Orbital interactions in 2-Halocyclohexanones as analyzed by means of theoretical calculations

Abstract

The stereoelectronic interactions governing the conformational isomerism of 2-halocyclohexanones have been investigated by using an isodesmic reaction model. It has been found that 2-axial halogenation of cyclohexanone is thermodynamically favoured, whilst insertion of an equatorial bromine or iodine is not. Overall, inclusion of axial halogens in cyclohexanone is preferred to equatorial entrance and, according to NBO calculations, this behaviour is due to electron donation from nonbonding and C-X orbitals to πCO∗ antibonding orbital, in addition to steric and electrostatic effects.