Stereochemical analysis of aromatic oximes. 13C–15N nuclear spin coupling and 13C shieldings as conformational probes

Abstract

13C nmr chemical shifts and 13C–15N spin couplings over one, two, and three bonds are reported for six aromatic oximes including two benz annelated compounds. Preferred geometries have been calculated via the GEMO program. Fermi contact contributions to carbon–nitrogen coupling have been evaluated and, in general, agreement between experimental and theoretical values is poor. Vicinal 13C–15N couplings are shown to depend on both dihedral angle and oxime valence angle. Oxime carbon chemical shifts do not provide a measure of deviation from planarity between the oxime group and the aromatic ring.The sign of 1JCN in E-benzaldoxime has been determined to be negative.