Intramolecular hydrogen bonding in ortho-substituted N,N-dimethylbenzamides

Abstract

Intramolecular hydrogen bonding in o-hydroxy-, o-amino- and o-mercapto- N,N-dimethylbenzamide has been examined with the help of ¹H, ¹³C n.m.r. and infrared spectroscopy, a study of barriers to rotation about the C- N bond, and a study of substituent effects using a multi-substituent parameter equation. The cyclic intramolecular hydrogen-bonded structure for the o-mercapto compound is non-planar, and conformational isomers have been detected. The order of relative energies of the hydrogen bonds formed in o-substituted N,N-dimethylbenzamides is OH > NH₂ > SH, as determined from a rotational barrier probe. It has beenverified that intramolecular hydrogen bonding causes a downfield shift of the ¹³C n.m.r. chemical shift of the carbonyl group in these compounds.