The Effect of Intramolecular Hydrogen Bonding on the Rotational Barriers about the C–N Bonds of o-Hydroxyarenecarboxamides

Rotational barriers about the C–N bonds of several o-hydroxyarenecarboxamides were determined in four solvents (namely, chloroform, pyridine, methanol, and dimethyl sulfoxide) by DNMR spectroscopy and compared with those of arenecarboxamides void of ortho-hydroxyl group. The height of the rotational barrier is correlated with the strength of the intramolecular O–H···O=C hydrogen bond. The unusual solvent effect on the rotational barriers of these hydroxy–amides are ascribed to the cleavage of the intramolecularly hydrogen bonded chelate ring which occurs in both hydrogen-donating and -accepting solvents.