Conformational analysis of cyclohexa-1,4-dienes by nuclear magnetic resonance

Abstract

SCF–INDO–FPT calculations were performed for various geometries of the flat cyclohexa-1,4-diene molecule to obtain theoretical homoallylic coupling constants (⁵J). The values of ⁵J_cis/⁵J_trans remain within the narrow range 1.22–1.29. Thus, theoretical and empirical homoallylic coupling constants for a flat cyclohexa-1,4-diene molecule agree closely, and there is no need to postulate a rapidly inverting cyclohexa-1,4-diene ring. Other anomalies in the literature can be resolved once it is recognized that for a flat cyclohexa-1,4-diene molecule ⁵J_cis/⁵J_trans is greater than 1.