Figure 2. Keto-enol tautomerization in L-Ascorbic acid

The predominant structure of AscA is shown in Figure 1; however, AscA can exist as a variety of keto-enol tautomers, i.e., isomers resulting from the migration of a proton accompanied by inter- conversion of a C=C or C=O double bond with an adjacent C–O or C–C bond, respectively (Figure 2).