烷烃与羟基自由基反应速率常数的估算

根据烷烃分子中碳氢键离解能与烷基Ri的极化效应指数(PEI)的关系,由PEI表达烷烃C-H键与羟基自由基反应的活化能E;用烷基Ri的拓扑立体效应指数(TSEI)定量相关阿仑尼乌斯公式中的指数前因子A.研究表明PEI、TSEI和温度T三参数可以定量关联羟基自由基与烷烃中伯、仲、叔碳氢键反应的活性.所得方程可以准确地区分不同C-H键的活性.结合烷基Ri的PEI和TSEI参数用于预测不同温度下烷烃、环烷烃与羟基自由基反应的绝对速率常数和相对速率常数,预测值与实验值一致.

Evaluation of Rate Constants in the Reactions of Hydroxyl Radical with Alkanes

Activation energy of hydroxyl radical OH reacting with alkanes was estimated from the quantitative relation between the bond dissociation energy (BDE) of R_i-H and the polarizability effect index (PEI) of alkyl radical R_i. Preexponential factor A in Arrhenius expression quantitatively was related to the topological steric effect index (TSEI) of alkyl radical R_i. The research results show that three parameters, PEI, TSEI and temperature T, can be used to quantify the activity of hydroxyl radical reacting with primary, secondary and tertiary carbon-hydrogen bonds in alkane. The expression can accuratly evaluate the activity of C-H bonds. Moreover, the PEI and TSEI of alkyl radical R_i can be correlated quantitatively with the reaction absolute and relative rates of alkanes and cyclanes with hydroxyl radicals at various temperatures. The predicted rate constants are in good agreement with the experimental ones.