Theoretical dynamic studies on the reactions of CH₃C(O)CH _3-nCl_n (n = 0-3) with the chlorine atom

The theoretical investigations were performed on the reaction mechanisms for the title reactions CH₃C(O)CH₃ + Cl → products (R1), CH₃C(O)CH₂Cl + Cl → products (R2), CH ₃C(O)CHCl₂ + Cl → products (R3), and CH ₃C(O)CCl₃ + Cl → products (R4) by ab initio direct dynamics approach. Two different reaction channels have been found: abstract of the H atom from methyl (-CH₃) group or chloromethyl (-CH _3-n,C1_n) group of chloroacetone and addition of a Cl atom to the carbon atom of the carbonyl group of chloroacetone followed by methyl or chloromethyl eliminations. Because of the higher potential energy barrier, the contribution of additionelimination reaction pathway to the total rate constants is very small and thus this pathway is insignificant in atmospheric conditions. The rate constants for the H-abstraction reaction channels are evaluated by using canonical variational transition state theory incorporating with the small-curvature tunneling correction. Theoretical overall rate constants are in good agreement with the available experimental values and decrease in the order of k₁ > k₂ > k₃ > k₄. The results indicate that for halogenated acetones the substitution of halogen atom (F or Cl) leads to the decrease in the C-H bond reactivity and more decrease of reactivity is caused by F-substitution.