关键词: 反应类等键反应方法, 反应势垒, 速率常数, 过氧烷基分子内氢迁移反应

Abstract:

Intramolecular hydrogen migration in alkylperoxy reactions is one of the most important reaction classes in hydrocarbon combustion at low temperatures. In this study, the kinetic parameters for reactions in this class were calculated using the isodesmic reaction method. The geometries for all the reactants, transition states, and products were optimized at the B3LYP/6-311+G(d,p) level. A criterion based on conservation of the reaction-center geometry of the transition state was proposed for the reaction class, and the intramolecular hydrogen migration reactions studied were divided into four classes, i.e., (1,3), (1,4), (1,5), and (1,n) (n=6, 7, 8) hydrogen migration. The simplest reaction system for each reaction class was defined as the principal reaction; the approximate single-point energies were obtained at the low level of B3LYP/6-311+G(d,p) and accurate single-point energies were obtained at the high level of CBS-QB3. The other reactions in this class were chosen as the target reactions and the approximate single-point energies were obtained at the B3LYP/6- 311+G(d,p) level. The energy barriers and rate constants of these target reactions were corrected using the isodesmic reaction method. The results showed that accurate energy barriers and rate constants for the reactions of large molecules can be obtained by a relatively low level method using the isodesmic reaction method. In this study, classification of the basic isodesmic reaction showed the essential features of the reaction classes. The present work provides accurate kinetic parameters for modeling intramolecular hydrogen migration reactions of hydrocarbons at low temperatures.

Key words: Isodesmic reaction method for the reaction class, Reaction barrier, Rate constant, Intramolecular hydrogen migration reactions of alkylperoxy radicals