Infrared spectra in the range (4000-250 cm-1) and Raman spectra in the range (4000-150 cm-1) of pyridine, 2-, 3- and 4-chloro-, bromo-, and methylpyridines, 2-fluoro-, 2-amino and 4-ethylpyridines have been measured. The spectra, vibration and assignments of the observed frequencies of 2-amino-, and 4-ethylpyridines are presented for the first time. The infrared data for 2-fluoropyridine is combined with the previously reported Raman data of Stephenson and Voelz to allow complete vibrational assignments for this compound for the first time. Frequency assignments for the other molecules are re-examined and where necessary changes and/or additions in frequency assignments are made.
Correlations between related series of pyridine and pyridine derivatives are investigated. The possible correlations between the vibrations of monosubstituted pyridines and the corresponding vibrations of monosubstituted benzene compounds were studied and it was found that they show a few similarities. Also, the location of the substituted on the ring is seen to influence the frequency of some of the vibrations. Further, other than C-H stretching vibrations, 5 vibrational modes are similar for the 1-, 2-, and 3-substituted pyridines (i.e., frequencies are independent of the location of the substituent and analogous to the corresponding vibrations of the monosubstituted benzene compounds. The correlations between a substituted pyridine and a monosubstituted benzene are seen to be useful in making vibrational assignments on other related compounds
