Ascorbic Acid (Vitamin C) Is a Diprotic Acid with Two

Essay

Ascorbic acid (Vitamin C) is a diprotic acid with two pK_a values; pK_a1 = 4.2 and pK_a2 = 11.6. The two acidic groups are the two -OH groups, indicated by arrows in the structure. If we let AH₂ represent ascorbic acid, its successive ionized species can be abbreviated by ⁻AH and A²⁻.
Draw the structure of ⁻AH and its two resonance structures. Draw the curved arrow notation to convert each structure to the next. (Hint: In one structure, charge is delocalized into the C=O group.)