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.
We demonstrate by selective saturation deuteron NMR experiments on a deuterated crystal of bis-(4-chlorophenyl)-sulphone (BCPS, the `butterfly molecule’) that, in the crystalline state, the two phenyl rings of this molecule are flipping through 180° . This process is thermally activated, the kinetic parameters are ΔE = (71+-5) kJmol- 1 and k0 = 1015.56+-0.8 s- 1. Our spectra also indicate a slow magnetization transfer, on a time scale of 50 s at room temperature, between deuterons located on different wings of the molecule. Flips of the molecule as a whole about a crystal and molecular twofold axis would account for this magnetization transfer. An alternative explanation is spin diffusion. To discriminate between these two possibilities we develop and apply a new criterion. It exploits the fact that the sign of quadrupolar order transferred between two I = 1 spin ensembles with quadrupole splittings of opposite sign depends on whether the quadrupolar order transfer occurs via chemical exchange or via spin diffusion. This criterion thus allows one, in a single experiment, to discriminate between chemical exchange and spin diffusion in a yes/no fashion. We therefore call it binary quadrupolar order criterion. Its application to BCPS yields the result that the observed slow magnetization transfer is due to spin diffusion and that the BCPS molecules are not flipping as a whole on a time scale of 50 s at room temperature
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