Direct dipolar couplings

In solids, the averaging due to fast movement will not occur, or even if it does, occurs partially then, the effects of direct dipolar couplings can be observed [72,73], The direct magnetic dipolar interaction between nuclear spins causes a nucleus with spin projection, ml5 to produce a magnetic field in the z-axis, Bimc, at a distance, R, given by the following expression [12]... 

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... 

Homonuclear Correlations via direct (dipolar) couplings, D-HOMCOR... 

Direct dipolar coupling occurs in solids the definition of the coupling constant is DAB... 

In normal liquids, most molecules move isotropically and dipolar couplings are averaged to 0. In static solids and in liquid crystals, molecular motion is non-existent or anisotropic and dipolar couplings are observed. In solids, dipolar couplings are obscured by chemical shift anisotropy but in liquid crystals, they are observed and can be large, up to the kHz range [423], The size of the direct dipolar coupling (Dy) between nuclei i and j is ... 

Anisotropy of the Spin-Spin Coupling Tensor. - In NMR experiments performed in anisotropic liquid crystal (LC) phases or in the solid state, the anisotric part of an indirect nuclear spin-spin coupling tensor J appears combined with the direct dipolar coupling D. The NMR spin Hamiltonian appropriate for spin 1/2 nuclei in molecules partially oriented in uniaxial LC solvents can be written in the high field approximation as... 

It is the interpretation of the parameters Dq that yields information on molecular geometry. The direct dipolar coupling parameter of nuclei i and / of a molecule can be written as an average over all molecular motions, including the vibrations and tumbling of the molecule... 

The direct dipolar coupling (first term in the Eqn. (9)) can easily be calculated as it does not depend on the electronic structure. 

When broad band decoupling is used to simply the spectrum, it is noted that peak areas increase more than is expected from elimination of the peak splitting. This is the NOE. Direct dipolar coupling between a saturated nucleus and an unsaturated nucleus results... 

Figure 4.2 Energy levels in a two-qubit NMR system (a) two 7-coupled spin 1/2 system. Direct dipolar coupled systems in the weak coupling limit have similar energy configuration replacing the 7 coupling by the dipolar coupling constant, (b) Quadrupolar spin 3/2 system. The three allowed transitions labeled 01, 12, and 23 are indicated.

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