Nuclear magnetic resonance spin connectivity

This hyperfine broadening of resonant absorption is consistent with theoretical investigations according to which the main dephasing mechanism of magnetic molecules is connected to nuclear spins [52, 72-75]. 

As we shall see, each of these two terms, one for each nucleus, describes a second-rank scalar interaction between the electric field gradient at each nucleus and the nuclear quadrupole moment. De Santis, Lurio, Miller and Freund [44] included two other terms which involve the nuclear spins. One is the direct dipolar coupling of the 14N nuclear magnetic moments, an interaction which we discussed earlier in connection with the magnetic resonance spectrum of D2 its matrix elements were given in equation (8.33). The other is the nuclear spin-rotation interaction, also discussed in connection with H2 and its deuterium isotopes. It is represented by the term... 

The use of NMR spectroscopy to characterize diamagnetic transition metal and posttransition metal complexes has increased tremendously in the past decade (111, 129). Mercury has two NMR-active isotopes, Hg (natural abundance = 13.22%) and (natural abundance = 16.84%). The former is quadrupolar (nuclear spin, / = ), and consequently, much more difficult to observe, due to line broadening. The latter, on the other hand, is one of approximately 20 nuclides in the periodic table with the preferred spin I = i. Its receptivity, a measure of relative signal strength, is five times that of C for comparison, " Cd, the most widely studied of the posttransition nuclei, has a receptivity of only 8 relative to C. Magnetic resonance frequencies are intimately connected with the quantity and dis-... 

TTie TOCSY 2D NMR experiment correlates all protons of a spin system, not just those directly connected via three chemical bonds. For the protein example, the alpha proton, Ft , and all the other protons are able to transfer magnetization to the beta, gamma, delta, and epsilon protons if they are connected by a continuous chain—that is, the continuous chain of protons in the side chains of the individual amino acids making up the protein. The COSY and TOCSY experiments are used to build so-called spin systems—that is, a list of resonances of the chemical shift of the peptide main chain proton, the alpha proton(s), and all other protons from each aa side chain. Which chemical shifts correspond to which nuclei in the spin system is determined by the conventional correlation spectroscopy connectivities and the fact that different types of protons have characteristic chemical shifts. To connect the different spin systems in a sequential order, the nuclear Overhauser effect spectroscopy... 

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