ULTRAVIOLET PHOTOELECTRON STUDIES OF POLYCYCLIC AROMATIC-HYDROCARBONS - GROUND-STATE ELECTRONIC-STRUCTURE OF ARYLOXIRANES AND METABOLITES OF BENZO[A]PYRENE

UV photoelectron spectroscopy was employed to study the ground-state electronic structure of a series of aryloxiranes, of phenanthrene 9,10-oxide, and of two metabolites of benzo[a]pyrene including the highly carcinogenic diol epoxide, trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene. The photoelectron spectra of the aryloxiranes and the benzo[a]pyrene metabolites were assigned by comparison with the spectra of the parent polycyclic arenes and ethylene oxide. Spectral assignments were confirmed by comparison of experimental ionization potentials with energy levels predicted by semiempirical molecular orbital calculations based on the CNDO/S 3 method. The photoelectron spectrum of the diol epoxide of benzo[a]pyrene is approximated by the combined spectra of pyrene and ethylene oxide. However, electronic coupling of the saturated six-membered ring with its substituent groups to the π system of the pyrene moiety does occur. In the diol epoxide of benzo[a]pyrene all five of the uppermost π orbitals are destabilized compared to those in pyrene. This destabilization, which in the second highest occupied π orbital has a magnitude greater than 0.4 eV, is expected to aid in the stabilization of intermediates associated with biologically important electrophilic alkylation reactions. © 1979 American Chemical Society.