Benzene Oxidation in the Troposphere. Theoretical Investigation on the Possible Competition of Three Postulated Reaction Channels

Three different attacks of 3 Σ g O 2 on the hydroxycyclohexadienyl radical intermediate I (generated from the reaction of OH • with benzene) have been studied by Density Functional Theory. Both abstraction by O 2 of the hydrogen gem to OH in I (affording phenol) and O 2 addition to the π-delocalized system of I (producing a hydroxycyclohexadienyl peroxyl radical intermediate) appear to be very viable, with Δ H ⧧ = 3−4 kcal mol - 1 . The former reaction is exothermic by 27 kcal mol - 1, the latter only by 1 kcal mol - 1 . In contrast, a recently repropounded pathway, which would lead to benzene oxide/oxepin, via hydrogen abstraction from the hydroxyl in I operated by O 2, appears not to be competitive, showing a significantly higher barrier (Δ H ⧧ = 32 kcal mol - 1 ). Benzene oxide and oxepin are estimated to lie 21 and 19 kcal mol - 1 above I, respectively.