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The ultraviolet absorption spectra of the carboxyl group of three isomeric  pyridine carboxylic acids N-oxides (picolinic acid N-oxide, nicotinic acid  N-oxide and isonicotinic acid N-oxide) were determined in fourteen solvents  in the wavelength range from 200 to 400 nm. The position of the absorption  maxima (λmax) of the examined acids showed that the ultraviolet absorption  maximum wavelengths of picolinic acid N-oxide are the shortest, and those of  isonicotinic acid N-oxide acid are the longest. In order to analyze the  solvent effect on the obtained absorption spectra, the ultraviolet absorption  frequencies of the electronic transitions in the carboxylic group of the  examined acids were correlated using a total solvatochromic equation of the  form max = v0 + sπ + aα+ bβ, where υmax is the absorption frequency (1/λmax),  p is a measure of the solvent polarity, β represents the scale of solvent  hydrogen bond acceptor basicities and α represent the scale of solvent  hydrogen bond donor acidities. The correlation of the spectroscopic data was  carried out by means of multiple linear regression analysis. The solvent  effects on the ultraviolet absorption maximums of the examined acids were  discussed

The effects of solvents and structure on the electronic absorption spectra of the isomeric pyridine carboxylic acid N-oxides