The cyclohexadienyl radicals (CHR) with both methyl and isopropyl substitutions are formed in the atmospheric oxidation of cyclohexadiene-type terpenes through hydrogen abstraction by OH radical. In this Letter, theoretical study is carried out on the reactions of O-2 with c-C6H7 and 2-methyl-5-isopropyl-, 2-isopropyl-5-methyl, and 1-isopropyl-4-methyl-CHRs under the atmospheric conditions. Calculations show that the reaction of c-C6H7 forms benzene and the reactions of three CHRs forms p-cymene + HO2 with almost unit yield. The reaction of c-C(6)H(7 )is much different to that of c-C6H6-OH. (C) 2018 Elsevier B.V. All rights reserved.