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 f iord region. As a result of the interaction between the atoms across t he 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 epox ide. Quantum mechanical studies have been performed to determine the s tructure and reactivities of the fjord region dial epoxides. Eight loc al minimum energy three-dimensional structures have been found for the trans diol of 2,3,4-tetrahydro-3,4-dihydroxybenzo[c]phenanthrene 1,2- epoxide. They can be characterized by three dichotomies: one between s yn and anti, one between quasidiaxial and quasidiequatorial, and the t hird that depends on nonplanarity of the parent polycyclic aromatic hy drocarbon due to interactions in the crowded bay region, that we have named ''in'' and ''out'' based on the position of the epoxide oxygen r elative 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 di ol epoxide of benzo[c]phenanthrene are both in-quasidiequatorial, in a greement with experiment. Analysis of the results indicates that the e lectrostatic interaction across the fjord region could be responsible far 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. These calculations suggests that the electrostatic contribution of the dist al ring in the fjord/bay region may play a part in the interaction wit h nucleophiles.