Infrared spectroscopic study of lactams of 6-amino-6-deoxyhexonic acid and of their tetra- O-acetyl derivatives in the CO and NH stretching vibration regions

Abstract

Infrared spectra were measured for eight diastereoisomeric lactams of 6-amino-6-deoxyhexonic acid and their tetra- O-acetyl derivatives in the regions of 1800-1600 and 3500-3000 cm −1 in the solid state (Nujol mulls) at room and liquid nitrogen temperature and in solutions at room temperature. Analysis of the IR spectra combined with the analysis of x-ray diffraction data for two of the isomers (the d-allo and d-manno configurations) suggests that the tetra- O-acetyl derivatives in the solid state form chain-like molecular structures. For lactams with the d-allo, d-galacto, l-gulo and d-talo configurations, the individual molecules are interconnected by intermolecular hydrogen bonds between the NH groups and the amidic CO groups, whereas for the d-altro, d-gluco, l-ido and d-manno isomers the amidic carbonyl groups are free, the intermolecular bonds occurring between the NH groups and the ester CO groups. The amidic carbonyl groups bonded by hydrogen bonds exhibit absorption at 1670-1660 cm −1, whereas the free groups absorb at 1710-1690 cm −1.