Relative energies, stereoelectronic interactions, and conformational interconversion in silacycloalkanes

Abstract

AbstractStereoelectronic 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 CH2group in a cycloalkane with a SiH2group on the geometrical parameters, conformational properties, ring strain, and stereoelectronic hyperconjugative interactions are discussed. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004