The γ-Silicon Effect. II. The Substituent Effect on the Solvolysis of 3-(Aryldimethylsilyl)-2,2-dimethylpropyl p-Bromobenzenesulfonates

Solvolysis rates of 3-(aryldimethylsilyl)-2,2-dimethylpropyl p-bromobenzenesulfonates were determined in 60% (v/v) aqueous ethanol (60E) and 97% (w/w) aqueous 2,2,2-trifluoroethanol (97Tw) at 50 °C. The effects of aryl substituents at the silyl atom on these solvolyses were correlated with unexalted σ° parameters, giving the ρ values of −0.87 in 60E and −1.08 in 97Tw. This indicates that there exists a certain extent of positive charge on the γ-silicon atom reflecting the delocalization of incipient carbocationic charge by participation of the Si–Cγ bond. The size of ρ values can be regarded as the effect of aryl ring on γ-Si via percaudal interaction in the rate-determining step.