AM1 study of proton-transfer reactions of barbituric acid

✍ Scribed by Rita Kakkar; Vandana Katoch

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 205 KB
• Volume: 74
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/(sici)1097-461x(1999)74:3<327::aid-qua5>3.0.co;2-o

✦ Synopsis

The AM1 method is used to study the mechanisms of intra-and intermolecular proton transfer in barbituric acid. In the vapor phase, of the three possibilities, although thermodynamic factors favor the migration of a methylene proton to a neighboring oxygen, kinetic effects favor proton transfers from imine nitrogens. The intervention of a single water molecule has a dramatic effect on the activation barrier, bringing it down significantly, particularly for the methylene proton transfer. Several factors, including the reduction in the strain in the transition state, charge-transfer effects, ionic resonance, and solvent effects were analyzed to explain this. Bulk dielectric effects further reduce the activation energies for the proton transfers. Substituents at the 5-position, however, do not seem to have much effect on the activation barriers. ᮊ 1999