Calculations Related to the Reactivity of Polycyclic Aromatic Hydrocarbon Episulfides

Abstract

The opening reaction of S-protonated polycyclic aromatic hydrocarbon episulfides has been evaluated by means of ab initio, density-functional, and semiempirical calculations. Episulfides are predicted to open more easily than the corresponding O-protonated derivatives, epoxides, and diol epoxides. On the other hand, diol episulfides would present the slowest rate for opening, the syn isomers being expected to be more reactive than the anti isomers. Bay-region and methyl-substituted bay-region compounds were found to open more readily among the sulfur derivatives, following the same reactivity pattern as the oxygen analogs. The exothermicity of the opening process correlated with the charge delocalization in the resulting carbocation. This reaction step is very important in the carcinogenic pathway of the epoxide analogs. Thus, according to the present calculations, episulfides could possibly exert carcinogenic activity.