A study of the tautomerism of β-dicarbonyl compounds with special emphasis on curcuminoids

Six beta-diketones related to curcumin and curcumin itself have been studied by C-13 NMR spectroscopy in chloroform in order to determine the equilibrium constant between the two keto/enol tautomers. In order to do this GIAO/B3LYP/6-31G** calculations of absolute shieldings (sigma, ppm) were carried out. To establish relationships between sigma and experimental chemical shifts (delta, ppm), three simple beta-diketones (acetylacetone, dibenzoylmethane and benzoylacetone) have been studied. The preference for different groups to be conjugated with the C=O has been determined. (C) 2008 Elsevier Ltd. All rights reserved.