The role of inductive,hyperconjugative and d-orbital effects in organosilicon compounds

The inductive hyperconjugative and d-orbital effects of PhSiMe₃, PhSiH₃, PhSiF₃ and of the respective carbon analogues have been investigated. Comparisons of calculated (CNDO/S method) and observed shifts for HOMO and LUMO levels indicate that all three effects have important roles in the organosilicon compounds. The relative importance of the effects depends on the compound; e.g. in PhSiMe₃ and PhSiH₃ hyperconjugation is the main effect, but in PhSiF₃ the effect of the d-orbitals is more important. The bathochromic shift in the UV transition of organosilicon compounds is not evident for the d-orbital effect.