. 2-Hydroxyestradiol was found to be a potent radical scavenger and its antioxidant activity was close to that of α-tocopherol, the strongest natural antioxidant. Other phenolic estrogens such as estrone, estriol and β-estradiol showed a modest antioxidant activity and testosterone did not act as an antioxidant.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030507
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610030601
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  • 70
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    Gas-phase acidities of acrolein and methyl acrylate (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 346-348 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase acidities of acrolein and methyl acrylate were measured by bracketing in a flowing afterglow/SIFT apparatus. For acrolein ΔG°acid = 369 ± 4 kcal mol-1 and for methyl acrylate ΔG°acid = 373 ± 4 kcal mol-1. These acidities are substantially lower than those of the saturated analogs propionaldehyde and methyl acetate, respectively, even though hydrogens attached to sp2-hybridized carbon are intrinsically more acidic than those attached to sp3-hybridized carbon. Resonance stabilization of the neutral form by conjugation of the C=C double bond with the carbonyl group and allenic destabilization of the anionic form of the two acids can account for the relatively low acidities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030512
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  • 71
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    Stereochemistry and kinetics of thiophenoxide ion addition to methyl para-substituted phenylpropiolate derivatives in methanol. I (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 375-378 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactions of a series of methyl para-substituted phenylpropiolates with thiophenoxide ion in methanol were studied and their rates measured. Methyl β-thiophenyl esters were obtained as mixtures of Z and E isomers and their configurations were established by 1H NMR spectroscopy. Good Hammett correlations with ρ values of 1·57-1·97 were obtained, which suggest a carbanionic character of the transition state. A stepwise mechanism proceeding via an intermediate carbanion is postulated for this non-sterospecific addition reaction.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030605
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  • 72
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    Reaction of aryliminodimagnesium with diphenyl diketones: Heat evolution accompanying single electron transfer and chelate formation, and product distributionAryliminodimagnesium Reagents Part XVII. For Part XVI, see Ref. 1. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 379-389 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Reaction of diphenyl diketones (benzils) with aryliminodimagnesium [ArN(MgBr)2, IDMg], a magnesium reagent having condensation ability, was investigated. By comparison of the relative amounts of heat evolved in the reactions of IDMg (mildly electron donating) and ArMgBr (strongly electron donating) with some carbonyl and nitro compounds, results were obtained supporting the reported correlation of the relative yields of normal and abnormal (radical) products with single electron transfer (SET) efficiency estimated by the oxidation and reduction potentials of reactants. A sole exceptional result, i.e. the great heat evolution caused by the combination of benzil and IDMg, was attributed to the generation of tightly chelated radicals via SET. The involvement of stepwise SET was confirmed by ESR. On the basis of these results, substituent effects of benzil and mono-condensation products on their reduction potentials and on the relative yields of normal (mono- and di-condensation) and abnormal (dimerization) products were examined. All the results were consistently explained in terms of the relative efficiency of chelation (or σ-complexation) and SET in two main processes. The role of the initial stages involved in the processes governing the final product distribution is discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030606
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    Dephosphorylation by peroxyanions in micelles and microemulsions (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 390-396 
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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: Dephosphorylation of p-nitrophenyl diphenylphosphate (pNPDPP) by OH- in aqueous cationic micelles of cetyltrimethylammonium hydroxide (CTAOH) is inhibited by tert-butyl hydroperoxide (t-BuO2H), which reduces the binding of OH-, and whose anion is a relatively ineffective nucleophile. Reaction is faster in microemulsions of CTACl, n-octane and OH-, with t-BuO2H as cosurfactant, than in otherwise similar microemulsions with t-butyl alcohol as cosurfactant. Dephosphorylation by m-chloroperoxybenzoate ion is slower in microemulsions of cetyltrimethylammonium mesylate or benzenesulfonate, with n-octane and tert-butyl alcohol, than in cationic micelles, but a wide range of concentrations can be examined. The reaction rates qualitatively follow the concentration of peroxy acid relative to surfactant, and inert anions slow the reaction. Dephosphorylation by peroxyphthalate dianion in micelles of CTACl fits a pseudophase kinetic model, except in very dilute surfactant where reaction is faster than predicted.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030607
