The γ-silicon effect. II. The substituent effect on the solvolysis of 3-(aryldimethylsilyl)-2,2-dimethylpropyl p-bromobenzenesulfonates

Article abstract of DOI:10.1246/bcsj.72.1043

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.