Theoretical study of oxocyclohexadienylidene isomers: Electronic structures and molecular properties

The molecular properties and electronic structures for three isomers of oxocyclohexadienylidene were investigated using multiconfiguration SCF (MCSCF) wave functions. The ground electronic states of the ortho and para isomers are the open shell triplet, whereas the meta isomer has a singlet ground state with significant open shell character. The structural features of the ground states of all three isomers are close to the" quinoid type structure. Several molecular properties such as the electron spin density, electron affinity (EA), acidity and bond dissociation energy for the three isomers and/or their corresponding radicals are also considered and are compared with experimental values. In particular, the MCSCF(8,8)/6-31+G* electron spin densities for both ortho and para isomers are very close to the experimental values of the phenoxyl radical.