Theoretical study of the effect of water clusters on the enol content of acetone as a model for understanding the effect of water on enolization reaction

The enolization of simple carbonyl compounds is a key reaction for many chemical and biochemical processes. Numerous theoretical and experimental studies have been done to probe aspects of the mechanism of this reaction. In this work, the effect of small water clusters, (H 2 O) n , n = 1–9, on the enol content of acetone has been investigated by using density functional theory calculations at the M06 level of theory in the gas and solution phases. The calculations indicated that the formation of hydrogen-bonded assemblies between water clusters and both tautomers of acetone affect the enolization reaction. Among them, the trimeric water cluster has the highest binding energy difference (Δ E b ) in the solution phase and greatly shifts the equilibrium in the favor of the enol form. The results also show that under this condition, the enol content of acetone increased with decreasing polarity of the solvent. The practical conclusion of this study is that the enol content of carbonyl compounds can be maximized only by addition of a defined amount of water.