Solvent effects on the energetic parameters and chemical reactivity in the keto–enol tautomeric equilibrium of substituted carbonyl compounds

A density functional theory model analyzes the effect of the presence of the solvent on the activation barrier and the reaction energy in the keto–enol tautomeric equilibrium for acetaldehyde and related compounds. Continuous and explicit (microsolvation) models are used to simulate the effect of the solvent. The continuous solvent model marginally changes the activations barrier, while the formation of complexes with water molecules lowers the barrier up to 47 kcal/mol, with respect to the gas phase values. The analysis of the change in some local reactivity parameters of the solute molecules, coming from the solvent presence, shows that the hydrogen bonds in the solute–solvent complexes strongly modify the molecular electrostatic potential of the involved molecules, while the donor Fukui function practically remains unchanged. The molecular electrostatic potential is also more sensitive to the inductive substituent effects than the Fukui function.