Theoretical dynamic studies on the reactions of CH₃C(O)CH₃₋nCln (n = 0-3) with the chlorine atom

• Published in: Journal of computational chemistry 2008-04, Vol.29 (5), p.809-819
• Main Authors: Ji, Yue-meng, Zhao, Xiao-lei, Liu, Jing-yao, Wang, Ying, Li, Ze-sheng
• Format: Article
• Language: English
• Subjects: ab initio calculations; rate constant; reaction dynamics
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.20825

The theoretical investigations were performed on the reaction mechanisms for the title reactions CH₃C(O)CH₃ + Cl [rightward arrow] products (R1), CH₃C(O)CH₂Cl + Cl [rightward arrow] products (R2), CH₃C(O)CHCl₂ + Cl [rightward arrow] products (R3), and CH₃C(O)CCl₃ + Cl [rightward arrow] 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 (---CH₃₋nCln) 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 addition-elimination 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.