Chemical shift range

Figrue BTl 1.1 shows the range of radiolfequencies where resonances may be expected, between 650 and 140 MHz, when Bq = 14.1 T, i.e. when the H resonance frequency is 600 MHz. There is one bar per stable isotope. Its width is the reported chemical shift range (Bl.11.5) for that isotope, and its height corresponds to the log of the sensitivity at the natural abundance of the isotope, covering about six orders of magnitude. The... 

Just as chemical shifts in H NMR are measured relative to the protons of tetramethylsi lane chemical shifts m NMR are measured relative to the carbons of tetramethylsilane Table 13 3 lists typical chemical shift ranges for some representative types of carbon atoms In general the factors that most affect chemical shifts are... 

Table 2.1. H chemical shift ranges for organic compounds...

The C chemical shift ranges for organic compounds in Table 2.2 show that many carbon-containing functional groups can be identified by the characteristic shift values in the C NMR spectra. 

Table 2.3. Chemical shift ranges for organonitrogen compounds...

In the chemical shift range for alkenes and aromatic and heteroaromatic compounds enol ether fragments (furan, pyrone, isoflavone, 195-200 Hz) ... 

Apart from the A-methyl group, three double-bond equivalents and three multiplets remain in the chemical shift range appropriate for electron rich heteroaromatics, Sh = 6.2 to 6.9. A-Methyl-pyrrole is such a compound. Since in the multiplets at Sh = 6.25 and 6.80 the Jhh coupling of 4.0 Hz is appropriate for pyrrole protons in the 3- and 4-positions, the pyrrole ring is deduced to be substituted in the 2-position. 

First the five protons (integral) of the //NMR spectrum (Sfj = 7.50 - 7.94) in the chemical shift range appropriate for aromatics indicate a monosubstituted benzene ring with typical coupling constants 8.0 Hz for ortho protons, 1.5 Hz for meta protons.). The chemical shift values especially for the protons which are positioned ortho to the substituent Sn = 7.94) reflect a -M effect. Using the CH COLOC plot it can be established from the correlation signal hclS = 66.AI7.94 that it is a benzoyl group A. 

The spectra of Figure 3 illustrate two further points. All the C Is peaks in Figure 3a are of equal intensity because there are an equal number of each type of C atom present. So, when comparing relative intensities of the same atomic core level to get composition data, we do not need to consider the photoionization cross section. Therefore, Figure 3c immediately reveals that there is four times as much elemental Si present as Si02 in the Si 2p spectrum. The second point is that the chemical shift range is poor compared to the widths of the peaks, especially for the solids in Figures 3b and 3c. Thus, not all chemically inequivalent atoms can be distin-... 

Difluommethyl moieties have a weU-defmed chemical shift range from -110 to -129 ppm and couphngs of approximately 57 Hz ( 7hf) 17 Hz Fluorme... 

The rehability of these analytical methods may be questionable when chemical shift differences of derivatives are of the same magnitude as variations encountered from solvent, concentration, and temperature influences. Reported fluorine chemical shift ranges for tnfluoroacetylated alcohols (1 ppm), p-fluorobenzoylated sterols (1 ppm), and p-fluorobenzoylated ammo acids (0.5 ppm) are quite narrow, and correct interpretation of the fluonne NMR spectra of these denvatized mixmres requires strict adherence to standardized sampling procedure and NMR parameters. 

Another 2D homonuclear shift-correlation experiment that provides the coupling information in a different format is known as SECSY (spin-echo correlation spectroscopy). It is of particular use when the coupled nuclei lie in a narrow chemical shift range and nuclei with large chemical shift differences are not coupled to one another. The experiment differs... 

The chemical shifts of the P—H group have been tabulated for 150 compounds. Like many other heteroatom-bound protons, the chemical shift range is large (r 0 —12 p.p.m.). In this case shielding of the proton increases with decrease in co-ordination number at phosphorus. The... 

A broad chemical shift range of 250 ppm (i.e. about 20 times greater than that of ll NMR), which greatly facilitates resolution of individual resonances in complex mixtures. 

Natural-abundance, 13C-n.m.r. spectroscopy is not a technique that may be applicable to all systems. It does have a few drawbacks, despite its overall, positive appeal. The relatively low gyromagnetic ratio of carbon-13, its low sensitivity, and its low natural abundance do present some handicaps.33 However, these factors are outweighed by the large chemical-shift range for carbon atoms in glycoproteins (—200 p.p.m.) and the fact that glycoproteins contain a multitude of carbon atoms... 

The most distinctive features of the H and 13C n.m.r. spectra of bicyclic peroxides are provided by their bridgehead nuclei. An analysis of the data on over thirty compounds indicates that the characteristic chemical shift ranges are 5 3.7-4.8 for bridgehead protons and 8 72-89 for bridgehead carbons. 

In all cases the oxidation state of phosphorus is five, and the chemical shift range observed is only about 12 ppm. Note that the two phosphorus atoms attached to the methine carbon are non-equivalent because they are chemically different (phosphonate and phosphine oxide). We can expect the coupling between aP and bP to be large, as they are separated by two bonds, while that of aP to bP or CP will be small (coupling over five bonds). 

The total chemical shift range is close to 1000 ppm, whereby amines and nitroso compounds lie at opposite ends of this range. 

The total chemical shift range is over 1000 ppm, so that although fluorine-element coupling constants are relatively large the spectra are generally relatively easy to interpret. 

As far as NMR is concerned, the spin-Vi nucleus silicon-29 has a natural abundance of 4.7%. The chemical shift range is around 600 ppm, and the shift of TMS is the zero-point. 

The natural abundance of selenium-77 is 7.58%. The chemical shift of dimethyl selenide is set equal to 0 ppm. The total chemical shift range is around 2200 ppm, organoselenium compounds covering almost the whole range. Figure 41 shows the spectrum of H2Se03 in D20, the linewidth being only... 

Tin is an unusual element in that it has three magnetically active isotopes, all spin-Vi. However, tin-115 has a natural abundance of only 0.35%, and is never studied. The other two, tin-117 and tin-119, occur in similar amounts (7.61 and 8.58% respectively). Spectra of the latter are normally recorded, as it is about 25% stronger. Tetramethyltin is taken as the zero-point, and the total chemical shift range is about 3000 ppm. 

Platinum-195 is the only magnetically active isotope of platinum, the natural abundance being 33.8%. The shift of a saturated solution of K2PtCl6 is in D20 defined as zero ppm. The total chemical shift range is huge, about 13,000 ppm (from -6000 to +7000 ppm ). 

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