Spectral characteristics of the bands of NH groups and structure of 2-thioxobenzazolines in solvents with low polarities

The IR spectra of five 2-thioxo-benzazolines in carbon tetrachloride (2500–3500 cm^–1) and chloroform (3200–3500 cm^–1) are examined. Analysis of the spectral parameters of the absorption band of the unassociated NH groups showed that the high proton-donor capacity of the hydrogen atom of the thioamide group of 2-thioxobenzoxazoline is evidently associated with the high electronegativity of the oxygen atom. The existence of intermolecular hydrogen bonds with a degree of dissociation of 0.3 in carbon tetrachloride and 0.1 in chloroform was established by means of the concentration dependence of the spectra. A change with time in the integral coefficient of the absorption band of the unassociated NH groups was observed in solutions in carbon tetrachloride; this is explained by interaction of the 2-thioxobenzazolines with carbon tetrachloride. The IR spectra, a table of the spectral characteristics, the dependence of the relative integral intensity on the concentration, and the dependence of the optical density of the absorption band of free NH groups on time are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 69–71, January, 1979.