Theoretical study of the reaction mechanism of ethynyl radical with benzene and related reactions on the C8H7 potential energy surface

Ab initio G3(MP2,CC)//B3LYP/6-311G∗∗ calculations have been performed to investigate the C2H + C6H6 and C4H3 + C4H4 reactions on the C8H7 potential energy surface. The results demonstrate that C2H reacts with benzene without a barrier and then the C6H6(C2H) adduct produced loses atomic hydrogen to form phenylacetylene with overall reaction exothermicity of 28.4 kcal/mol. The reaction can be a major source of phenylacetylene under low-temperature conditions of Titan’s atmosphere. The reactions of vinylacetylene and butatriene with i-C4H3, producing phenylacetylene, pentalene, or benzocyclobutene, are predicted to be unlikely at low temperatures because of significant barriers but may be important in combustion flames.