Dipolar Dephasing Interrupted Decoupling

Fig. 47. 15 MHz 13C MAS NMR spectrum of cured furfuryl alcohol resin a. The spectrum of the same resin obtained with dipolar dephasing (100 ps interrupted decoupling) b (reprinted from Ref.2341 with permission)...

The pulse sequences used for this purpose are known as interrupted decoupling (Gerasimowicz et al. 1984, Haw et al. 1984, Barron et al. 1985, Maciel et al. 1985), delayed decoupling (Manders 1987) or dipolar dephasing (Hatcher 1987). All involve an interval, t inserted in the pulse sequence between the end of the contact time and the beginning of data acquisition as shown in Fig. 4.5.2. Both nC and proton RF transmitters are switched off for the duration of t and strong static dipolar interactions between, 3C... 

Solid-state C NMR spectra of oil shales, obtained by CP/MAS with high-power decoupling are broad because of the multitude of resonances from the different carbon types found in these complex materials. A number of af roaches have been taken to improve the resolution of solid-state NMR of fi il fuels. Such tedmiques include variable temperature studies, variable frequency studies, mathematical enhancements and deconvolution techniques, and relaxation rate methods. The most popular method of enhancing solid-state NMR spectra is a relaxation rate method called dipolar dephasing (DD), which is sometimes referred to as interrupted decoupling. The exploitation of relaxation methods in CP NMR of fossil fuels has been reviewed elsewhere. ... 

Lower the "interrupted-decoupling spectrum of the same material. Only i3C signals in the mobile polyether soft segment and the non-protonated i3C resonances in the hard segment survive the 50 ps dipolar dephasing delay. 

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