Atomic gyromagnetic ratio

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 sensitivity of an atomic nucleus in the NMR experiment is related to its gyromagnetic ratio y. It determines the energy difference AE between the precession states in a magnetic field of flux density B0 (Figs. 2.1 and 2.35) ... 

Here, yH, yc and Wh, o>c are the gyromagnetic ratios and Larmor frequencies of the carbon and proton nuclei, respectively h (=/i/27r) is Planck s constant rc.H is the C—H bond length noted earlier and N is the number of protons directly attached to the carbon atom under consideration. The n.O.e. value in Eq. 14 depends neither on the number of protons nor on the C—H distance, in contrast to the other two parameters. This means that the T, and T2 values of the carbon nuclei are affected by neighboring intramolecular protons. The shortest distances (1.08-1.09 A) involve directly attached protons, making them the main contributors to the relaxation of a carbon nucleus. 

Most polymer characterization is accomplished with H and NMR although N, F, Si, and NMR are also routinely used. H NMR is most commonly used because it is present in most chemical structures, has 100% natural abundance and a high gyromagnetic ratio, making it the most sensitive of all the NMR observable nuclei to detect. Moreover, because of its fast relaxation and the ability to extract information from spin-spin coupling constants, H NMR is one of the most useful techniques for determining chemical structure. However, because of its small chemical shift range (only 10 ppm) and the complexity of each proton resonance, severe peak overlap occurs for H atoms situated in similar chemical environments. 

Brunner, Pines and coworkers reported on the enhancement of NMR signals in solid Cgo and C70 using a laser-polarized xenon. NMR signals emanating from surface nuclei of solids may be enhanced by the transfer of spin polarization from laser-polarized noble gases via SPINOE (spin polarization induced nuclear Overhauser effect). The paper describes experiments in which the spin polarization is transferred under MAS from laser-polarized - Xe to a nuclear spin with a low gyromagnetic ratio in the fullerenes Ceo and C70, which are polycrystalline materials with a low surface area. In C70, a different degree of enhancement of the NMR spectrum is observed for the different atomic sites in the molecule. 

Moreover, for covalently linked pairs of atoms, the unique axis of the tensor is parallel to this covalent bond direction and the magnitude of the dipolar interaction can be calculated directly from a knowledge of the gyromagnetic ratios, Tn and yx and the internuclear separation. 

The ratio of the magnetic moment of a system to the angular momentum of that system. The gyromagnetic ratio is a useful quantity in the theory of electrons and atomic nuclei. 

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