Molecular oxygen is a triplet species in its ground state. Although thermochemically not very stable, it poses significant kinetic barriers for reaction. The oxidation of the thiol moiety with this oxidant leads to a barrier of about 30 kcal/mol (pathway (c) in Figure ) and thus leaves little chance for the reaction to proceed when compared to the low kinetic barrier in the backward direction. On the other hand, the reaction intermediate in this mechanism is observed to be endergonic, by about 25.0 kcal/mol, and so it can be concluded that the oxidation with triplet oxygen is not a favoured process.