Infrared spectra of tetrahydrophyrido[1,2-a]pyrimidin-4-one derivatives

Abstract

During the infrared spectrometric investigation of a considerable number of 1,3-dicarbonyltetrahydropyridopyrimidine derivatives, frequency coupling of v(CO), O-cis, O-trans conformations and polymorphism were observed. It is generally accepted that the magnitude of the frequency coupling is characterized by the band shifts and by the intensity difference of the coupled vibrational bands. However, for the tetrahydropyridopyrimidine derivatives studied here only the intensity difference of the coupled bands is characteristic of the extent of the coupling of vibrations. The frequency difference of the coupled bands depends primarily on the chemical environment.