Acta Phys. -Chim. Sin. ›› 2012, Vol. 28 ›› Issue (12): 2824-2830.

• THEORETICAL AND COMPUTATIONAL CHEMISTRY •

### Accurate Calculation of the Reaction Barriers and Rate Constants of the Pyrolysis of Alkyl Radicals in the β Position Using the Isodesmic Reaction Method

WANG Bi-Yao2, TAN Ning-Xin2, YAO Qian1, LI Ze-Rong1, LI Xiang-Yuan2

1. 1 College of Chemistry, Sichuan University, Chengdu 610064, P. R. China;
2 College of Chemical Engineering, Sichuan University, Chengdu 610065, P. R. China
• Received:2012-07-31 Revised:2012-09-05 Published:2012-11-14
• Supported by:

The project was supported by the National Natural Science Foundation of China (20973118, 91016002)

Abstract:

The isodesmic reaction method is proposed for the accurate calculation of the reaction barriers and rate constants for an important class of reactions in the high-temperature combustion mechanism: the pyrolysis of alkyl radicals in the β position. The reaction barriers were calculated for a representative set of five reactions by two schemes: the first scheme is to calculate the reaction barriers directly from approximate ab initio calculations; and the second scheme is to correct the reaction barriers from the first scheme using the isodesmic reaction method. Ten different levels of ab initio calculations were used, and the absolute average maximum deviations of the reaction barriers by the isodesmic reaction method and direct ab initio calculations were 5.32 and 16.16 kJ·mol-1, respectively, indicating that the isodesmic reaction method does not significantly depend on the level of ab initio theory used. The rate constants of the three representative reactions in the temperature range of 500-2000 K were calculated by the isodesmic reaction method. The average and maximum values of kmax/kmin between the calculated and experimental values were 1.67 and 2.49, respectively. Therefore, the isodesmic reaction method is efficient and reliable for the calculation of the reaction barriers and rate constants of reactions in a class at a modest level of ab initio theory.

MSC2000:

• O643