Computational study of the addition of molecular oxygen to benzene

The first step of the attack of the oxygen molecule, in its ground state, on the phenyl ring, in the gas phase, has been studied using SCF ab initio, BECKE3LYP DFT and AM1 and PM3 semiempirical calculations. This attack follows several stages: fixation of the oxygen molecule in the para position, then its dissociation followed by a two-step migration of hydrogen atoms, leading finally to hydroquinone. The potential curves obtained by DFT and SCF calculations are similar; the same stationary points are observed in both methods. However, the SCF energy barriers are overestimated by a factor greater than 30%. The semiempirical computations reproduce approximately some features of the non-empirical results. (C) 1997 Elsevier Science B.V.