Magnetic dipolar coupling

We shall examine magnetic dipolar coupling in more detail in Chapter 7, where we show that when the interacting nuclei are in molecules that are in rapid, random motion, as are most small molecules in solution, this interaction averages almost completely to zero. In this chapter and in Chapter 6, we treat only situations in which magnetic dipolar interactions can be ignored. 

The hyperfine interactions arise from the magnetic dipolar coupling of the triplet electrons with the protons (nuclear spin 1 = 1/2) within the CHj-groups of the sub-... 

Methods based on the electron-electron and electron-nucleus magnetic dipolar coupling are often employed. The point-dipolar approximation discussed in the next section provides a procedure to obtain distances from the observed coupling in pulse or CW-ESR spectra. 

Figure 1 The principal sources of structural data are the NOEs, which give information on the spatial proximity d of protons coupling constants, which give information on dihedral angles < i and residual dipolar couplings, which give information on the relative orientation 0 of a bond vector with respect to the molecule (to the magnetic anisotropy tensor or an alignment tensor). Protons are shown as spheres. The dashed line indicates a coordinate system rigidly attached to the molecule.

It is well-known that the hyperfine interaction for a given nucleus A consists of three contributions (a) the isotropic Fermi contact term, (b) the spin-dipolar interaction, and (c) the spin-orbit correction. One finds for the three parts of the magnetic hyperfine coupling (HFC), the following expressions [3, 9] ... 

X. and Du, J. (2012) Quantum factorization of 143 on a dipolar-coupling nuclear magnetic resonance system. 

DQ coherence between C (,-) and C m and then let the DQ coherence evolve under the influence of the heteronuclear I3C-15N dipole-dipole interaction [181, 182]. The virtue of this design is that it can be easily combined with other resolution enhancement technique such as INADEQUATE [183]. Alternatively, the magnetization of C (,) dephased under the 13C-15N dipolar coupling can be transferred to C (j) for another period of 13C-15N dipolar dephasing [183]. This idea can be combined with the NCOCA experiment so that the superior resolution provided by the C (,-)-N(j+i) correlation could be exploited. The overall efficiency, however, is relatively low due to the use of two polarization-transfer steps, viz. 15N —> 13C and 13C —> 13C [183]. In comparison with the techniques, the advan-... 

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