Laboratorium voor Chemische Technologie, Universiteit Gent, Krijgslaan 281 S5, B-9000 Gent, Belgium.
Phys Chem Chem Phys. 2010 Feb 14;12(6):1278-98. doi: 10.1039/b919479g. Epub 2009 Dec 14.
Resonance stabilization of the transition state is one of the key factors in modeling the kinetics of hydrogen abstraction reactions between hydrocarbons. A group additive model is developed which allows the prediction of rate coefficients for bimolecular hydrogen abstraction reactions over a broad range of hydrocarbons and hydrocarbon radicals between 300 and 1300 K. Group additive values for 50 groups are determined from rate coefficients determined using the high level CBS-QB3 ab initio method, corrected for tunneling and the hindered internal rotation around the transitional bond. Resonance and hyperconjugative stabilization of the transition state is accounted for by introducing 4 corrections based on the structure of the reactive moiety of the transition state. The corrections, fitted to a set of 28 reactions, are temperature-independent and reduce the mean absolute deviation on E(a) to 0.7 kJ mol(-1) and to 0.05 for log A. Tunneling contributions are accounted for by using a fourth order polynomial in the activation energy. Final validation for 19 reactions yields a mean factor of deviation between group additive prediction and ab initio calculation of 2.4 at 300 K and 1.8 at 1000 K. In comparison with 6 experimental rate coefficients (600-719 K), the mean factor of deviation is less than 3.
共振稳定过渡态是建模烃类之间氢提取反应动力学的关键因素之一。本文开发了一种基团加和模型，能够预测在 300 到 1300 K 温度范围内，广泛的烃类和烃自由基之间双分子氢提取反应的速率常数。通过使用高精度 CBS-QB3 从头算方法确定的速率常数，并经过隧道效应和过渡键受阻内旋转校正，确定了 50 个基团的基团加和值。通过引入基于过渡态反应部分结构的 4 个校正项来考虑过渡态的共振和超共轭稳定。这些校正项拟合了 28 个反应，与温度无关，将 E(a)的平均绝对偏差降低到 0.7 kJ mol(-1)，log A 的平均绝对偏差降低到 0.05。采用激活能的四阶多项式来考虑隧道效应贡献。对 19 个反应进行最终验证，得到在 300 K 时基团加和预测与从头算计算之间的平均偏差因子为 2.4，在 1000 K 时为 1.8。与 6 个实验速率常数（600-719 K）相比，平均偏差因子小于 3。
