Theoretical study on the epoxidation reaction mechanism between ethene, formamide and H₂O₂ was carried out using MP2 methods. The optimal structures of reactants, transition states, intermediates and products were located at the MP2/6-31G(d,p) level of theory. The reaction barriers were then calculated at the MP2/6-311＋＋G(d,p) level of theory. The calculation results show that the high reaction barriers exist for the pathways where no water molecule involves, whereas for the pathways in which a water molecule involves, the low reaction barriers were found because of the formation of the six-membered ring transition state structures, indicating that both the water molecule and the six-membered ring transition state structure play a very important role in the epoxidation reaction between ethene, formamide and H₂O₂.

Key words: epoxidation, four-membered ring transition state, six-membered ring transition state, water-assistance