Conformation and stereodynamics of N,N-dialkylbenzamides; a 1H and 13C nuclear magnetic resonance investigation of para-substituted 4-benzoyl-cis-2,6-dimethylmorpholines

Abstract

A high-field ¹³C n.m.r. study of the title compounds below –80 °C has enabled measurement of the barriers to rotation around the aryl–C(O) bond. These barriers (ΔG^‡ 7.7–9.5 kcal mol^–1), and those for rotation around the C(O)–N bond (ΔG^‡ 13.6–15.6 kcal mol^–1) determined by ¹H n.m.r. at higher temperatures, correlate well with Hammett σ⁺ substituent parameters. The ground-state conformation has the phenyl ring twisted out of the amide plane. Some ¹H and ¹³C chemical shift correlations are also reported.