Deuterium spectrum

Lowering the temperature has a similar effect on the deuterium spectra as does increased loadings. In Figure 3, spectra for benzene-d6/(Na)X at 0.7 molecules/supercage over the temperature range 298 to 133 K are shown. It is observed that both benzene species are detected simultaneously between 228 and 188 K. Below this temperature the oriented benzene species becomes the predominant form. A similar situation occurs for polycrystalline benzene-dg in which two quadrupole patterns, one static and the other motionally narrowed due to C rotation, are observed to coexist at temperatures between 110 and 130 K (7). This behavior has been attributed to sample imperfections (8) which give rise to a narrow distribution in correlation times for reorientation about the hexad axis. For benzene in (Na)X and (Cs,Na)X such imperfections may result from the ion/benzene interaction, and a nonuniform distribution of benzene molecules and ions within the zeolite. These factors may also be responsible for producing the individual species. However, from the NMR spectra it is not possible to... 

While the deuterium spectra of benzaldehydes from different sources do not appear (upon visual inspection) to have significant differences from one another, other than some variation in intensity, the deuterium distribution of benzaldehyde does form clusters on a principal component analysis plot. Benzaldehyde products from the same source have similar deuterium distributions and are therefore close to each otlier on the plot (Figure 1). Thus, the origin of benzaldehyde can be differentiated based on site-specific deuterium distribution. Products outside of the clusters of knoivn samples are normally considered as originating from an unknown source or as a mixture of benzaldehyde from different known sources. 

Another nucleus of considerable analytical potential is deuterium, whose observation at natural abundance has been demonstrated earlier (9) but whose practicality has so far been severely limited due to its low NMR receptivity and also because of its more than six times smaller chemical shift range relative to the proton. These limitations are largely overcome at high magnetic field as illustrated by the natural-abundance deuterium spectra of camphor In Figure 8. 

Further information may be extracted from the analysis of the fine structure of proton - coupled high resolution deuterium spectra. Thus, the proton-coupled deuterium spectrum of the methyl group of propene appears as a doublet of doublets (see inset to Figure 5), indicating that the position must be doubly deuterated. 

FIGURE 19.16 Chain mobility as shown in the deuterium spectra of amorphous regions of linear polyethylene at various temperatures. [Source Speiss (1985). By permission of Springer-Verlag.]... 

The acquisition of such wide-line signals is more demanding than for high-resolution spectra because the receiver must be turned on immediately following the pulse and the data must be acquired very quickly. For this reason, deuterium spectra are typically acquired using the (90°-T -90°-T -acquire) quadrupolar echo-pulse sequence in which the data are acquired as an echo so the receiver is not turned on immediately after the pulse. 

R48. NMR of membranes Jacobs, R. E. Oldfield, E. Prog. NMR Spect. 1981, 14, 113-136. Mainly focuses on phosphorus and deuterium spectra. 172 references. Includes introductory theory. 

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