17O NMR studies of torsion angle relationships in aryl alkyl ketones and aromatic aldehydes

Abstract

Abstract17O NMR spectroscopic data, at natural abundance, in acetonitrile at 75 °C were obtained for a series of phenyl alkyl and cycloalkyl ketones, benzophenone, methyl alkyl ketones, three fused‐ring aryl ketones and a series of variously hindered aromatic aldehydes. The trend in chemical shifts for the relatively unhindered alkyl aryl ketones is a general increase in shielding with increasing size of the alkyl group. However, when steric hindrance becomes significant, torsion angle rotation occurs and deshielding is observed. Cyclopropyl ketones show much larger shielding effects than their isopropyl analogs. Torsion angles for aryl ketones and aromatic aldehydes are estimated using an indirect method based on previous results from electronically similar hindered ketones.