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    Homoallylic interaction of the double bond with substituents (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 477-481 
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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: Ab initio calculations were carried out on systems with a geometrically constrained relationship between a double bond and a homoallylic substituent X, as in YC=CCCX. The axial-equatorial equilibria in 3-substituted methylenecyclohexanes and 4-substituted cyclohexenes are determined largely by the homoallylic interaction between X and the double bond. The homoallyic substituent was chosen to be OCH3, and the nature of the double bond was varied by changing Y (H, CH3, F, Cl, CN). NMR experiments previously had found very significant dependences of the axial-equatorial equilibrium on the nature of the X and Y substituents. Electrostatic calculations, based on Mulliken charges, reproduce the experimental (NMR) substituent effects on the axial-equatorial equilibrium and suffice to explain all the observations.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030710
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    Structural studies of halogen adducts of some cyclic selenides and tellurides by 1H, 13C, 77Se and 125Te NMR. Evidence for the formation of molecular complexes of selenoxanthone and selenanthrene with bromineFor a preliminary contribution, see Ref. 1. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 369-374 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 1H, 13C, 77Se and 125Te NMR spectra were recorded for selenoxanthone (1a), telluroxanthone (2a), selenanthrene (3a), related compounds and their halogen adducts to elucidate the structure of the adducts in solutions. Although selenides react with bromine to give trigonal bipyramidal (TB) hypervalent complexes in general, 1a reacted with bromine to yield a molecular complex (MC). Its chlorine adduct was found to be a TB. The effective electronegativity of selenium in 1a may be modulated by conjugation with the strongly electron-withdrawing carbonyl group. In the case of 2a, its halogen adducts were TBs. The structure of the bromine adduct of 3a was also demonstrated to be an MC from NMR data.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030604
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    Correlations of rate and selectivity of a Diels-Alder reaction with Sp parameters (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 414-418 
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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 rate and endo/exo selectivity of the Diels-Alder reaction between cyclopentadiene and methyl (E)-α-cyanocinnamate at 25°C, in several acetone-water and 1,4-dioxane-water mixtures, were measured. The linear correlations of log k and log(endo/exo) vs solvophobicity are reported. Correlations for selectivity are considerably improved when the results obtained in acetone-water and 1,4-dioxane-water are taken as separate series.
    Additional Material: 5 Ill.
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610030901
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    Frequency-dependent branching ratio in the infrared multiphoton photochemistry of diethyl carbonates (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 567-574 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Unimolecular decomposition of 0·1 Torr of diethyl carbonate, diethyl-d5 carbonate and diethyl-d10 carbonate induced by irradiation with a CO2 TEA laser was investigated. In all cases only ethylene, ethanol and CO2 were obtained. In the case of diethyl-d5 carbonate, both ethylene-d4 and ethylene-d0 were observed together with the corresponding isotopic variants of ethanol. The chemical branching ratio was determined as a function of irradiation frequency and laser fluence by analysis of the ethylene-d0/ethylene-d4 ratio. RRKM theory applied to the branching ratio data requires very different average energies for two sets of fluence and frequency conditions that give identical total yields.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030903
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    NMR spectroscopic study of configurations and conformations of 5-pyridylmethylenehydantoins (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 559-566 
