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

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.