Chemical shifts of bromomethine protons of constrained α-bromocyclohexanones An index of configuration and conformation

Abstract

The chemical shifts due to the bromomethine proton have been listed for 36 α-mono- and α,α-dibromocyclohexanones which are conformationally constrained. The values observed are a remarkably reliable index of the axial or equatorial nature of the protons in question. The presence of Me or methylene substituents, a second Br atom, a heterocyclic O atom or a carbon bridge seems to have little direct effect on the shift position which is principally influenced by the geometry of the methylenemethine ketone grouping in the time-averaged species. Consequently the shift position can be used to assign configuration and to assess conformational preferences.