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  • 1
    Electronic Resource
    Electronic Resource
    Nonempirical analysis of unusual chemical bonds. II. AlH2BH4 and AlH2C3H5 (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 1197-1201 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio computations have been performed on the compounds AlH2BH4 and AlH2C3H5 in order to achieve a better understanding of the peculiar characteristics of the metal to ligand bond. Our results suggest a bidentate coordination for the tetrahydroborate complex and an η3 coordination for the allyl complex. Due to the nonrigidity of the BH4- and allyl complexes, possible interconversion paths between different coordination modes have also been analyzed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560190632
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The mechanisms of elementary physicochemical processes: An introductory report (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 563-591 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Most of the work of theoretical physical chemists and chemical physicists relates at least indirectly to the mechanisms of physicochemical processes. Therefore it is important to examine the meaning and the scope of that notion in the context of recent developments in computational studies. After a brief mention of the meaning of the expression “elementary” physicochemical processes (EPCP), the authors adopt as a definition of mechanism a cause - effect description of an EPCP based on metastable and transient states corresponding to minima and saddle points of the potential energy surface; these states transform into one another according to appropriate selection rules. The so-called reaction-path Hamiltonian can be seen as the starting point for a quantum interpretation of the mechanism concept. On this basis the reaction coordinate, the mechanism profile, and the transition state can be fitted into the same framework. Selection rules are illustrated on the symmetry rules, with a few recent examples of applications which also show their limitations. “Propensity” rules allowing surmises on the nature of a transition state from a static picture of the initial state are also considered and their connection with “reactivity indices” emphasized. Processes involving excitation of electronic states as well as environmental effects are briefly examined. Finally, a specific example taken from surface studies is described in some detail to provide the grounds for further reflection.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560260503
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  • 3
    Electronic Resource
    Electronic Resource
    Gas phase unimolecular 1,1-hydrogen elimination: Reaction mechanism and isotope effect (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 621-636 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism of unimolecular 1,1-elimination of H2 from carbocations has been investigated by the semiempirical MNDO method in view of its very good performances in the analogous elimination from H2CO. Contrary to previous suggestions, the critical configuration obtained at the MNDO level is characterized by a reduced symmetry with respect to the reacting molecule and by a very short H—H distance. RRKM computations of the rate constants and isotope effect employing MNDO results for the activation energies and vibrational frequencies indicate also that the present, nonsynchronous mechanism is compatible with all the available experimental data.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560260506
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  • 4
    Electronic Resource
    Electronic Resource
    Charge transfer in adsorbate-substrate systems: Extension of the Anderson-Newns treatment to two- and three-dimensional substrates (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 769-774 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Charge transfer in adsorbate-substrate systems has been studied in the limiting case of an unperturbed substrate extending the Anderson-Newns treatment to two- and three-dimensional substrates. This allows comparison of different chemisorption sites within an essentially analytic treatment. Important changes of the local densities of states with respect to the usual one-dimensional model are obtained. The resulting charge transfers are of the same order of magnitude as those obtained by adding correlation effects to the one-dimensional Anderson-Newns model.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560260516
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  • 5
    Electronic Resource
    Electronic Resource
    Conformational behavior of azabiphenyls (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 541-551 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational behavior of biphenyl-like compounds constituted by benzene and/or azabenzenes has been investigated at the STO-3G Hartree-Fock level. Although the STO-3G basis set probably overstimates conjugative attraction, it seems able to provide reliable general trends. In this connection the analysis of over 30 molecules shows that compounds with the same ortho substituents (including nitrogen lone pairs) have very similar conformational behavior, irrespective of their composition. Furthermore, the comparison of different isomers shows that repulsive interactions decrease in the order hydrogen-hydrogen 〉 lone pair - lone pair 〉 hydrogen lone pair. Conjugative, electrostatic, and steric interactions have also been expressed by well known semiempirical functions, thus allowing a better analysis of the overall torsional potential.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290326
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical energies of representative carbon-carbon bonds (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 55 (1995), S. 469-476 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A bond-energy formula deduced by means of the Hellmann-Feynman theorem is applied to selected simple hydrocarbons. The required potentials at the nuclei are calculated with the help of large basis-set expansions including polarization functions. The carbon-carbon bond energy of ethane is evaluated at ∼ 70 kcal mol-1. The CC bond energies of ethane, ethylene, acetylene, benzene, and cyclopropane are approximately in a ratio of 1: 2.0: 3.0: 1.65 1.0. Limitations and possible improvements in future applications of this energy formula are discussed. © 1995 John Wiley & Sons, Inc.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560550605
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  • 7
    Electronic Resource
    Electronic Resource
    Density functional theory: An effective theoretical tool for the study of σ radicals (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 963-971 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structures, harmonic force fields, and hyperfine coupling constants of a number of representative σ radicals have been investigated by the density functional approach including nonlocal corrections. Scaling of CH bond lengths and stretching constants leads to accurate structures and force fields. Hyperfine coupling constants reach, at least, the level of the most sophisticated conventional post-Hartree-Fock models. This suggests that the density functional approach is a promising theoretical tool for the study of relationships between structure and spectroscopic properties of large free radicals. © 1994 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520422
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  • 8
    Electronic Resource
    Electronic Resource
    Proton transfer in small model systems: A density functional study (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 697-705 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structures, interaction energies, and proton-transfer features of some representative intermolecular complexes are determined by using a density functional which incorporates gradient corrections and, as recently suggested by Becke, some Hartree-Fock exchange. The results are compared with those obtained by high-order many-body perturbation theory and by a number of more conventional density functionals. Hydrogen-bond strengths and interatomic distances between heavy atoms are well reproduced by several density functionals. However, inclusion of some Hartree-Fock exchange is mandatory to improve XH bond lengths, and, especially, energy barriers governing proton transfer. Use of the new functional significantly improves the agreement with experimental and post-Hartree-Fock results. This paves the route for a detailed theoretical study of proton-transfer processes in large, biologically significant systems. © 1995 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560607
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