“…Although the keto forms are generally favored in aqueous solution, the keto-enol tautomer equilibria may be dependent on forward “enolization” ( k E 0 , k E 1 , k E 2 ) and reverse ( k K 0 , k K 1 , k K 2 ) “ketonization” or deprotonation at the β-carbonyl oxygen (p K a3 , p K a4 ) to form enolates (shown in Scheme ). Although UV–visible spectroscopy has been used to confirm the π → π* transition of the αβ carbonyl π-system associated with “H 3 Acdica (enol) ” (242 nm, ε = 294 M –1 cm –1 ) and enolate anion “Acdica 3– ” (268 nm, ε = 346 M –1 cm –1 ), a significant increase in the decarboxylation rate constant of H 2 Acdica 1– (2.90 × 10 –3 min –1 ) in comparison to that of H 3 Acdica (1.25 × 10 –3 min –1 ) and HAcdica 2– (0.10 × 10 –3 min –1 ) led the authors to suggest a six-membered enol transition state to explain the increase. , There is no mention in the current scientific literature on the possible ( k E 0 , k E 1 , k E 2 ) and ( k K 0 , k K 1 , k K 2 ) values and p K a ’s (p K a3 , p K a4 ) for acetonedicarboxylate (shown in Scheme ), but we mention them here because the enol and enolate forms of the ligand play a strong role in coordination to metal ions …”