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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: Nine 5-pyridylmethylenehydantoins were prepared. Each of the 1-methyl-substitute compounds was obtained in two stereoisomeric forms. Only one form of each of the 3-methyl-substituted and N-unsubstituted compounds was obtained directly from synthesis but could be partially converted into the other stereoisomer photochemically. The Z/E configurations and the conformational relationship between the pyridine and hydantoin rings were studied by 1H and 13C NMR spectroscopy, including variable-temperature 1H NMR. The existence of N—H…N or C—H…N interactions and the possibility of tautomerism are suggested for some of the compounds. The Z-isomers of compounds with 2- or 3-pyridyl rings prefer an s-cis conformation whereas the E-isomers prefer an s-trans conformation.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030902
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  • 80
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    A valence and charge criterion for reactivity of π electron systems (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 599-605 
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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 new criterion for the reactivity of π electron systems is proposed. The method incorporates and modifies ideas of Coulson and Fukui et al. about free valence. The proposed reactivity index includes covalent and lonic components and is suitable for elctrophilic, radical and nucleophillic attack. The method is tested for a few simple π systems and differences from Coulson and Fukui et al. are discussed. Finally, it is applied to the electrophilic attack of a series of substituted benzenes and to nucleophilic attack of a series of subsituted benzoic acid esters.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030908
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    General-acid, specific-base and intramolecular catalysis of the dehydration step in nitrone formation from furfurals and phenylhydroxylamine (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 620-626 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nitrone formation from furfural and 5-nitrofurfural with phenylhydroxylamine was studied in water at 25°C and ionic strength 1·0 (KCl). The reaction exhibits general acid catalysis (α = 0·52), specific base catalysis and a pH-independent process. The results are consistent with a mechanism where dehydration of an N,N′-dihydroxy addition intermediate, formed by a rapid pre-equilibrium, is the only rate-determining step over the pH range studied (1-11). In contrast, nitrone formation from p-chlorobenzaldehyde and N-methylhydroxylamine exhibits a clear change of rate-determining step, from dehydration of the addition intermediate to attack of the nucleophile on the aldehyde, with increase in pH. The profile of log k2 (k2 = second-order rate constant) vs pH indicates, by comparison with the corresponding profile for similar reaction, that phenylhydroxylamine exhibits unexpected nucleophilic behaviour in this reaction. The pH-indpendent dehydration process, which has a higher rate constant than that predicted from the Brønsted line for the water catalysis, appears to involve intramolecular catalysis rather than bifunctional catalysis by water.
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    URL: http://dx.doi.org/10.1002/poc.610030911
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    Role of 2-carboxyl substituent in the tautomerization between two equivalent enol forms of 3-hydroxyphenalenone (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 485-488 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The interconversion between two equivalent enol forms of 3-hydroxyphenalenone took place predominantly through a diketo form with a free energy of activation of ca 14 kcal mol-1 in DMSO solution determined by 125·8 MHz13C NMR measurement. On the other hand, the corresponding interconversion in 2-carboxy-3-hydroxyphenalenone was not frozen on the time scale of 13C NMR spectroscopy down to -60°C. This acceleration in the interconversion rate of the latter may be interpreted by a double proton switching between the hydrogen-bonded 2-carboxyl and 3-hydroxyenone moieties.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030712
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    Cross-interaction constants as a measure of the transition state structure. Part 8. Mechanism of the reaction of 2-phenylethyl benzenesulphonates with benzylamine in acetonitrile (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 545-549 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of reactions between 2-phenylethyl benzenesulphonates (2-PEB) and benzylamines in acetonitrile at 65·0°C have been studied; the mechanism was examined on the basis of the sign and magnitude of cross-interaction constants ρij and βij. In contrast to the reactions of 2-PEB with anilines in methanol, participation of the aryl-assisted pathway was negligible, with a strong indication that the reaction proceeds largely by an intermolecular SNi mechanism with a four-centre transition state (TS). The effect of substituents on the TS variation was in accord with the predictions of the quantum mechanical model.
