Influence of carboxylic acid association upon the lactim–lactam tautomeric equilibrium of 2-hydroxypyridines

Abstract

I.r. and u.v. absorption spectroscopy in CCl₄ at room temperature provides evidence for lactim–acid and lactam–acid heterodimer formation in 6-chloro-2-hydroxypyridine–acetic acid mixtures. Measurements of association constants for two types of 1:1 hydrogen-bonded complexes reveal preferential association with the lactam tautomer, leading to a shift in the apparent tautomeric equilibrium constant. These results suggest that specific interactions are of great importance in understanding solvent effects on protomeric equilibria.