A theoretical study of benzene protonation

The structures of σ and π complexes of C<inf>6</inf>H <inf>7</inf>⁺ are examined by both MINDO/3 and ab initio methods. The crucial role played by full optimization of the geometry is established. From the examination of the potential energy surface it appears that there are two different channels for benzene protonation, one through the π complex, and the other leading directly to the σ complex. The π complex may be considered to be a transition state for the intramolecular isomerization of the σ complex.