THEORETICAL STUDY OF THE REGIOSELECTIVITY OF THE ADDITION OF THE TRIPLET OXYGEN ATOM TO UNSYMMETRICAL SUBSTITUTED ALKENES

A theoretical study of the reactivity and regioselectivity of the addition of the triplet oxygen atom O(P-3) to a series of unsymmetrical substituted alkenes has been performed at the PMP2/6-311++G(d,p) level of theory. Two reaction pathways, namely, the addition to the substituted carbon atom (alpha-site) and addition to the non-substituted carbon atom ( beta-site), have been studied. Our calculations show that the beta-addition products are kinetically more favored; whereas the alpha-addition products are found to be thermodynamically more stable. The regioselectivity (alpha vs. beta) of the addition of the O(P-3) to the carbon-carbon double bond is predicted by means of the relative energies of the localized transition states and also by the calculation of spin densities of the (3)pi pi* states of reactants and Fukui indices corresponding to the radical attack to alkenes. Our calculations are in good agreement with experimental outcomes.