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

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 5Jcis/5Jtrans 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 5Jcis/5Jtrans is greater than 1.