1H, 13C, 15N, 2D and variable temperature NMR study of the role of hydrogen bonding in the structure and conformation of oxamide derivatives
The structure and conformation of N,N′-bis[(2-hydroxy)phenyl]oxamide (1); N,N′-bis[(2-methoxy)-phenyl]oxamide (2); N,N′-bis(phenyl)oxamide (3); N,N′-bis[(1R,2S)-(–)-norephedrine]oxamide (4); N,N′-bis[(1R,2R)-(–)-norpseudoephedrine]oxamide (5); N-[(2-hydroxy)phenyl]methylamide (6); N-[(2-methoxy)phenyl]methylamide (7); N-phenylmethylamide (8); N-[(–)-norephedrine]-methylamide (9) and N-[(–)-norpseudoephedrine]methylamide (10) were unambiguously established by 1H, 13C, 15N, 2D and variable temperature NMR spectroscopy. A careful NMR investigation of the conformational behaviour in these systems was relevant. It has been found that the dicarbonylic group in compounds 1–5 has a trans geometry, stabilized by intramolecular hydrogen bonding and that they possess a C2 axis. Compounds 1 and 2 are planar and compounds 1, 2, 4 and 5 present the amidic proton coordinated by two oxygen atoms.