The vibrational spectra of 4-pyridone, and its 2,3,5,6-tetradeutero, N-deutero, N-methyl, N-cyano, and 3,5-dihalogeno derivatives. Mixing between C=C and C=O stretching vibrations

Abstract

The infrared spectra of the above compounds, and the Raman spectra of the parent compound and its 2,3,5,6-D₄, 1-D, and 1-Me derivatives have been determined. The effects of electron-withdrawing substituents, N- methylation, and deuteration on the two intense infrared bands in the 1480-1650 cm^-1 region are not compatible with one being a C=O and the other a C=C stretching band. These two vibrations must be extensively mixed; occasionally very pronounced medium effects, which are not straightforward, are observed for one or both of these bands. The spectra are not in accord with a mostly zwitterionic (N-protonated pyrid-4-oxide) structure (II) of 4-pyridone. Band assignments are made for the parent compound.