Protonation of Phenyl(trimethylsilyl)acetylene: A Surprisingly Weak Stabilization of a Carbocation by a β‐Trimethylsilyl Group

The protodesilylation of the title compound 1 [Eq. (a)] proceeds via the vinyl cation 2 , whose stabilization by the β‐trimethylsilyl group is much smaller than expected. The comparison of the rate of protonation of 1 and that of phenylacetylene gives a small β‐silyl stabilizing effect (ΔΔ G † = 3.4 kcal mol −1 ). This surprising result is explained by insufficient hyperconjugation.