Gyromagnetic ratio,

Sometimes called the gyromagnetic ratio. For a free electron = 2-003. 

The proportionahty constant y is called the gyromagnetic ratio which is a function of the magnitude of the nuclear magnetic moment. Therefore each isotope having a net nuclear spia possesses a unique y. The y of some biologically relevant nuclei can be found ia Table 3. 

Table 3. Gyromagnetic Ratios for Biologically Relevant Nuclei ...

Figure 8 Effects of spin diffusion. The NOE between two protons (indicated by the solid line) may be altered by the presence of alternative pathways for the magnetization (dashed lines). The size of the NOE can be calculated for a structure from the experimental mixing time, and the complete relaxation matrix, (Ry), which is a function of all mterproton distances d j and functions describing the motion of the protons, y is the gyromagnetic ratio of the proton, ti is the Planck constant, t is the rotational correlation time, and O) is the Larmor frequency of the proton m the magnetic field. The expression for (Rjj) is an approximation assuming an internally rigid molecule.

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. 

While the rate of change of dipolar interaction depends on t its magnitude depends only on the internuclear distance and is independent of t,. Thus the dipole-dipole relaxation depends on the molecular correlation time T the internuclear distance r, and the gyromagnetic ratios of the two nuclei, y and js -... 

In the case of proton-proton interactions, both nuclei S and /will have the same gyromagnetic ratios, and an implication of the Equation (4) then is that there is an upper limit of 50% on the nOe obtainable, whatever the distance between nuclei S and I. This means that the observation of an nOe between two nuclei does not necessarily mean they are spatially close to one another, and nOe results must therefore be interpreted with caution. Similarly, as will be seen later, the absence of nOe between two nuclei does not necessarily mean they are far apart. In the case of heteronuclear nOe, since the gyromagnetic ratio of proton (yv) is four times the gyromagnetic ratio of carbon y,), js/ jt can be four times greater than that obtainable in homonuclear nOe. 

As stated earlier, since tt]/ = yff2yr and since the gyromagnetic ratio of proton is about fourfold greater than that of carbon, then if C is observed and H is irradiated (expressed as C H ), at the extreme narrowing limit Ti, = 198.8% i.e., the C signal appears with a threefold enhancement of intensity due to the nOe effect. This is a very useful feature. For instance, in noise-decoupled C spectra in which C-H couplings are removed, the C signals appear with enhanced intensities due to nOe effects. 

Sauer et al. [185] determined the gyromagnetic ratio g(9/2)/g(7/2) and the magnetic moment of the 6.2 keV level in Ta in two ways, (1) from the Zeeman split velocity spectrum of a metal source in a longitudinal field versus a Ta... 

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