Carcinogenicity of methylated benzo(a)pyrene: Calculated ease of formation of the bay-region carbonium ion

The relative ease of bay-region carbonium ion formation is calculated for methyl group substitutions that are not on the angular metabolized benzo-ring of the highly reactive bay-region diol-epoxide of benzo(a)pyrene. Methyl group substitution in the bay-region, at position 11, is shown to yield the most highly reactive monomethyl isomer. The least reactive group of isomers involves substitutions at positions 2, 5 and 6. Substitutions at positions 1, 3, 4 and 12 are found to yield calculated reactivities that are intermediate to those found for the least reactive group and that found for the most reactive substitution. The calculated ranking of reactivities closely parallels the results of a recent experimental study by Iyer et al. The results of calculation for dimethyl substitutions are also presented.