FORS MCSCF STUDY ON NITRENOPHENYLMETHYLENE (C6H4CHN)

Electronic structure calculations for the ortho, meta, and para isomer s of nitrenophenylmethylene (C6H4-CHN) are carried out by using the fu ll-optimized-reaction-space (FORS) multiconfiguration self-consistent- field (MCSCF) method with the STO-3G basis set. The ortho isomer is pr edicted to possess a singlet ground state with a bond-alternated struc ture. However, since the energy barrier for the isomerization reaction of the ortho structure to a bicyclic one (benzoazacyclobutene or benz [b]azete) is less than 10 kcal/mol, the ortho isomer is considered to have a relatively short lifetime and hence to exist in the stable bicy clic form. The para isomer also has a singlet ground state with a bond -alternated structure, but it may easily react with molecular oxygen, as suggested experimentally, because the lowest tripler state is very close in energy to the singlet ground state. In marked contrast, the m eta isomer has a quintet ground state, and this aspect is well reflect ed in the bonding, which shows no appreciable pi conjugation between a benzene nucleus and two radical substituents.