Theoretical study on the methyl radical with chlorinated methyl radicals CH3-nCln (n = 1, 2, 3) and CCl2.

Radical–radical reactions involving chlorinated methyl radicals are particularly important in the mechanism of combustion of chlorinated hydrocarbons. Yet, they are usually difficult to study experimentally. In this paper, four chloride-related radical–radical reactions, i.e., CH₃+CH_3-nCl_n (n = 1, 2, 3) and CH₃+CCl₂, are theoretically studied for the first time by means of the Gaussian-3//B3LYP potential energy surface survey combined with the master equation study over a wide range of temperatures and pressures. Our calculated results show that the three CH₃+CH_3-nCl_n reactions can barrierlessly generate the former two kinetically allowed products P₁ H₂C&dbond;C(H)_3-nCl_n-1+HCl and P₂ CH₃CH_3-nCl_n-1+Cl with the very high predominance of P₁ over P₂. For the CH₃ reaction with the biradical CCl₂, which inevitably takes place during the CH₃+CCl₃ reaction and yet has never been studied experimentally or theoretically, H₂C&dbond;CCl₂+H and H₂C&dbond;C(H)Cl+Cl are predicted to be the respective major and minor products. The results are compared with the recent laser photolysis/photoionization mass spectroscopy study on the CH₃+CH_3-nCl_n (n = 1, 2, 3) reactions. The predicted rate constants and product branching ratios of the CH₃+CCl₂ reaction await future experimental verification. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [ABSTRACT FROM AUTHOR]