Nuclear magnetic resonance spectrum scalar coupling

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 nuclear Overhauser effect is used to measure distances between nuclei. It is a relaxation effect that, like a chemical reaction, is incoherent in nature as opposed to the scalar coupling that is coherent and is detected as a frequency splitting of resonances in the spectrum. Relaxation can be best viewed at as the flow of population between different states as it would occur in a chemical reaction where one molecule is transformed, e.g., by a reaction of zero-order into a second molecule. The same is true for the NOE where magnetization of spin A by a zero-order reaction is transferred to mag-... 

The NMR spectra presented in Fig. 20.9 [11] for the same PP samples whose H NMR spectra appear in Fig. 20.8 make the superior microstructural sensitivity of NMR plainly evident. While resonances are spread over an 30 ppm range, aU H resonances observed for PPs are within < 1 ppm of each other. In addition, the absence of homonuclear ( C- C) and the easy removal of hetero-nuclear ( C- H) scalar couplings further simplify the spectra. Both of these advantages result in the kind of microstructural sensitivity seen in the methyl carbon region of the PP spectra note that in atactic PP sample all ten possible pentad stereosequences mmmm, rrrr, mmrm, etc.) are distinctly observed. (Also see in Fig. 20.10 an expansion of the methyl region of the atactic PP spectrum observed at a higher magnetic field, which we will subsequently discuss.)... 

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