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  • Computational Chemistry and Molecular Modeling  (3)
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  • Computational Chemistry and Molecular Modeling  (3)
  • Biochemistry  (3)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 10 (1989), S. 99-103 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: For a series of simple alkyldisilanes, 3-21G (*) full gradient geometry optimizations have been performed to yield both structural and conformational energy data which was suitable for calibrating the MM2 force field for disilanes. We have examined several model structures which yielded sufficient information about the rotational potential around the Si-Si bond to enable us to revise and augment those reported by Frierson. These parameters were questioned by us in the course of MM2 studies of 1,2-disilacyclobutanes. We report new Si-Si torsion parameters as well as pertinent structural data from 3-21G(*) geometry optimizations and relative conformational energies derived from Møller-Plesset (MP2/MP3) calculations at the 6-31(*)/3-21G(*) level. The new parameters were applied to the 1,2-dimethyl-1,2-disilacyclohexane system and those results are also reported.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 10 (1989), S. 832-849 
    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
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  • 3
    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 calculations at several basis set levels were used to examine the rotational potential energy function around the C—C bond of 1,2-disilylethane, also known as disilabutane (DSB). The best basis set for this system was found to be the 3-21G(*) basis, which was also used to verify the potential function around the CH2 - SiH2 segment in ethylmethylsilane (EMS). The torsional parameters developed by Frierson and Allinger for the C—Si—C—C fragments were shown to yield a potential in excellent agreement with those from the 3-21G(*) basis. Full 3-21G(*) geometry optimizations were performed on the 0°, gauche (60°), and 180° conformers of DSB and EMS. Data derived from the ab initio calculations on DSB were used to establish MM2 torsional and bond length parameters for the Si—C—C—Si fragment. The MM2 and ab initio structures agree well. A detailed comparison of rotational potentials and the steric energy components is presented. We also report the torsional potential of propylsilane (PS) and compare the MM2 calculated structure with experiment. Our findings suggest that the similarity of the torsional potentials of butane and DSB and the dissimilarity between butane and EMS arise from the same phenomenon - van der Waals interactions that are attractive rather than repulsive dominant.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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