Hydrogen bonding in barbituric and 2-thiobarbituric acids: a theoretical and FT-IR study

The effects of intermolecular hydrogen bonding on the molecular properties of barbituric acid (BA) and thiobarbituric acid are discussed on the basis of density functional theory calculations. B3LYP methods were applied to mo nomers and cyclic dimers. Trimer and hexamer of BA were studied as examples where several C=O and NH groups are involved in hydrogen bonding. The theo retical IR spectra of monomers and all oligomers here considered are compar ed with the FT-IR spectra measured in Ar and nitrogen matrices at different concentrations. (C) 2001 Elsevier Science B.V. All rights reserved.