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    URL: http://dx.doi.org/10.1002/poc.610030808
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    Origin of exo selectivity in norbornene. An ab initio MO study (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 519-533 
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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 geometries of the reactants, the reactant π-complex, the transition state and the product for exo and endo addition of BH3 to norbornene were optimized at the HF/3-21G level, and their energies were calculated at the MP2/6-31G level. The analysis of activation energy and model calculations singled out the endo deformability, a major portion of the norbornene deformation energy, as the origin of exo selectivity; norbornene, with the olefinic hydrogens already bent toward endo in the equilibrium geometry, requires less deformation to reach the exo than the endo transition state. The reason why olefinic hydrogens are bent in norbornene has been elucidated. An analysis indicates that the difference between norbornene exo side and bicyclo [2.2.1] hex-2-ene is also dictated by the endo deformability.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030806
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    Interpretation of 1H NMR spectra of 2-benzopyrylium salts with the use of the CNDO/2 method (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 575-580 
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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 1H NMR spectra of eleven substituted 2-benzopyrylium salts are interpreted with the aid of the CNDO/2 method for standard geometry. Some effects of the substituents are considered for the charge distribution in the 2-benzopyrylium cation.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030904
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    Roles of kinetic and potential energies in conjugation II.For Part I, see Ref. 1. Aniline and nitrobenzene (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 587-593 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An analysis of the energy components of the conjugation energy between the substituent and the phenyl group in aniline and nitrobenzene showed that there are two types of conjugation: the conjugation energy in aniline, with an electron-donating substituent, is given by the decrease in the kinetic energy of elctrons, whereas that in nitrobenzene, with an electron-withdrawing substituent, is caused by the decrease in the potential energy. Physical interpretations are given of the arrows in the organic electron theory of these compounds.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030906
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    Theoretical study of the gas-phase thermal isomerization of isoxazoles. Part I. Isoxazole (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 611-619 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An MNDO study was made of the gas-phase thermal isomerization of isoxazole to explore theoretically the proposed reaction mechanism. The results showed that isoxazole isomerizes through an azirine, as an intermediate, to oxazole via a nitrile ylide or to ketenimine, with similar activation energies, and that the first step is rate limiting, in agreement with the experimental results. These results also show that isomerization to a nitrile is possible, but in this case the energy barrier is grater than the corresponding isomerization to oxazole. The MNDO study also supports a concerted process for the rate-limiting step, as reported earlier on the basis of experimental studies.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030910
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  • 88
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    Electronic Resource
    Electronic absorption spectra of aliphatic diamine radical cations. Conformation-dependent charge delocalization (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 606-610 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Electronic absorption spectra of radical cations generated by steady-state and pulse radiolysis from a series of α,ω-diaminoalkanes (R2N(CH2)nNR2; n = 1-6, R = CH3 or C2H5), 1,4-dimethylpiperazine and 1,4-diazabicyclo [2.2.2] octane (DABCO) were measured. In some cases spectral evidence was obtained for an interaction between the nitrogen atoms leading to charge delocalization in the radical cation. A delayed formation of radical cations was associated with a conformational change necessary for achieving the most stable structure having a favourable conformation for charge delocalization.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030909
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  • 89
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    Electronic Resource
    Effects of the heteroaromatic moiety on spectroscopic properties, pKa and reactivity of azoles: A chemometric study (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 651-658 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The spectroscopic and physicochemical properties of parent azoles substituted on the nitrogen by a proton, a methyl group, a p-aminophenyl group and an acetyl group have been gathered. This information on azol-1-yl substituents has been treated by principal component analysis and partial least-squares analysis. The first result of these analyses is that it has been possible to complete some missing properties of azol-1-yl substituents, such as pKa for proton loss of some azoles and hydrolysis rates of certain azolides. Another significant result of the chemometric approach is the assignment of the 1-acetyltetrazole IR and NMR data to one of the two possible isomers.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610031006
