烷基环戊烷被羟基自由基夺氢反应类的动力学研究

摘要

基于燃烧详细反应机理构建的需要,采用反应类过渡态理论(RC-TST)研究了OH自由基夺取烷基环戊烷环上和侧链上氢原子的动力学.在考察侧链氢提取反应类的16个代表反应的基础上,本工作首次将该方法推广到环上α氢提取反应类的10个代表反应的研究,分别建立了两类反应的线性自由能(LER)关系式.计算结果表明,采用RC-TST/LER方法预测的这两类反应的速率常数与直接应用TST/Eckart方法得到的结果接近,说明RC-TST/LER方法对预测这两类反应的速率常数非常有效,且节约了大量计算成本.而且,无论是侧链还是五元环,OH·夺取叔碳上的氢原子最易发生.%In order for the development of the detailed combustion mechanisms, this work applies the reaction class transition state theory (RC-TST) to predict kinetics parameters for hydrogen abstraction reactions from the substituted cyclopen-tane. 16 Hydrogen abstraction reactions from the side chain and 10 reactions with hydrogen abstraction from the a-carbon atom on the ring have been investigated with RC-TST/LER method. The corresponding linear energy relationship (LER) has also been established. All the geometries of reactants, transition states, and products are optimized at BH&HLYP level of theory with the basis set of cc-pVDZ, and the electronic energy calculation and frequency analyses are also carried out at the same level of theory. Accordingly, the RC-TST factors and LER are derived based on the calculations. For the reference reaction, the minimum energy path of the potential energy surface is obtained at the BH&HLYP/cc-pVDZ level. In order to get the more precise rate constants of the reference reaction, the single-point energies of the selected points along the minimum energy path are calculated at the CCSD(T)/cc-pVDZ level. In the RC-TST/LER method, the other rate constants in this class can be derived from the reference reaction and the RC-TST factors. Our analyses indicate that the rate constants for selected reactions predicted by the RC-TST/LER are in good agreement with those calculated with TST/Eckart method. For the hydrogen abstraction reactions from the side chain and the a-carbon atom on the ring, the maximum error between the two methods is less than 73% and 88%, respectively. Moreover, it is found that the error decreases with the increasing of the temperature. Therefore, the RC-TST/LER method seems to be quite efficient to estimate the rate constants for a large number of reactions in this class and to save a lot of computational resource. In addition, for the two types of reaction classes, the hydrogen at the tertiary carbon can be easily abstracted by hydroxyl radical.