Rearrangements involving the phenonium ion: a theoretical investigation.

Rearrangements involving the phenonium ion were investigated by means of a B3LYP/6-311G(d,p) study in which the effect of solvent has been incorporated by using a PCM solvation model. A rationalization of the whole set of experimental facts reported both in the gas phase and in solution was possible thanks to the characterization of protonated benzocyclobutene as a minimum energy structure and, particularly, to the important preferential stabilization in solution of the TS for the isomerization of the phenonium ion to the alpha-methylbenzyl ion, which reduces the Gibbs energy barrier of 26.6 kcal/mol for this process in the gas phase to a more accessible one of 18.7 kcal/mol in solution.