Ascorbic acid: The chemistry underlying its antioxidant properties.

Ascorbic acid (vitamin C) is an unusual antioxidant in that it donates a single reducing equivalent, and the radical it forms, monodehydroascorbate, reacts preferentially with radicals instead of with non-radical compounds. This happens because removal of an electron from monodehydroascorbate would create a tricarbonyl structure that is energetically unfavored. Instead of forming this structure, ascorbic acid oxidizes only to monodehydroascorbate, and monodehydroascorbate reacts with other radicals, oxidizing by mechanisms that may circumvent formation of this unfavored structure.