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AM1 study of proton‐transfer reactions of barbituric acid
Author(s) -
Kakkar Rita,
Katoch Vandana
Publication year - 1999
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(1999)74:3<327::aid-qua5>3.0.co;2-o
Subject(s) - chemistry , proton , intermolecular force , barbituric acid , methylene , ionic bonding , solvent , molecule , imine , phase (matter) , computational chemistry , photochemistry , organic chemistry , catalysis , ion , physics , quantum mechanics
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. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 74: 327–336, 1999