γ-Silicon Stabilization of Carbonium Ions in Solvolysis. 2. Solvolysis of 4-(Trimethylsilyl)-2-butyl p-Bromobenzenesulfonates

Article abstract of DOI:10.1021/ja00237a027

The solvolysis of 4-(trimethylsilyl)-2-butyl p-bromobenzenesulfonate produces racemic substitution products and a minor amount of methylcyclopropane at a rate which is several-fold faster than the solvolysis of its carbon analogue; polarimetric and conductometric rates are not significantly different.Added LiClO4, KOH, KOBs, and LiOBs produced normal salt effects on the polarimetric rate; b values varied from 0.2 to 130, depending on the nature of the salt and solvent.The deuterium isotope rate effects vary somewhat with solvent as follows: α-d, 1.12-1.15; β-d₃, 1.115-1.16; β-d₂, 0.975-1.07.It is concluded that the γ-silyl group promotes the solvolysis and stabilizes the intermediate carbonium ion.The "W" and "sickle" conformations of the transition states for the formation and/or reaction of the carbonium ion intermediate have approximately equal energies.