Solid‐state 13C NMR investigations of monosubstituted cyclohexanes in thiourea inclusion compounds

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Abstract
Thiourea inclusion compounds with substituted cyclohexanes bearing polar or non‐polar substituents were studied by dynamic 13C magic angle spinning NMR spectroscopy. Variable‐temperature experiments were performed to evaluate the specific features of the guest molecules comprising both the kinetic and the thermodynamic aspects. Further information was also obtained about potential guest‐host interactions which might have a bearing on the molecular behaviour of the guest species. Quantitative analysis in these experiments revealed that within the temperature range covered, the relaxation behaviour is dominated by ring interconversions of the guest molecules. In addition, reorientational motions of the guest molecules exist on a very fast time‐scale which are responsible for the observed significant reduction in the anisotropic magnetic interactions. The most prominent results are the evaluated unusual conformational equilibria. It is shown that the thiourea host lattice obviously stabilizes the axial conformational state. This is true for all systems with polar substituents whereas for those with non‐polar substituents the conformational equilibria are not affected. These findings are related to specific guest‐host interactions, probably of a polar nature.

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