Solvent and structural effects in tautomeric 3-cyano-4-(substituted phenyl)-6-phenyl-2(1H)-pyridones: experimental and quantum chemical study

The tautomeric equilibria between 2-pyridone and 2-hydroxypyridine forms of methoxy, chloro, and nitro derivatives of 3-cyano-4-(2-, 3-, and 4-substituted phenyl)-6-phenyl-2(1H)-pyridones were evaluated from UV/Vis spectral data. Linear solvation energy relationships of Kamlet-Taft and Catalan-rationalized solvent have influence on tautomeric equilibria. Transmission of substituent effect was analyzed by the Hammett equation. Quantum chemical calculations were performed by density functional theory (B3LYP). The experimental data were interpreted with the aid of time-dependent density functional method. Electron density distribution was analyzed by Bader's analysis. It was found that substituents of different electronic properties change the extent of conjugation, and affect intramolecular charge transfer character. Theoretical calculations and experimental results gave insight into the influence of the molecular conformation on the transmission of substituent effects, as well as on contribution of different solvent-solute interactions.