The ultraviolet spectra of the chloropyridines and chlorinated pyridines possessing a sulfur (-SR), nitrogen (-NR2), or oxygen (-OR) substituent in either the 2 or 4-position: A convenient method for distinguishing such positional isomers

The ultraviolet spectra for a series of 15 chlorinated pyridines which contain a sulfur, nitrogen or an oxygen substituent at either the 2 or 4-position have been examined. A correlation has been established between the position (2 vs 4) of the S, N, or O substituent on the chlorinated pyridines and their ultraviolet spectra. It was found that the chlorinated pyridines with S, N, or O substitution at the 2-position gave ultraviolet spectra whose longest wavelength absorption maxima were enhanced (moved to a greater wavelength and an increased extinction coefficient) when compared to the spectra of the 4-substituted isomers. The difference is great enough so that an easy identification of positional isomers can be made with a relatively high degree of confidence even when only one positional isomer is available. The ultraviolet spectra of all the chlorinated pyridines has been recorded, and it was observed that the number of chlorine atoms, and not their position, was the more significant factor in determining the overall character of the spectra.