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  • 1
    Electronic Resource
    Electronic Resource
    Chlorosilanes: Development and application of MM2 force field parameters (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 10 (1989), S. 832-849 
    Details
    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, relative conformational energies, and dipole moments of mono and polychlorosilanes have been calculated using ab initio molecular orbital (MO) theory. Calculations at the HF/3-21G(*) level, with the exception of dipole moments, give reasonable agreement with experimental data. A new MM2 force field for chlorosilanes, which includes terms for bond length shortening and bond angle compression due to the attachment of electronegative Cl atoms, has been developed on the basis of experimental and ab initio results. The new force field is generally successful in predicting structural parameters, but is unable to reproduce the dipole moments of several model systems. While dipole moment predictions are not the authors' main interest, this failure defines a shortcoming in the MM2 method. The new parameters have been applied to problems in the prediction of stereochemistries of cyclic systems, and compared with experimental results where data are available.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540100606
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Rotational barriers of disilane, hexafluorodisilane, and hexamethyldisilane: Ab initio, density functional, and molecular mechanics (MM3) studies (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 1523-1533 
    Details
    ISSN: 0192-8651
    Keywords: barrier ; silicon ; disilane ; ab initio ; density functional ; molecular mechanics ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We investigated structures, vibrational frequencies, and rotational barriers of disilane (Si2H6), hexafluorodisilane (Si2F6), and hexamethyldisilane (Si2Me6) by using ab initio molecular orbital and density functional theories. We employed four different levels of theories (i.e., HF/6-31G*, MP2/6-31G*, BLYP/6-31G*, and B3LYP/6-31G*) to optimize the structures and to calculate the vibrational frequencies (except for Si2Me6 at MP2/6-31G*). MP2/6-31G* calculations reproduce experimental bond lengths well, while BLYP/6-31G* calculations largely overestimate some bond lengths. Vibrational frequencies from density functional theories (BLYP/6-31G* and B3LYP/6-31G*) were in reasonably good agreement with experimental values without employing additional correction factors. We calculated the ΔG
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 3
    Electronic Resource
    Electronic Resource
    Proton-transfer reactions within ionized methanol clusters: Mass spectrometric and molecular orbital studies (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 969-976 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Proton-transfer reactions that proceed within methanol cluster ions were studied using an electron impact time-of-flight mass spectrometer. When CH3OH seeded in helium is expanded and ionized by electron impact, the protonated species, (CH3OH)nH+, are the predominant cluster ions in the low-mass region. In CH3OD clusters, both (CH3OD)nH+ and (CH3OD)nD+ ions are observed. The ion abundance ratios, (CH3OD)nH+/(CH3OD)nD+, show a tendency to decrease as the methanol concentration increases, which is apparently related to the cluster structure and reaction energetics. The results suggest that the effective formation of (CH3OD)nH+ ions at low concentration of CH3OD in the expansion is the result of the relatively facile rotation of methanol molecules within the smaller clusters that tend to form at low CH3OD concentration. Ab initio molecular orbital calculations were carried out to investigate the rearrangement and dissociative pathways of ionized methanol dimer. Ion-neutral complexes, [CH3OH2+…O(H)CH2] and [CH3OH2+…OCH3], are found to play an important role in the low-energy pathways for production of CH3OH2+ + CH2OH (and OCH3) from ionized methanol dimer.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300706
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    Paper (German National Licenses)
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