Abstraet. Single crystals of Dianin's inclusion eompound with methyl and ¡ deuterated p-xylene guest molecules were grown and studied by FT deuteron NMR. The spectra from the deuterated methyl groups reveal that these groups reo¡ rapidly down to 12 K; thereat~er they enter hato the tunneling regime. The rings of the p-xylene guests become motionless when T reaches 110 K. By measu¡ the orientation dependence of the quadrupole splittings, determining from these data the quadrupole eoupling tensors of the ring deuterons and relating these tensors to the C-D bond directions we infer the sites of the p-xylene guests in the cages of Dianin's inclusion compound. We final two sets of independent sites. Each contains three C 3 related individual sites. In each set the population of one of the sites is strongly depleted. The only large-angle molecular motions are 180 ~ rotational jumps about the long molecular axes. From measurements of T~ we conclude that these jumps are thermally activated, ro = 5.10 -~4 s, AE = 20 kJ/mol. Additional motions are rapid librations, also about the iong molecular axes. Their amplitude increases with increasing temperature, at 300 K it reaches 20 o. With 2D-exchange speetra we demonstrate that a p-xylene guest cannot change its site on a timescale of 100 ras anda tempe¡ expe¡ suggests that this is true on a timescale of several days even at T = 371 K.
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