Wide-line deuterium NMR

More detailed information on motion within the Cig chains, at least the timescales that are relevant, are obtained by C NMR relaxation studies [5p]. Several C NMR studies of Cig-derivatized silicas and other n-alkyl analogs have been reported [5n,p,37] Even more detail on the motion can be obtained by wide line H NMR spectroscopy (a technique that does not have high resolution) on Cig-silica samples in which deuterium has been selectively substituted for protons [50]. In this approach, the line-narrowing effects of motion on the broad, quadrupole-based H NMR linewidth of a mechanically static sample is modeled theoretically for specific trial motions to elucidate the detailed nature of the motion. As an example. Figure 34.32 shows experimental H spectra, and the corresponding theoretical simulation for a dry sample of (l-d2)-Ci8-silica as a function of temperature. From the theoretical simulations, based on trial... 

Using dynamic solid-state CP MAS NMR spectroscopy, the kinetics of the degenerate intermolecular double and quadruple proton and deuteron transfers in the cyclic dimer of N labelled polycrystalline 3,5-diphenyl-4-bromopyrazole (DPBrP) and in the cyclic tetramer of N labelled polycrystalline 3,5-diphenylpyrazole (DPP) have been studied in a wide temperature range at different deuterium fractions in the mobile proton sites. Rate constants were measured on a millisecond time scale by line shape analysis of the doubly N labelled eompounds and by magnetisation transfer experiments on a second timescale of the singly N labelled compounds in order to minimise the effeets of proton-driven N spin diffusion. The Arhenius curves of all processes were found to be nonlinear and indicated tunneling processes at low temperatures. In a preliminary analysis, they were modelled in terms of the Bell-Limbach tuimeling model. 

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