Volume 100, Issue 5 pp. 720-732
Properties, Dynamics, and Electronic Structure of Atoms and Molecules

Relative energies, stereoelectronic interactions, and conformational interconversion in silacycloalkanes

Fillmore Freeman

Corresponding Author

Fillmore Freeman

Department of Chemistry, University of California, Irvine, CA 92697-2025

Department of Chemistry, University of California, Irvine, CA 92697-2025Search for more papers by this author
Christine Fang

Christine Fang

Department of Chemistry, University of California, Irvine, CA 92697-2025

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Bagrat A. Shainyan

Bagrat A. Shainyan

A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of the Russian Academy of Science, 1 Favorsky Street, 664033, Irkutsk, Russian Federation

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First published: 17 August 2004
Citations: 27

This article contains supplementary material available via the Internet at http://www.interscience.wiley.com/jpages/0020-7608/suppmat.

Abstract

Stereoelectronic hyperconjugative interactions, geometrical parameters, and relative energies of conformations and isomers of silacycloalkanes have been calculated at the B3LYP/6-311+G(d,p) level of theory. The chair conformer of silacyclohexane was calculated to be 3.89, 4.82, and 5.18 kcal/mol more stable than the respective 1,4-twist conformer, 2,5-twist conformer, and 2,5-boat transition state. Intrinsic reaction path (IRC) calculations connected the half-chair transition state to the chair and 2,5-twist conformers of silacyclohexane. The energy difference (ΔE) between the chair conformer and the half-chair transition state that connects the chair conformer and 2,5-twist conformer of silacyclohexane is 5.47 kcal/mol. The chair conformer of equatorial 1-methyl-1-silacyclohexane is 0.45 kcal/mol more stable than the chair conformer of axial 1-methyl-1-silacyclohexane. Axial 1-methyl-1-silacyclohexane is 3.53 and 4.67 kcal/mol more than its 1,4-twist and 2,5-twist conformers, and equatorial 1-methyl-1-silacyclohexane is 3.97 and 4.82 kcal/mol more stable than its 1,4-twist and 2,5-twist conformers. 1-Silabicyclo[2.2.1]heptane is 4.58 and 10.8 kcal/mol, respectively more stable than 2-silabicyclo[2.2.1]heptane and 7-silabicyclo[2.2.1]heptane. The influences of selectively replacing a CH2 group in a cycloalkane with a SiH2 group on the geometrical parameters, conformational properties, ring strain, and stereoelectronic hyperconjugative interactions are discussed. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

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