Investigations on Kinetics for the Reaction Class of Hydrogen Abstractions from Substituted Cyclopentane by Hydroxyl Radical

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 cyclopentane. 16 Hydrogen abstraction reactions from the side chain and 10 reactions with hydrogen abstraction from the alpha-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 alpha-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.