Kinetic mechanism of the hydrogen abstraction reactions of the chlorine atoms with CH3CF2Cl and CH3CFCl2: A dual level direct dynamics study

• Published in: Journal of computational chemistry 2007-04, Vol.28 (5), p.975-983
• Main Authors: Ji, Yue-meng, Zhao, Xiao-lei, Li, Ze-sheng, Liu, Jing-yao
• Format: Article
• Language: English
• Subjects: ab initio calculations; computer chemistry; gas-phase reactions; kinetics
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.20665

The mechanisms of the reactions: CH3CFCl2 + Cl (R1) and CH3CF2Cl + Cl (R2) are studied over a wide temperature range (200–3000 K) using the dual‐level direct dynamics method. The minimum energy path calculation is carried out at the MP2/6‐311G(d,p) and B3LYP/6‐311G(d,p) levels, and energetic information is further refined by the G3(MP2) theory. The H‐ion from the out‐of‐plane for (R1) is the major reaction channel, while the in‐plane H‐ion is the predominant route of (R2). The canonical variational transition‐state theory (CVT) with the small‐curvature tunneling (SCT) correction method is used to calculate the rate constants. Using group‐balanced isodesmic reactions and hydrogenation reactions as working chemical reactions, the standard enthalpies of formation for CH3CFCl2, CH3CF2Cl, CH2CFCl2, and CH2CF2Cl are evaluated at the CCSD(T)/6‐311 + G(3df,2p)//MP2/6‐311G(d,p) level of theory. The results indicate that the substitution of fluorine atom for the chlorine atom leads to a decrease in the CH bond reactivity with a small increase in reaction enthalpies. Also, for all reaction pathways the variational effect is small and the SCT effect is only important in the lower temperature range on the rate constants. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007