Molecular orbital calculations on the 2-phenylethyl .far. phenonium cation transformation

The reaction coordinate for the transformation, classical 2-phenylethyl → phenonium cation, has been mapped using CNDO/2 calculations. That the results of such calculations must be quantitatively grossly incorrect was shown by the results of similar calculations for the corresponding radical species. We show that CNDO/2 has a built-in bias for three-membered ring formation, at least for the Pople and Wiberg parametrizations. Extended Hückel calculations on the same problem give results which are the qualitative inverse of those of CNDO. However, known experimental data demonstrate that the EHT results are also quantitatively incorrect. Thus neither semiempirical calculation gives results which can be trusted.