Quantitative Analyses of Stereoisomeric 3,4-d2-Cyclohexenes in the Presence of 3,6-d2-Cyclohexenes

The challenging analytical problem posed by mixtures of the four isomeric 3,4-d(2)-cyclohexenes and the three isomeric 3,6-d(2)-cyclohexenes has been solved through a novel one-dimensional NMR spectroscopic method dependent on recording C-13 resonances while broadband decoupling both proton and deuteron nuclei. Upfield deuterium perturbations of C-13 chemical shifts in chair conformationally locked cyclohexane derivatives readily secured from a mixture of the seven deuterium-labeled cyclohexenes allow quantitative analytical assessments of the four possible 3,4-d(2)-cyclohexenes in the mixture. This analytical capability is an essential prerequisite for uncovering the relative participations of the four possible stereochemical paths followed by the thermal structural isomerizations of vinylcyclobutane to cyclohexene. The unconventional NMR method validated in this work will likely prove invaluable in related stereochemical investigations.