The identification of the position of the C=S absorptions in the IR-spectra of thioureas, thioamides, thiolactams and similar compounds has been a difficult matter1. Just as with the carbonyl group, the C=S absorption was found to be sensitive to the nature of the surrounding structure. Mecke et al2,3compared the carbonyl and thioketone spectra of different compounds of various types. Their priliminary calculations indicated that the ratio νC=O/νC=Swould be about 1.5 and that the C=S frequency would be found in the 1200-1050 cm−1region. Thompson4suggested a range of 1400-1300 cm−1for this absorption. And Randall and his co-workers5have drawn attention to a strong band occuring between 1613 cm−1and 1417 cm−1in the thioureides they studied. Also the C(O)-NH absorption has been the subject of much controversy. The origin of a strong band at rather lower frequencies in secondary amides has been variously assigned as an N-H deformation mode, a C(O)-N stretching mode and as a mixed vibration involving both types of motions. The difficulty in assigning the C=S stretching frequency was in part due to relativey fewer compounds available for the study. Also, the structural dissimilarity of the compounds atudied led to variable assignments of the compounds studied led to variable assignments of the C=5 stretching frequency by different investigators.