CF_2ClC(O)OCH_2CH_3+OH的反应机理及动力学性质的理论研究

Mechanism and Kinetics of the Hydrogen-abstraction Reaction of CF_2ClC(O)OCH_2CH_3 with OH Radicals

利用双水平直接动力学方法,在MCG3-MPWB//M06-2X/aug-cc-pVDZ水平上研究了CF_2ClC(0)OCH_2CH_3+OH的微观反应机理.得到了反应物CF_2ClC(O)OCH_2CH_3的5种稳定构象(RCl^RC5),并对每一构象考察了发生在-CH_3-和-CH_2-基团上的所有可能氢提取反应通道.利用改进的变分过渡态理论(ICVT)结合小曲率隧道效应校正(SCT)计算了各反应通道的速率常数,分析了各构象反应位点选择性.结果表明,对于构象RCl和RC2,低温时氢提取反应主要发生在-CH_2-基团上;而对于构象RC3RC4和RC5,发生在-CH_3基团上的氢提取反应通道在整个温度区间内占绝对优势.根据Boltzmann配分函数计算总包反应速率常数,在298 K温度下计算的体系总包反应速率常数与实验值相符,进而给出200~1000 K温度范围内拟合了速率常数的三参数Arrhenius表达式:k_(overall)=5.45×10^(25)T^(4.54)exp(-685/T).

The mechanism of the hydrogen abstraction reaction of CF2CI（O） OCH2CH3 ＋ OH was studied theoretically via a dual-level direct dynamics method at the MCG3-MPWB//M06-2X/aug-ec--pVDZ level.Five stable conformers（RC1-RC5） of the reactant CF2C1（O） OCH2CH3 were located,and for each conformer,the possible H-abstraction channels from-CH3 and-CH2- groups were taken into account.The rate constants were calculated using the improved canonical variational transition-state theory（ICVT） with the small-curvature tunneling correction（SCT） and the selectivity of the reaction sites of CF2CI（O） OCH2CH3 was evaluated.The results show that for the conformers RC1 and RC2,the H-abstraction reactions mainly take place at the-CH2- group at low temperature,while for the conformers RC3,RC4 and RC5,the hydrogen abstraction from the-CH3group is the major channel in the whole considered temperature range.The overall rate constant is obtained by considering the weight factors of the five conformers calculated from the Boltzmannn distribution function.It is found,that the calculated k（overall） at 298 K is in good agreement with the available experimental data.The three parameter expression for the overall reaction within 200-1000 K is fitted to k（overall） =5.45 × 10^-25 T^4.54 exp（-685/T）.