Theory and application of photoelectron spectroscopy : V. The nature of bonding in vinyl- and allylsilanes: The effects of σ-π (hyperconjugation) and pπ- dπ conjugation in these compounds

Abstract

The photoelectron spectra of vinylsilane (II), trimethylvinylsilane (IV), and trimethylallylsilane (VI) have been recorded along with those of the corresponding carbon compounds propene (I), 3,3-dimethyl-1-butene (III), and 4,4-dimethyl-1-pentene (V). Comparison reveals a close parallel between the highest occupied MO's in the silicon compounds and those in the carbon compounds. The electronic structure of both series of compounds is discussed in terms of bond energies (CH, CC, SiH, SiC bonds), of hyperconjugative interaction of these bonds with the ethylene π MO, and of p π- d π conjugation between the d π AO's on the silicon atom and the adjacent π MO. The importance of p π- d π bonding in vinylsilanes (involving the SiC bonds) is clearly established from valence electron calculations (MINDO/1 and CNDO/2).