Abstract
The infrared spectra of eight ethylpyridines and nineteen methylpyridines were determined. The absorption spectra obtained are correlated with their structures and are discussed on the characteristic properties of the pyridine ring and its similarity to the benzene ring. The conclusion are as follows : (i) Out-of-plane C-H deformation frequencies in alkylpyridines are determined principally by the number of adjacent free hydrogen atoms round the ring in a similar way to substituted benzenes, (ii) furthermore, their exact frequencies have a distinct correlation with the arrangement of hydrogen atoms round the ring, (iii) ethylpyridines always absorb at higher frequencies than those of the corresponding methyl homologs, and (iv) pyridine ring vibrations between 1450 and 1650 cm-1 are also regularly correlated to the structures.
