Reaction of Methylbenzanthracenes and Pyridine by One-Electron Oxidation. A Model for Metabolic Activation and Binding of Carcinogenic Aromatic Hydrocarbons

A simple procedure for generation and trapping of polycyclic aromatic hydrocarbon radical cations in homogeneous solutions of pyridine and iodine is described. Radical cations of benz[a]anthracene and its alkyl derivatives are trapped by nucleophilic attack of pyridine on the aromatic nucleus in the order C-7 > C-12 > C-5. When positions 7 or 7 and 12 are blocked by a methyl group, pyridine substitution on the alkyl group competes with ring substitution. Mechanisms for the two types of substitution are proposed and trapping specificity is discussed in terms of charge density and steric factors in the radical ions.