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.

Key words: REACTION MECHANISM, PROPENE, AB INITIO CALCULATION, CYCLOHEXADIENE