Energetics of hindered rotation in disilane are analyzed and compared to ethane. In disilane weakened (rotationally governed) hyperconjugative interactions, paramount in controlling the ethane barrier, leave the nonrotational part of the torsional coordinate as the primary contribution to disilane barrier energetics. In this regard, the 0.012 Å Si-Si bond lengthening that accompanies rotation is found to account for most of the 1.0 kcal/mol barrier. Although both the Si-Si bond expansion in disilane and the 0.014 Å C-C bond expansion in ethane are nearly the same, the mechanisms for these expansions are found to be different. Unlike in ethane, where the expansion is largely due to the hyperconjugation decrease in the eclipsed conformer, in disilane it is almost entirely due to electrostatic repulsion between Si-H bonds in the two silyl groups.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry