Derivatives, proton spin-lattice relaxation

The proton-spin-lattice relaxation time, T , in a diamagnetic sample is typically dominated by the dipole-dipole interactions among the protons, and is particularly sensitive to molecular motions therefore, T values have been used widely to derive information about domain uniformity or phase separation in solids. In single-phase solids with an abundance of protons, the protons are usually so strongly coupled by homonuclear dipolar interactions that possible differences in proton spin-lattice relaxation are averaged out by spin diffusion, and a single T will be observed in this case. In heterogeneous samples, different T values can be observed for different phases. 

Figure 26.16 The temperature dependence ofthe jump rates ry for deuterium in TaViDos and TaVjDu, as determined from the spin lattice relaxation data [72], The solid lines show the fits of Eq. (26.29) to the data. The dashed line represents the behavior of Ty (l) for H in TaVjHo jj, as derived from the fit of Eq. (26.29) to the proton spin-lattice relaxation data (Ref [54]).

K. Bock, L. D. Hall, and C. Pedersen, Survey of the proton spin-lattice relaxation rates of selected furanose derivatives, Can. J. Chem., 58 (1980) 1923-1928. 

Rouse dynamics is expected to apply to molecular weights below the critical value where entanglement effects are not yet effective. Experimental data sets for the proton spin-lattice relaxation dispersion [47, 49, 153] are shown in Fig. 27 in comparison to the theoretical frequency dependence predicted by Eq. 64. Very interestingly, the values for the segment fluctuation time Tj fitted to the Ti data coincide with those derived from the Ti minima (see Fig. 14) corrected for the temperature of the field-cycling measurements. That is, the two independent determination methods lead to consistent results. 

Fig. 27a-c. Proton spin-lattice relaxation dispersion under conditions where Rouse dynamics is expected to apply. The theoretical curves have been calculated with the aid of Eq. 64. The validity of this model is restricted to (0 Ts. The positions on the frequency axes where the condition q)Ts=1 apphes are indicated by arrows for the segment fluctuation time Ts fitted to the experimental data. The Tj values are in accord with those derived from the Ti minimum data (see Fig. 14) where applicable, a Polyisobutylene (Mm =4,700 < 15,000), melt at 357 K [49]. b Polydimethylsiloxane (M, =5,200... 

The first observations on the stereochemical dependence of spin-lattice relaxation-rates of carbohydrate molecules, beginning in " 1972, provided a general survey of the nonselective relaxation-rates of the anomeric protons of monosaccharide derivatives, oligosaccharides, and some polysaccharides. 

Nonselective Spin-Lattice Relaxation Rates (s ) for the Anomeric Protons of Monosaccharides and Derivatives"... 

The temperature independence of the Korringa product T T is a better indicator of the metallic character of an NMR signal than the value of its shift. In most metal hydrides, the spin lattice relaxation at room temperature contains important contributions from the diffusive motion of the proton in the hydride lattice. To investigate the Korringa product one must work at relatively low temperatures for the palladium hydrides only values of x > 0.65 are accessible (Fig. 20). For x = 1, 7 T = 46 sK (67), but no values have been given for the shift. Supposing that the total shift 5(1) can be derived from Eq. (21) with the parameters given previously for the palladium black, we obtain 5(1) 51 ppm. From the Ti T value... 

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