The C=S stretching frequency and the "-N-C=S bands" in the infrared

Abstract

A correlation of the infrared spectra of thiocarbonyl derivatives based on the literature data has been carried out. Assignments have also been made in some new systems. Since simple alkyl thioketones are unstable, we have prepared thiofenchone in order to obtain a reference C=S stretching frequency. The C=S stretching frequency in thiofenchone has been found around 1180 cm⁻¹ which is in fair agreement with the value calculated for thioformaldehyde. In the case of the thiocarbonyl derivatives where the C=S group is linked to elements other than nitrogen, the stretching frequency is generally found in the region 1025-1225 cm⁻¹. Strong vibrational coupling is operative in the case of the nitrogen containing thiocarbonyl derivatives and three bands seem to consistently appear in the regions 1395-1570 cm⁻¹, 1260-1420 cm⁻¹, 940-1140 cm⁻¹ due to the mixed vibrations. These bands, which may be tentatively designated as the "-N-C=S I, II and III bands", could be useful in qualitative analysis.