In path A, the initiation of the reaction, D can undergo a spin crossing event, in the proximity of the peroxyl radical generated previously, with an energy barrier of ΔG ‡ = 9.9 kcal/mol for D MECP , resulting in the formation of E (ΔG = -91.6 kcal/mol). Such hydroperoxide species are found to be stable for similar compounds. E then undergoes a scrambling reaction with an energy barrier of ΔG ‡ = 24.1 kcal/mol, through TS E-F , resulting in the final product, F1. In path A, the initial 18 Olabelled oxygen of the benzyl alcohol is retained.