Ultraviolet Absorption Spectra of Three Isomeric Pyridine Monocarboxylic Acids and Their N-Oxides

Abstract

Abstract The ultraviolet absorption spectra of 2-, 3- and 4-pyridine monocarboxylic acid and their N-oxides were measured in various solvents. The absorption spectra of these compounds with the exception of picolinic acid show the blue shift with the change of the solvent from dioxane to ethanol and water. The absorption band of picolinic acid occurs in the region of the shorter wavelength than that of isonicotinic acid; this fact may be caused by the formation of the intramolecular hydrogen bond, which prevents the resonance of this molecule. The absorption band of picolinic acid N-oxide occurs in the region of the shorter wevelength than that of nicotinic or isonicotinic acid N-oxide, for which the present author attributed the formation of the intramolecular hydrogen bond and the steric interaction in picolinic acid N-oxide. We also observed the n–π* absorption in picolinic acid N-oxide.