Abstract

Hückel molecular orbital calculations have been performed on a series of polycyclic aromatic hydrocarbons (PAH) to obtain bond localization energies and π-electron stabilization energies for the reaction sequence through which the "bay region" diol epoxide is formed. These calculations suggest that carcinogenic PAH and non-carcinogenic PAH may exhibit different behavior at three points in the sequence. The highest localization energies for formation of the initial epoxide are exhibited exclusively by a block of non-carcinogenic PAH, suggesting that they may form only minimal amounts of the initial dihydrodiol. Of the remaining PAH, the carcinogens generally exhibit greater π-electron stabilization than do non-carcinogens following opening of both the initial epoxide and the diol epoxide rings, possibly indicating more facile production of the initial dihydrodiol and of the final biomolecule adduct. The relative potencies of the twelve carcinogenic PAH considered, as measured by the Iball Index, can be satisfactorily reproduced (correlation coefficient = 0.90) through an equation combining indices for formation of the initial epoxide and for π-electron stabilization of its ring-opened cation.