A carbon-13 cp/mas NMR investigation of the conformation of substituted cyclohexanes in thiourea inclusion compounds

Abstract

Inclusion compounds of several monosubstituted cyclohexanes and thiourea have been studied using high-resolution 13C CP/MAS NMR spectroscopy. The 13C NMR chemical shifts of the substituted cyclohexane ring are sensitive to the conformation of the substituent and allow one to predict qualitatively the relative populations of the axial and equatorial conformers. For methylcyclohexane trapped in thiourea the methyl substituent prefers the equatorial conformation while for the cyclohexyl halides (Cl, Br and I) the axial conformer is preferred. In the case of fluorocyclohexane the equatorial conformer appears to predominate; however, this conformer is in rapid equilibrium with the axial conformer.