About possibility of the triplet mechanism of the Meerwein reaction

Calculations of 25 unsaturated compounds in the ground singlet and excited triplet states have been carried out using density functional theory (DFT) method at B3LYP/6-31G(d, p) level of theory. Their oxidized radical cation forms have also been calculated. Correlations between the yields of the Meerwein reaction products and the corresponding lowest unoccupied molecular orbital (LUMO) energies as well as the triplet excitation energies have been established. Activation of the unsaturated compounds via the triplet excited state formation has been shown as induced by exchange interaction either with paramagnetic aryl radical or with paramagnetic aryl triplet cation. Two competing routes of the Meerwein reaction have been offered depending on the presence of the catalyst. In the absence of redox (catalytic) systems the reaction is considered to be a direct ion addition. Spin-orbit coupling effects enabling the singlet-triplet transition in the aryl cations are also discussed.