Chemical shift scale for

Fig. 6. The P-NMR Chemical shift scale for pyridyl phosphane based systems...

Figure 4 Dependence of the 15N principal values of the chemical shift in pyridine with the N-H distance for the pyridine-methanol complex. Note the different chemical shift scales for each shift component, SUj <%2, 3 and < so. The N-H distances are in A and the horizontal scales in the figure are the same for all the shift components.

A closer inspection of the 2D HETCOR cross-sections in the dimension suggests that the isotropic chemical shift of this resonance is correlated with the extent of Al-O-P connectivity, resulting in a tentative chemical shift scale for Q m Ai) species (see Table 1) [83,84]. Replacement of a P by an Al in the second coordination sphere results in upheld shift effects of 10 to 15 ppm. 

We did not observe an isotope-dependent chemical shift under our experimental conditions, if a shift is measured for one of the bromine isotopes, it will be the same, within experimental error, for the other isotope. This is consistent with expected isotope effects on chemical shifts. Based upon our preliminary findings, we suggest that the lUPAC chemical shift scale for both bromine isotopes may be converted to an equivalent scale for solids and that the solid-state bromine standard may be either NaBr(s) or KBr(s). If KBr(s) is used,... 

Figure 3. An 0 chemical shift scale for carbon compounds.

Figure 2, Chemical shift scales for various cadmium-containing compounds are presented here. Data were obtained from the footnote references of the following Chemical Shift Tables. The horizontal scale is cadmium chemical shift in ppm referred to 0,1 M aq.

Figure 2 shows a schematic chemical shift scale for Cd similar to the one previously prepared by Holm et al. (12). Although the recent interest in Cd NMR has expanded the amount of data available, the comments of this early paper still accurately reflect what is known of cadmium chemical shifts. 

The chemical shift ofTMS is defined as 0 5, an absorption that occurs at lower field than tetramethylsilane (TMS) appears to the left of the TMS absorption, has a positive 8 value. The scale is labeled with 8 units or ppm increasing from right to left with 5 = 0 for TMS on the right side of the spectrum. Figure 14.5 shows the chemical shift scale for a series of compounds that have only a single type of hydrogen atom. These hydrogen atoms are chemically equivalent, and therefore, they have the same chemical shift. 

The zero-point on the chemical shift scale is the 8-value for CFC13. 

Solid-state 13C NMR spectra were obtained on a General Electric Omega PSG 400 spectrometer operating at 100.6 MHz for l3C nuclei using a Doty Scientific 5 mm high speed MAS probe. The various NMR experiments performed in this study are shown schematically in Figure 1. The carbon chemical shift scale (11) and 90 degree... 

We assumed that the receptor protons can be subdivided into two classes, PI (and PI ) and P2 (and P2 ), where P2 and P2 stand for protons that experience rf irradiation directly (fast exchange on the chemical shift scale is assumed). The primes indicate protons within the complex. PI and PI stand for all the remaining protons in the receptor in its free and bound states, re-... 

For the majority of organic compounds, the chemical shift range for H covers approximately the range 0-10 ppm (from TMS) and for covers approximately the range 0-220 ppm (from TMS). By convention, the 6 scale runs (with increasing values) from right-to-left for H. 

FIGURE 23. Contour plots of the 2D H-29Si correlation experiments on silica gel obtained with a 22.0 ms contact time, a 3.0 s repetition time and a 4.0 kHz sample spinning rate. The vertical axis represents the proton chemical-shift scale and the horizontal axis the 29Si chemical-shift scale. The spectra above and at the side of the figures are the one-dimensional projections. The 2D spectrum was obtained from 64 individual experiments (a) unwashed silica gel, 80 scans for each individual experiment (b) D2O washed sample, 200 scans for each experiment. Reprinted with permission from Reference 137. Copyright 1988 American Chemical Society... 

There are many analogies in the structural influences on S, P and Se NMR chemical shifts. Wasylishen et al.36 have compared the relative 33S and 77Se chemical shift scales and found that the correspondence is noticeable. For example, the resonances of the hydrides H2S and PH3 lie at the extreme upheld end of the total spectral range. Substitution of a hydrogen atom with a methyl group provokes downfield shifts of 44.7 and 64.5 ppm, respectively. Further substitution of a second hydrogen atom with a methyl causes downfield shifts by 31 and 64.9 ppm, respectively. 

Chemical shift references for calibration of the spectrum scale may be internal or external. An internal chemical shift reference substance is dissolved... 

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