Ab initio and density functional calculations on the ring-chain tautomerism of gamma-oxocarboxylic acids

The results of ab initio (HF, MP2) and density functional (B3LYP) calculati ons on a series of gamma -oxocarboxylic acids [(Z)-3-acetyl or benzoylacryl ic and 2-acetyl or benzoylbenzoic acids] A and their cyclic tautomers B are presented. For the open-chain tautomers, different rotamers were considere d. Bulk solvent effects were considered by using the polarised continuum mo del (PCM) and were found to be essential for a proper description of the ri ng-chain tautomeric equilibrium. Acetyl derivatives generally prefer the cy clic form, whereas for benzoyl derivatives the preference depends on the na ture of the Link. Introduction of substituents (methyl, phenyl) at C2 and/o r C3 for acrylic acid derivatives substantially shifts the equilibrium towa rds the cyclic form B.