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  • 1
    Unknown
    Berlin, Heidelberg : Springer
    Keywords: Biochemistry ; Chemistry ; Chemistry, Organic ; Chemistry, inorganic
    ISBN: 9783540314448
    Language: English
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 7 (1986), S. 93-104 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Heats of formation of 119 closed- and open-shell carbocations calculated by the semiempirical quantum chemical methods MINDO/3 and MNDO are reported and compared with experimental data. With proper consideration of failures in specific areas, both methods can be used for the thermodynamics of carbocations containing C, H, N, and O. MINDO/3 predicts unrealistic values for nitrogen containing cations with nitrogen multiple bonds and is not suited for closed-shell cations containing oxygen. Saturated acyclic hydrocarbon radical cations often are computed with abnormally long CC bonds by MNDO. Otherwise, the standard deviation of the two methods is not very different, being in the range of ±13 kcal/mol. MINDO/3 tends to overestimate the cation stabilities, whereas MNDO calculates cations usually too high in energy. Some of the errors which were found in the calculations of the ions are related to the computed values for the parent neutral structures, but others are not.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 6 (1985), S. 189-199 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio MO calculations have been performed for neutral and cationic C2H2F2 structures. Olefinic and carbene structures are investigated for the neutral isomers, while olefinic, carbene, and fluoronium-type cations are found. Stability orders and rotational barriers are discussed in terms of orbital and Coulomb interaction. Contrary to previous studies, the higher stability of the geminal isomers is interpreted to be caused by Coulomb attraction.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 1184-1198 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The geometries and dissociation energies for the Fe—C and C—H bonds of FeCHn and FeCHn+ (n = 1, 2, 3) have been calculated by ab initio quantum mechanical methods using different effective core potential models and Møller-Plesset perturbation theory. The HW3 ECP model, which has a configuration [core] (n-1)s2, (n-1)p6, (n-1)d1, (n)sm for the transition metals, is clearly superior to the larger core LANL1DZ ECP model with the configuration [core] (n-1)d1, (n)sm. The Fe—C bond energies calculated at correlated levels using the HW3 ECP are in much better agreement with experiment than the LANL1DZ results. This effect is mainly due to the higher number of correlated electrons rather than the inclusion of the outermost core electrons in the Hartree-Fock calculation. At the PMP4/HW3TZ/6-31G(d)//MP2/HW3TZ/6-31G(d) level, the theoretically predicted Fe—C bond energies for FeCHn+ are in the range of 80% of the experimental values and have nearly the same accuracy as all-electron calculations using large valence basis sets and the MCPF method for the correlation energy. © 1992 by John Wiley & Sons, Inc.
    Additional Material: 20 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 3 (1982), S. 251-259 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The structures and rearrangements of various cyclic and acyclic C4H8NO+ cations resulting from the title reaction have been investigated by means of semiempirical (MNDO) and ab initio (4-31G) calculations.
    Additional Material: 3 Tab.
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  • 6
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The optimized geometries and energies of fluorine-substituted ethylene dications C2HnF4-n 2+ (n = 0-4) have been investigated by means of ab initio methods. At the MP3/6-31G**//6-31G* + zero-point energy level of theory, the results predict that C2F42+ and C2HF32+ are planar, while C2H42+, C2H3F2+ and 1,1 - C2H2F22+ prefer a perpendicular geometry. For 1,2 - C2H2F22+ an energy difference of only 0.3 kcal/mol is found between the (trans) planar and perpendicular structure. The stabilizations attributed to hyperconjugation, fluorine lone-pair donation, and (C—F) double-bond conjugation are discussed. A comparison is made for the C—C and C—F stretching frequencies determined at 6-31G*//6-31G* between the neutral and dicationic species. The theoretically determined ionization energies for the vertical process N+ → N2+ at the MP3/6-31G*//3-21G level are compared with experimental Qmin values.
    Additional Material: 3 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 919-934 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The performance of effective core potentials (ECP) and model potentials (MP) has been studied by calculating the geometries and reaction energies of isodesmic reactions for the molecules Ti(CH3)nCl4 - n (n = 0-4) at the Hartree-Fock level of theory. The results are compared with data from all electron calculations and experimental results as far as available. The all electron calculations were performed with a 3-21G basis set from Hehre and a (53321/521/41) basis set from Huzinaga. For the ECP calculations the potentials developed by Hay and Wadt, and for the MP calculations, the model potentials developed by Sakai and Huzinaga, are employed. © 1992 by John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 935-943 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The performance of effective core potentials (ECP) for the main group elements of group IV has been studied by calculating the geometries and reaction energies of isodesmic reactions for the molecules M(CH3)nCl4 - n (M = C, Si, Ge, Sn, Pb; n = 0-4) at the Hartree-Fock level of theory. The results are compared with data from all electron calculations and experimental results as far as available. The all electron calculations were performed with a 3-21G(d) and a 6-31G(d) basis set for Si, a (43321/4321/41) basis set for Ge, and a (433321/43321/431) basis set for Sn. For the ECP calculations the potentials developed by Hay and Wadt with a configuration (n)sa(n)pb and the valence basis set (21/21), extended by a set of d functions, are employed. © 1992 by John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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