Chart 1. Neutral, Singly Protonated, Doubly Protonated, and Deprotonated Forms of 1a.
a Only one tautomeric form is shown for the neutral and cationic species. For the anion, only one resonance form is shown.
a Only one tautomeric form is shown for the neutral and cationic species. For the anion, only one resonance form is shown.