Tautomeric Transformations and Reactivity of Polyfunctional Hydroxypyrimidines: III.~1 Tautomerism of 5-Acyl Derivatives of H-bonded Complexes with Solvents

摘要

Tautomerism of 5-formyl- and 5-acetyl derivatives of pyrimidine-2,4,6-trione, 2-thioxopyri-mine-4,6-dione, and 4,6-dihidroxy-2-methylthiopyrimidine was studied by NMR, UV, and IR spectroxcopy, as well as by quantum chemistry. An equilibrium mixture of exo- and endo-enols in the neutral state and the presence of the same tautomers in monoanions were found. The energies of intramolecular hydrogen bonds in the gas phase and their changes in going to solution in water, DMSO, and chloroform were calculated. The energies of intra- and intermolecular hydrogen bonds are close to each other. This fact suggests existence in solutions of two forms: tautomers with intramolecular H bond and H-bond. Characteristics of intermolecular fhydrogen bonds are determined by the relative proton-donor and proton-acceptor powers of polyhydroxypyridmidines and solvents and are almost independent of the polarity of the medium.