Tautomeric Transformations and Reactivity of Polyfunctional Hydroxypyrimidines: IV. Effects of Tautomer Structure and Acidity and Solvent Nature on the State of Tautomeric Equilibria in the Series of 5-Nitro Derivatives of 2,4,6-Pyrimidinetrione
Authors: Slesarev, V. I.; Popov, A. S.
Source: Russian Journal of General Chemistry, Volume 74, Number 3, March 2004 , pp. 414-422(9)
Publisher: MAIK Nauka/Interperiodica
Abstract:Tautomeric equilibria of 5-nitrobarbituric acid and 1,3-dimethyl-5-nitrobarbituric acid were studied by NMR, UV, and IR spectroscopy, as well as by quantum-chemical methods. These compounds were found to exist in the gas phase, in solutions in water and DMSO, and in crystal as the corresponding enol tautomers. In trifluoroacetic and chloroform solutions, an equilibrium mixture of the ketone and enol forms was detected. The parameters determining the state of the tautomeric equilibrium are the total energy of a tautomer, its deprotonation energy, and a component of the latter, which relates to electrostatic interaction between the mobile proton and the rest of the molecule. Proton-donor and proton-acceptor properties of the solvent and 5-nitro-2,4,6-pyrimidinetrione derivatives are the main factors responsible for displacement of the tautomeric equilibrium in solution; electrostatic solvation and tautomer stabilization via hydrogen bonding are less significant.
Document Type: Research Article
Affiliations: Mechnikov St. Petersburg State Medical Academy, St. Petersburg, Russia
Publication date: March 1, 2004