Coupling between two nuclei

The dipolar coupling between two nuclei 7,.S is systems containing pairs of... 

In the principal axis frame of the alignment tensor, A, the dipolar coupling between two nuclei, P and Q, as a function of the polar coordinates, 6 and tp, is given by... 

The distortionless enhancement by polarization transfer (DEPT) sequence 253) for the J-coupled heteronuclear spin system (J is 13C- H coupling, approximately 135 to 170 Hz) is shown in Fig. 48. The pulse sequence is based on a resolvable spin-spin coupling between two nuclei, one of them (lH) being the polarization source for the... 

Figure 8.52. Axis system and polar coordinates for the dipolar coupling between two nuclei.

A special case occurs if the solid contains nuclear spin pairs that are sufficiently far apart from each other such that intrapair coupling dominates interpair coupling. In this situation, instead of a featureless broad lineshape, we observe a well-defined powder pattern known as a Pake doublet (Figure 15.15). Since the dipolar coupling between two nuclei... 

The hyperfine splitting constant ay has units of energy and is a characteristic parameter for the interaction of the unpaired electron with a nucleus of type /. It is the analog of the NMR J spin-spin constant describing the magnetic coupling between two nuclei. 

Rotational resonance is an effect whereby the dipolar coupling between two nuclei is restored under MAS by matching the isotropic chemical shift difference between the two spins (expressed in Hz) to an integer multiple of the MAS frequency (p ), i.e.. 

A fundamentally different approach to signal excitation is present in polarization transfer methods. These rely on the existence of a resolvable J coupling between two nuclei, one of which (normally the proton) serves as a polarization source for the other. The earliest of these type of experiments were the SPI (Selective Population Inversion) type (19>) in which low-power selective pulses are applied to a specific X-satellite in the proton spectrum for an X-H system. The resultant population inversion produces an enhanced multiplet in the X spectrum if detection follows the inversion. A basic improvement which removes the need for selective positioning of the proton frequency was the introduction of the INEPT (Insensitive Nucleus Excitation by Polarization Transfer) technique by Morris and Freeman (20). This technique uses strong non-selective pulses and gives general sensitivity enhancement. 

This preliminary discussion of chemical exchange, although it is limited mostly to exchange between two equally populated sites, includes the principles by which N.M.R. spectra can be interpreted in terms of lifetimes of nuclei on these sites. The collapse of spin multiplets due to interruption of spin-spin coupling between two nuclei by an exchange process can be accommodated with only a few extra considerations,... 

In Section 4.7, the first-order splitting patterns arising from coupling between nuclei with / 7 0 are described, but in some circumstances so-called second-order spectra are observed, and these are more complicated to interpret. Second-order spectra can be observed in cases where the coupling between two nuclei is greater than or comparable to their chemical shift difference (in terms of frequency). The effect is to change the... 

The spin-spin scalar coupling between two nuclei has long since become a routine tool in the armament of chemists. This stems partially from the enormous number of empirical relations routinely in use as structure and hybridization probes and partially from the theoretically more tractable relationships which are thought to correctly describe this spin-spin interaction. There are several levels of sophistication commonly in use when discussing the theory of the one-bond metal-phosphorus coupling constant, J(M,P), and this topic, in combination with the question of metal-phosphorus bonding, will be considered first in... 

This says that the corrections to the energy due to spin-spin coupling between two nuclei vary with the product of the m quantum numbers of the spin vectors. 

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