The gamma-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-bromobenzene sulfonates were determined in 60% (v/v) aqueous ethanol (60E) and 97% (w/w) aqueous 2,2,2-trifluoroethanol (97Tw) at 50 degrees C. Tnt effects of aryl substituents at the silyl atom on these solvolyses were correlated with un exalted sigma degrees parameters, giving the rho values of -0.87 in 60E and -1.08 in 97Tw. This indicates that there exists a certain extent of positi ve charge on the gamma-silicon atom reflecting the delocalization of incipi ent carbocationic charge by participation of the Si-CY bond. The size of rh o values can be regarded as the effect of aryl ring on gamma-Si via percaud al interaction in the rate-determining step.