A theoretical study on the mechanism of oxidation of L-ascorbic acid
The oxidation of L-ascorbic acid (vitamin C) to dehydroascorbic acid is investigated by ab initio MO calculations. Their geometries together with intermediate species are optimized at the STO-3G level. The electron and spin densities are obtained with the 4-31G basis set. The five-membered (γ-lactone) ring is found to be planar during the oxidation process. Neutral and anion radicals are of the similar geometry but are of the different spin-density distribution. The stability of the ascorbate ion and the ascorbate anion radical is attributed to the ‘pseudo-aromaticity’ involved. The energy variation of the oxidation process of L-ascorbic acid is compared with that of triose reductone which is the simplest molecule having the same functional groups as the former compound.