Methods for the determination of molecular mobility of adsorbed molecules based on high resolution NMR

Based on the increased resolution achieved in NMR on adsorbed molecules, various methods are proposed to determine the mobility of adsorbed species. H-1 NMR linewidths are shown to reflect intramolecular dipolar relaxation and can therefore be used for mobility estimates. This method is applicable to extremely low loadings. Thus we measured a significant decrease in molecular mobility for 1-butene adsorbed in zeolite NaX at loadings of approximately one molecule per ten supercages compared to that observed at four molecules per supercage. H-1 NMR cross-relaxation rates of adsorbed allyl alcohol have been determined by 2D NOESY experiments and used to calculate the mean reorientation time of the allyl group. H-1-C-13 cross-relaxation rates, calculated using NOE factors and C-13 longitudinal relaxation rates, allowed the calculation of mean reorientation times of the CH bond vector for adsorbed 1-butene. The same results are obtained from a comparison of longitudinal relaxation rates of protons attached to C-13 and C-12 atoms. Finally, the relaxation behavior of molecular groups, including cross-correlation effects and hence generation and decay of multiple spin order, is examined for 1-butene adsorbed on NaX.