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  • 90
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    The spin delocalization substitutent parameter σJJ. 5. Correlation analysis of 19F chemical shifts of substituted trifluorostyrenes. The unresolved polar substituent parameter σmb (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 643-650 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 19F NMR spectra of 30 substituted α,β,β-trifluorostyrenes (Y-TFSs, 1) covering a diverse range of substituents are reported and discussed. Values (δF1, δF2, Δδ3 - 1 and Δδ3 - 2) derived from the 19F NMR chemical shifts of the fluorine atoms of 1 are found to correlate very well with σI and σR0. The results of the correlations of the 19F chemical shifts with dual (σF and σR) and triple parameter (σF, σR and σα) treatments are compared. An unresolved substituent parameter σmb, is proposed for applications to systems in which the substitutent Y interacts with a multiple bond and is compared with σ+.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610031005
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  • 91
    Electronic Resource
    Electronic Resource
    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    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.610031201
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  • 92
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    Solvation of indenyllithium and indenylpotassium studied by 13C NMR spectroscopy (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 9-12 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polarization of the π-electron systems of indenyllithium (In -Li+) and indenylpotassium (In -K+), which is generally indicative of the degree and tightness of contact ion pairing, was investigated by 13C NMR spectroscopy. The effect of changing solvent is about two thirds as great for In -K+ as for In -Li+. The indenyl anion is more strongly polarized with Li+/dimethyl sulfoxide than with Li+/ammonia, whereas the reverse is observed for In -K+. Complexation of In -K+ in tetrahydrofuran (THF) by cryptand(2,2,2) results in a π-electron distribution identical with that of In -Li+ in hexamethylphosphoramide, indicative of solvent- or agent-separated ion pairs or free ions. Small but significant cation-anion interactions are observed for In -K+ in hexamethylphosphoramide and for In -N+Me4 in THF.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030103
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  • 93
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    Electronic Resource
    Structure and stability of 2σ/1σ* three-electron-bonded radical cations from 1,n-bis(alkylthio)alkanes in aqueous solutions (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 17-22 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A large number of 1,n-bis(alkylthio)alkanes, R′S(CH2)nSR″, was investigated by pulse radiolysis in aqueous solutions. The sulphur-centred radical cations, which were obtained on oxidation of the dithia compounds by ·OH radicals, are stabilized via 2σ/1σ* three-electron interaction between two sulphur atoms. Intramolecular stabilization is the only process observed for n = 2-4, whereas for longer chain compounds with n 〉 4 some intermolecular sulphur-sulphur interaction is also indicated. The stability and yields of the three-electron-bonded species also depend on the nature of the substituents R′ and R″, and for the intermolecular systems are a function of solute concentration. The results corroborate earlier investigations and demonstrate, in particular, that the optical parameters are a very sensitive measure of changes in electron density and structure of the three-electron-bonded systems.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030105
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  • 94
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    Stereochemistry of silver-ion-assisted solvolysis of tert-butylphenylphosphinothioic iodidate. Phosphathiacylium cation formation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 35-37 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Studies on the stereochemistry of silver-ion-assisted solvolysis of a new optically active tert-butylphenylphosphinothioic iodidate demonstrated that the reaction proceeds with inversion of configuration at the phosphorus atom. Evidence for phosphathiacylium cation formation as a reactive intermediate is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030107
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  • 95
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    Electronic Resource
    Mechanisms of aromatic nucleophilic substitution reactions in ethyl acetate and tetrahydrofuran (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 41-47 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the reactions of 1-chloro-, 1-fluoro- and 1-phenoxy-2,4-dinitrobenzene with piperidine, n-butylamine and benzylamine, and in the case of the ether, morpholine were studied as functions of nucleophile, DABCO and pyridine concentrations in tetrahydrofuran and ethyl acetate. The reactions of the ether with n-butylamine and benzylamine in benzene were also studied as functions of nucleophile, DABCO and pyridine concentrations. A comparison with results in the literature indicated that the reactions in tetrahydrofuran and ethyl acetate resemble those in dipolar aprotic solvents when primary amines are the nucleophiles and those in aprotic solvents when the nucleophile is a secondary amine. An explanation is suggested for the observation that whereas the reactions of 1-phenoxy-2,4-dinitrobenzene with piperidine and morpholine in both tetrahydrofuran and ethyl acetate are strongly catalysed by the nucleophiles, they are not catalysed by pyridine and there is either extremely weak or no catalysis by DABCO.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030109
