1,3-环己二烯与丙烯反应exo和endo机理的理论研究

Theoretical Study on the exo and endo Reaction Mechanisms of 1,3-Cyclohexadiene with Propylene

采用从头算方法在3-21G基组上研究了1,3-环己二烯与丙烯生成exo和endo产物的反应机理.该反应生成exo和endo产物各存在三条反应途径,其中两条为分步途径,一条为协同途径.经计算研究表明:1,3-环己二烯与丙烯生成exo和endo产物的有利途径为经过一个双自由基中间体的分步过程,由丙烯端位碳原子先进攻的分步过程最为容易.对应于该过程,生成exo和endo产物的反应速控步骤的位垒值分别为80.69kJ/mol和75.58kJ/mol.表明生成endo产物的反应比生成exo产物的反应略为有利.

The exo and endo reaction mechanisms of 1,3 - cyclohexadiene with propylene have been comprehensively studied by using ab initio method at 3 - 21G level. The exo and endo products of the reaction can be separately formed through three reaction paths. Two of them are stepwise processes. The third is concerted one. The theoretical study results show that the favorite exo and endo reaction paths of 1,3 - cyclohexadiene with propylene are the stepwise processes via biradical intermediates, in which the terminal carbon of propylene attacks 1,3 -cyclohexadiene at the first step. Corresponding to these stepwise paths, the activation barriers for the rate determining steps to form exo and endo products are 80. 69kJ/mol and 75. 58kJ/mol, respectively. Therefore, the reaction forming endo product is slightly easier than that of exo one.