ON THE HYDROGEN-BONDED STATUS OF 2-AZACYCLONONANONE AND 2-AZACYCLOTRIDECANONE IN THE SOLID-STATE

Triggs et al. (J. Phys. Chem. 1993, 97, 5535) have recently reported the results of a preresonant Raman study of 2-azacyclononanone (2) and 2-azacyclotridecanone (3) in the solid state. These workers examined a number of spectroscopic features and concluded that ''all the Raman spectral indicators of hydrogen bonding are negative'' for these two lactams. We have compared the published Raman data for 2 and 3 with IR data from older literature and new FT-IR data; the comparison reveals that determination of these molecules' hydrogen-bonded state in the solid is not as straightforward as implied by Triggs et al. Previously, hydrogen bonding of amide groups has most commonly been deduced from the position of the N-H stretch band. According to the conventional interpretation, the N-H stretch band positions for 2 and 3 indicate that these molecules are hydrogen bonded in their crystalline forms. We suggest that the variations in Raman spectroscopic features reported by Triggs et al. stem from effects that are more subtle than simply the presence or absence of hydrogen bonding.