Spin decoupling double-resonance

One-dimensional double-resonance or homonuclear spin-spin decoupling experiments can be used to furnish information about the spin network. However, we have to irradiate each proton signal sequentially and to record a larger number of ID H-NMR spectra if we wish to determine all the coupling interactions. Selective irradiation (saturation) of an individual proton signal is often difficult if there are protons with close chemical shifts. Such information, however, is readily obtainable through a single COSY experiment. 

A wide variety of ID and wD NMR techniques are available. In many applications of ID NMR spectroscopy, the modification of the spin Hamiltonian plays an essential role. Standard techniques are double resonance for spin decoupling, multipulse techniques, pulsed-field gradients, selective pulsing, sample spinning, etc. Manipulation of the Hamiltonian requires an external perturbation of the system, which may either be time-independent or time-dependent. Time-independent... 

The majority of double-resonance solid-state NMR experiments involving spin-1/2 nuclei use transfer of nuclear polarization via dipolar cross polarization (CP) to enhance polarization of the diluted spins S with small gyromagnetic ratio ys and significant longitudinal relaxation time T at the expense of abundant spins I with large y, and short 7 [215]. Typically, CP is used in combination with MAS, to eliminate the line broadening due to CS A, as well as with heteronuclear decoupling. To achieve the / S CP transfer, a (n/2)y pulse is applied at the I spin frequency,... 

The other is double resonance or spin decoupling which effects great simplifications in the spectra. A second radiofrequency field... 

Fig. 11. Single-spin double-resonance experiment for the calibration of irradiation power. The proton line in chloroform is irradiated with the homonuclear decoupler. The strong central feature is at the irradiation frequency, and the separation of the two satellites is...

In practice, spin decoupling experiments are conducted in the following way. First, the spectrum is recorded under normal conditions. Then the spectrum is recorded while a second radiofrequency emitter irradiates at the resonance frequency of the nuclei that are to be decoupled (Fig. 9.22). This double resonance technique is used to identify nuclei which are coupled and which cause interpretation difficulties in the spectrum. 

Figure 9.22—Spin decoupling experiment on butanone. Spectral modification a) by irradiating the CHj group at 2.47 ppm b) by irradiating the CH3 group (of ethyl) at 1.07 ppm, compared to the spectrum shown in Fig. 9.1. For such a simple compound, these experiments are only used to illustrate the principle. On the other hand, a double resonance experiment would be useful to precisely determine the coupling in aspirin (shown in Fig. 9.20).

Spin decoupling or nuclear magnetic double resonance (NMDR) is achieved by irradiating an ensemble of nuclei not only with a radio frequency fl, at resonance with the nuclei to be observed, but additionally with a second alternating field B2 at resonance with the nuclei to be decoupled e.g. H). Decoupling experiments can be carried out to convert homonuclear ( H— JH, 19F —19F) or heteronuclear multiplets (19F—1H,... 

Double Resonance Spin Decoupling and Deuterium Exchange Studies of Cimetidine... 

Both spin decoupling and the NOE are examples of double resonance involving use of an additional channel to irradiate one nucleus at v2 and detect the effect on a different nucleus with a vx pulse. At this point, we... 

Most other homonuclear double-resonance techniques, with names such as spin tickling and selective decoupling, provide information about the arrangement of spin states and the... 

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