Zhao Zeng-Xia, Liu Jing-Yao, Wang Li, Zhang Hong-Xing, Hou Chun-Yuan, Sun Chia-Chung
Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Changchun 130023, People's Republic of China.
J Phys Chem A. 2008 Sep 11;112(36):8455-63. doi: 10.1021/jp804010t. Epub 2008 Aug 16.
The hydrogen abstraction reactions C2H + CH3CN --> products (R1), C2H + CH3CH2CN --> products (R2), and C2H + CH3CH2CH2CN --> products (R3) have been investigated by dual-level generalized transition state theory. Optimized geometries and frequencies of all the stationary points and extra points along the minimum-energy path (MEP) are performed at the BH&H-LYP and MP2 methods with the 6-311G(d, p) basis set, and the energy profiles are further refined at the MC-QCISD level of theory. The rate constants are evaluated using canonical variational transition state theory (CVT) with a small-curvature tunneling correction (SCT) over a wide temperature range 104-2000 K. The calculated CVT/SCT rate constants are in good agreement with the available experimental values. Our calculations show that for reaction R2, the alpha-hydrogen abstraction channel and beta-hydrogen abstraction channel are competitive over the whole temperature range. For reaction R3, the gamma-hydrogen abstraction channel is preferred at lower temperatures, while the contribution of beta-hydrogen abstraction will become more significant with a temperature increase. The branching ratio to the alpha-hydrogen abstraction channel is found negligible over the whole temperature range.
采用双水平广义过渡态理论研究了氢提取反应C2H + CH3CN→产物（R1）、C2H + CH3CH2CN→产物（R2）和C2H + CH3CH2CH2CN→产物（R3）。使用BH&H-LYP和MP2方法以及6-311G(d, p)基组对所有驻点和沿最小能量路径（MEP）的额外点进行了几何结构优化和频率计算，并在MC-QCISD理论水平上进一步优化了能量分布。在104 - 2000 K的宽温度范围内，使用具有小曲率隧道效应校正（SCT）的正则变分过渡态理论（CVT）评估了速率常数。计算得到的CVT/SCT速率常数与现有的实验值吻合良好。我们的计算表明，对于反应R2，在整个温度范围内，α-氢提取通道和β-氢提取通道相互竞争。对于反应R3，在较低温度下，γ-氢提取通道占优，而随着温度升高，β-氢提取的贡献将变得更加显著。发现在整个温度范围内，α-氢提取通道的分支比可忽略不计。
