Theoretical and Infrared Spectroscopic Considerations on the Keto-Enol Tautomerization and Proton-transfer of the 2-Pyridone--Acetic Acid System in the Ground State

Kozo INUZUKA

Department of Material Science and Engineering, Faculty of Engineering, Tokyo Denki University; Kanda, Chiyoda-ku, Tokyo 101-0054 Japan

In order to make clear the possibility of the keto-enol tautomerization and its mechanism in the 2-pyridone--acetic acid system in the ground state, the density-functional theoretical calculations at the B3LYP/6-31G(d) and B3LYP/6-31G(d, p) levels with a geometry-optimization were carried out for the 2-pyridone--formic acid system used as a model system. And the IR spectrum of 2-pyridone--acetic acid system was measured to ascertain the 2-pyridone--acetic acid complex (abbrev.: keto complex), the 2-hydroxypyridine(2-pyridinol)--acetic acid complex (abbrev.: enol complex) and 2-hydroxypyridinium acetate (abbrev.: cation complex) which were speculated to form in the keto-enol tautomerization process of the 2-pyridone--acetic acid system in the ground state. The calculated results suggest that the keto-enol tautomerization may occur in the 2-pyridone--formic acid system used as a model system from the magnitudes of the stabilization energies of the keto and enol forms and the potential energy height of the tautomerization process through the cation form.
Experimentally, the characteristic bands ascribed to the keto, enol and cation complexes were observed in the IR spectrum of the 2-pyridone--acetic acid system. These results suggest that the keto-enol tautomerization may occur in the 2-pyridone--acetic acid system through the cation complex in the ground state.



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