Calculated reactivities of potentially carcinogenic intermediates of the cyclopenta-fused isomers of benz[a]anthracene.

Delocalization energies have been calculated for carbocations formed from several epoxide intermediates of the cyclopenta-fused isomers of benz[a]anthracene. Except for the epoxides of benz[l]aceanthrylene, the largest calculated delocalization energies associated with the other benzaceanthrylenes result from ring-opening of the epoxide on the cyclopenta-ring yielding an alpha' type carbocation. Benz[l]aceanthrylene exhibits special behavior resulting from steric crowding in the bay-region of the molecule. For this molecule the calculated ease of epoxide ring opening is essentially the same for the bay-region epoxide and for the epoxide on the five-membered ring. Relative values of delocalization energy should provide an important index for ranking the reactivity of metabolites of the benzaceanthrylenes and benzacephenanthrylene that are potentially involved in the initiation of mutagenesis/carcinogenesis.