Abstract
The infrared spectra of over ten kinds of α-, β-, and γ-substituted pyridines (38 compounds) were determined. The displacement of ring CH out-of-plane bending frequencies following the change in nature of the substituent as well as in its position was discussed. A series of weak absorptions in the region of 990 and 1220 cm-1 was found to be very characteristic for the type of substitution. The relative intensity of the two bands between 1550 and 1620 cm-1, which originate in ring double-bond stretching vibrations, was found to be directly related to the type of π-electron distribution on the ring. The electronic effect of ring nitrogen toward each position of the ring was found to appear regularly as a frequency shift in the absorption of ring substituent. The linear correlations between the frequencies and σ-values of the substituents in substituted benzene derivatives could be extended to the substituted pyridines, by using the σ-values of 0.93, 0.62, and 1.02 respectively for 4-, 3-, and 2-position of the pyridine.
