Three series of substituted pyridines have been prepared having substituents in various positions on the ring. Although there were variations in the chemical nature and in the position of these substituents, it was found that certain fundamental absorption bands are typical of all the pyridines studied. The separation of the two bands in the 1600-1500 cm<sup>−1</sup> region does not appear to be helpful in determining the position of substituents, but absorption in the 950-750 cm<sup>−1</sup> region does give a clue as to the number of adjacent hydrogens on the pyridine ring There appears to be a band very characteristic of the cyclohexeno ring, thus confirming previous work. In addition, a band was found which is due to the cyclohexeno ring, as modified by the attached pyridine ring. There seems to be absorption characteristic of the cyclohepteno ring. Correlation is made of the several substituent groups when attached to the pyridine ring, as compared to the same groups attached to the benzene ring.
Edith M. Godar and Raymond P. Mariella, "Infrared Spectral-Structural Correlations of Some Substituted Pyridines," Appl. Spectrosc. 15, 29-33 (1961)