The Effect of Crowding in the Bay/Fjord Region on the Structure and Reactivities of Polycyclic Aromatic Hydrocarbons and their Metabolites: Quantum Mechanical Studies

Abstract

Polycyclic aromatic hydrocarbons with a crowded bay region, like benzo[c]phenanthrene, are nonplanar molecules with two helical structures. The bay region diol-epoxides of these PAHs retain the helical structure and therefore have twice as many possible conformations as the diol-epoxides of planar PAHs. Using quantum mechanical methods, it is shown that the conformation where the epoxide oxygen is near the distal ring is more stable than the conformation where it is away. The most stable syn- and anti- diastereomers for the diol-epoxides of five PAHs are computed. Computation of the electrostatic interaction between the epoxide group and the distal ring suggests that it provides the additional stabilization. Comparison is made between planar and nonplanar PAHs and between molecules where the crowding is due to a ring CH or a methyl group. These results suggest that the molecular electrostatic potential in the bay region can effect molecular reactivity.

Key words::

• Crowded bay region
• Quantum mechanics
• Electrostatic interaction