A reinvestigation of the mechanism of epoxidation of alkenes by peroxy acids. A CASSCF and UQCISD study

The transition state structure for the reaction of epoxidation of ethylene with peroxyformic acid is investigated at the CASSCF and UQCISD levels of theory. Both methods yield a highly unsymmetrical oxygen-addition transition state which has a diradical character. The value of the activation barrier calculated at the MCQDPT2(12,12)/6-311++G(d,p)//CASSCF(12,12)/6-311++G(d,p) correlated level (18.3 kcal/mol) is within the range of experimentally measured values. The predicted values of KIEs are in good agreement with the experimental data.