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 (ΔΔG† = 3.4 kcal mol−1). This surprising result is explained by insufficient hyperconjugation.