An X-ray crystallographic, 1H nuclear magnetic resonance, and MNDO SCF-MO conformational study of o-substituted N-benzylbenzothiohydroxamic acids

Abstract

An X-ray determination of the structure of N-benzyl-o-methoxybenzothiohydroxamic acid (1a) shows the compound to have the Z-configuration with an intramolecular OH ⋯ S hydrogen bond [2.822(3)Å]. The nitrogen centre is planar, and the C-aryl group is orthogonal to the CNOH plane. ¹H and ¹³C n.m.r. studies suggest that in non-polar solvents o-substituted N-benzylbenzothiohydroxamic acids retain the Z-configuration, whereas in polar solvents such as dimethyl sulphoxide or methanol the E-isomer is also present. The activation parameters for rotation about the aryl to (thio)carbonyl C–C single bond have been measured by a variable-temperature lineshape analysis of the ¹H AB quartets due to the diastereoisotopic N-benzylic methylene protons. The results are compared with those of MNDO SCF-MO calculations.