Quantum mechanical studies of the structure and reactivities of the diol epoxides of benzo[c]phenanthrene.

Benzo[c]phenanthrene has a crowded bay region that has been called a fjord region. As a result of the interaction between the atoms across the fjord region, it is a nonplanar molecule with a significant barrier between two helical structures. The crowding in the fjord region also affects the three-dimensional structure of the fjord region diol epoxide. Quantum mechanical studies have been performed to determine the structure and reactivities of the fjord region diol epoxides. Eight local minimum energy three-dimensional structures have been found for the trans diol of 1,2,3,4-tetrahydro-3,4-dihydroxybenzo[c]phenanthrene 1,2-epoxide. They can be characterized by three dichotomies: one between syn and anti, one between quasidiaxial and quasidiequatorial, and the third that depends on nonplanarity of the parent polycyclic aromatic hydrocarbon due to interactions in the crowded bay region, that we have named "in" and "out" based on the position of the epoxide oxygen relative to the distal ring. The structures with the epoxide oxygen on the same side of the saturated ring as the distal ring (in-) are more stable than the structures where the epoxide is on the opposite side (out-). The calculated lowest energy syn and anti structures for the diol epoxide of benzo[c]-phenanthrene are both in-quasidiequatorial, in agreement with experiment. Analysis of the results indicates that the electrostatic interaction across the fjord region could be responsible for the increased stability of the syn-in-quasidiequatorial structure compared to the syn-in-quasidiaxial structure and the stability of the in- structures in general when compared to the out- structures.(ABSTRACT TRUNCATED AT 250 WORDS)