CONFORMATIONAL PROPERTIES OF MONOSUBSTITUTED CYCLOHEXANE GUEST MOLECULES CONSTRAINED WITHIN ZEOLITIC HOST MATERIALS - A SOLID-STATE NMR INVESTIGATION

The conformational properties of monosubstituted cyclohexane guest mol ecules (C6H11X with X = CH3, OH, Cl, Br and I) included within micropo rous solid host materials (silicalite-1, H-ZSM-5, NH4-mordenite and ze olite NH4-Y) have been elucidated via high-resolution solid-state C-13 NMR spectroscopy. For all of the inclusion compounds investigated, th e fraction of monosubstituted cyclohexane molecules in the equatorial conformation is similar to that in solution, suggesting that these hos t materials do not impose any significant constraints upon the conform ational properties of the monosubstituted cyclohexane guest molecules. For the monohalogenocyclohexane guest molecules (C6H11X with X = Cl, Br and I), this result is in marked contrast to the situation for the same guest molecules in the thiourea host structure, for which the con formational properties of the guest molecules are substantially differ ent from those of the same molecules in solution. For cyclohexanol (C6 H11OH) in H-ZSM-5, some amount of dicyclohexyl ether (C6H11OC6H11) is observed, and is analogous to the proposed production of dimethyl ethe r in the first stage of methanol-to-gasoline conversion on this zeolit e. The comparatively low temperature (ambient temperature) at which th is conversion from cyclohexanol to dicyclohexyl ether occurs is notewo rthy. In addition to our high-resolution solid-state C-13 NMR studies of these materials, H-1 MAS and Al-27 MAS NMR spectra have also been r ecorded, and are discussed.