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  • 96
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    Gas-phase nitration of thiophene and N-methylpyrrole by protonated alkyl nitrates (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 110-118 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase nitration of thiophene (1) and N-Methylpyrrole (2) was studied by radiolytic tecniques, supported by chemical ionization mass spectrometry. The substrate and positional selectvities of protonated alkyl nitrtes (CH3NO3H+, CF3CH2NO3H+) were deduced from competitive reactions with bezene performed under different conditions. The apparent kS/kB ratios, which are independent of the pressure and unaffected by the presence of a strong base (NEt3), depend on the nature of the electrophile, passing for 1 and 2 from 7·2 and 6·4, respectively, with CH3NO3H+ to 1·1 and 1·0, respectively, with the more reactive fluorinated caution. Predominant (88%) α-substitution takes place in 1, whereas no appreciable positional discrimination is displaced by 2. The results suggest that the electrophilic attack can also occur a the heteroatom, and point to the same mechanism postulated for gasphase nitration of aromatic substrates, the reactivity being essentially governed by electrostatic interactions within the ‘encounter pair’.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030207
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  • 97
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    Hydration of 2,2-dichloro-1-arylethanones in water and tetrahydrofuran-water mixtures (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 89-94 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The hydration of 2,2-dichloro-1-arylethanones was studied in water and tetrahydrofuran (THF)-water mixtures and the equilibrium constants in water were estimated for four ethanones. The process is subject to specific acid and to general base catalysis. The proton inventory technique was applied to the study of the reaction in L2O and THF-L2O solutions (L = H or D). In pure water and water-rich mixtures, a very large number of protons participate in the open transition state, this number decreasing gradually with increasing water content in the mixture, until the minimum value of 2 is reached, corresponding to a cyclic, closed transition-state structure.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030205
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  • 98
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    Electronic Resource
    Consecutive radical ion pairs in the cycloreversion of a dimethylindene dimer: A case of cooperative spin polarization effects (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 119-125 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Nuclear spin polarization effects observed during the electron transfer-induced cleavage of the trans head-to-head dimer of 3,3-dimethylindene are incompatible with the intermediacy of a single dimer radical cation. Instead, they are compatible with the ‘cooperative’ involvement of a localized, doubly linked and a delocalized, singly linked dimer radical cation. The mechanistic consequences for the cycloaddition and cycloreversion of radical cations are discussed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030208
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  • 99
    Electronic Resource
    Electronic Resource
    Additivity of bond separation energies of hydrocarbons and their thermochemical data (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 126-134 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The additivity of experimental bond separation energies is demonstrated. This thermodynamic function can be reproduced by summation of group equivalents with a correction for the ‘stabilization’ energy. For this purpose, several group equivalents have been developed for alkanes and alkenes. The correlation between the computed and the experimental bond separation energies is good. These equivalents are then used in evaluating the stabilization (destabilization) energies for aromatic hydrocarbons and polyenes. The results obtained are in good agreement with values reported in the literature.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030209
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  • 100
    Electronic Resource
    Electronic Resource
    Organophosphorus herbicides and plant growth regulators part 1. Synthesis and protonation behaviour of glyphosate and related compounds (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 248-254 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ionization constants of N-phosphonomethylglycine (glyphosate) and three structurally related plant-growth regulators were determined by potentiometric titration. The effect of pD on the chemical shifts of the 1H and 13C nuclei of the methylene groups and of the 31P nucleus in these substrates was measured by NMR spectroscopy. The results allowed an assignment to be made of a specific site (carboxylic, phosphonic, ammonium) in the molecule to each of the determined pKa values.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030407
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