Radical cations of non-alternant systems as probes of the Shaik-Pross VB configuration mixing model

The valence bond configuration mixing (VBCM) model has been applied to predict the regioselectivity of radical cations of non-alternant systems, viz. dibenzofuran, dibenzothiophene, azulene, acenaphthylene and fluoranthene, toward reaction with nucleophiles. The reactivity factors of the VBCM model, the coefficients of the transfer orbital (TO) and spin densities of the lowest triplet state of each compound, have been calculated by means of high-level quantum chemical theory (CASPT2). The predictions have been compared with available experimental data. Since the expected regiochemical outcome of reactions of radical cations of this type with nucleophiles is distinctly different from that of the electrophilic reactions of the parent compounds, the approach offers a new way of testing the VBCM model. From a practical point of view, direct access to otherwise difficult to synthesize derivatives of these compounds via radical cation reactions should be an attractive possibility.