Natural abundance sensitivity

Nuclei Spin Natural abundance Sensitivity Relative Absolute Range Gyromagnetic ratio Frequency ... 

Isotope NMR Frequency, 10 Kgauss Field, MHz Natural Abundance, % Sensitivity Constant Field) Relative tolH = 1 Spin, h/2% Quad-rupole Moment, e Cn... 

Nucleus Spin Resonant frequency (MHz) Natural abundance(%) Sensitivity wrt H Quadrupole moment (10 m A)... 

Nucleus Spin Gyromagnetic ratio (rads T"1) Larmor frequency, (MHz) at 3.0T Natural abundance (%) Sensitivity relative to H Chemical shift range (ppm)... 

Isotope Spin Natural abundance Sensitivity NMR frequency (MHz) at a field (T) of ... 

The first ever reported correlation NMR spectra performed with the natural abundance sensitivity of Si and presenting both types of borate units have thus been obtained by the D-HMQC technique. New insights onto the sdicate medium-range order and onto the B—Si mixing extent have been derived. Added to other correlation NMR techniques, the complete set of data gives unprecedented high detailed vision of the mixed structure of sodium boro-sdicate glass structure [67]. 

Atomic weight/ element Spin Natural abundance (%) Sensitivity (versus Quadrupole moment (10-2 jy[2) Gyromagnetic ratio (10 rad T-l sec-l) Resonance frequency ( H tms 100 MHz)... 

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... 

Nuclide Natural abundance, % Spin I Sensitivity at constant field relative to NMR frequency for a 1-kG field, Mffz Magnetic moment J-T-1 Electric quadrupole moment Q, 10 m ... 

Carbon-13 nmr. Carbon-13 [14762-74-4] nmr (1,2,11) has been available routinely since the invention of the pulsed ft/nmr spectrometer in the early 1970s. The difficulties of studying carbon by nmr methods is that the most abundant isotope, has a spin, /, of 0, and thus cannot be observed by nmr. However, has 7 = 1/2 and spin properties similar to H. The natural abundance of is only 1.1% of the total carbon the magnetogyric ratio of is 0.25 that of H. Together, these effects make the nucleus ca 1/5700 times as sensitive as H. The interpretation of experiments involves measurements of chemical shifts, integrations, andy-coupling information however, these last two are harder to determine accurately and are less important to identification of connectivity than in H nmr. 

Other Nuclei. Although most nmr experiments continue to involve H, or both, many other nuclei may also be utilized Several factors, including the value of I for the nucleus, the magnitude of the quadmpolar moment, the natural abundance and magnetogyric ratio of the isotope, or the possibihty of preparing enriched samples, need to be considered. The product of the isotopic parameters can be compared to the corresponding value for providing a measure of relative sensitivity or receptivity. Table 1 summarizes these factors for a number of isotopes. More complete information may... 

Although the natural abundance of nitrogen-15 [14390-96-6] leads to lower sensitivity than for carbon-13, this nucleus has attracted considerable interest in the area of polypeptide and protein stmcture deterrnination. Uniform enrichment of is achieved by growing protein synthesi2ing cells in media where is the only nitrogen source. reverse shift correlation via double quantum coherence permits the... 

Isotope Natural abundance (%) Nuclear spin Electric quadrupole moment NMR frequency fora 23.5 kO field (MHz) Relative sensitivity... 

With improvements in Instrument sensitivity and the use of techniques such as enhancement by polarization transfer (INEPT), it can be expected that natural abundance N NMR spectra will become increasingly Important in heterocyclic chemistry. The chemical shifts given in Table 10 illustrate the large dispersion available in N NMR, without the line broadening associated with N NMR spectra. 

In some ways, it s surprising that carbon NMR is even possible. After all, 12Q the most abundant carbon isotope, has no nuclear spin and can t be seen b> NMR. Carbon-13 is the only naturally occurring carbon isotope with a nucleai spin, but its natural abundance is only 1.1%. Thus, only about 1 of ever) 100 carbons in an organic sample is observable by NMR. The problem of low abundance has been overcome, however, by the use of signal averaging anc Fourier-transfonn NMR (FT-NMR). Signal averaging increases instrument sensitivity, and FT-NMR increases instrument speed. 

The most convenient technique used to study organotin(IV) derivatives in solution and in solid state is Sn NMR spectroscopy. The Sn nucleus has a spin of 1 /2 and a natural abundance of 8.7% looking only at the isotopic abundance, it is about 25.5 times more sensitive than The isotope Sn is slightly less sensitive (natural abundance 7.7%) but it has not been used as much. Both nuclei have negative gyromagnetic ratios, and, as a consequence, the nuclear Overhauser enhancements are negative. Some examples of the applications of this method are mentioned later, in different sections. 

Figure 4.18 shows the positive SIMS spectrum of a silica-supported zirconium oxide catalyst precursor, freshly prepared by a condensation reaction between zirconium ethoxide and the hydroxyl groups of the support. Note the simultaneous occurrence of single ions (H", SR, 7.r ) and molecular ions (SiO, SiOH, ZrO, Zr02 ). Also, the isotope pattern of zirconium is clearly visible. Isotopes are important in the identification of peaks, because all peak intensity ratios must agree with the natural abundances. In addition to the peaks expected from zirconia on silica mounted on an indium foil, the spectrum of Fig. 4.18 also contains peaks from Na, K, and Ca. This is typical for SIMS Sensitivities vary over several orders of magnitude and elements such as the alkalis are detected when present in trace amounts. 

Nucleus Natural abundance (%) Relative sensitivity Ease of use... 

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... 

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