High-powered proton-decoupling effect

Fig. 4.32 Demonstration of the cumulative effects of techniques employed in C CP/MAS SSNMR spectroscopy on a sample of dideoxyinosine. (a) High-power proton decoupling combined with magic-angle spinning (MAS) and cross polarization (CP) (b) high-power proton decoupling and MAS at 5 kHz (c) high-power proton decoupling only and (d) conventional solution phase techniques. (From Bugay 1993, as modified by Byrn et al. 1999.)...

One consequence of high-power proton decoupling during observation of F spectra is that resonance frequencies will be affected by the Bloch-Siegert effect [11]. This has been thoroughly investigated by Vierkotter [12] for some nonpolymeric fluorinated compounds, and has been observed for polymeric systems [13]. The shift (expressed as a fraction) is given by ... 

We report here the application of the solid state carbon-13 1 1R with cross-polarization (CP), high power proton decoupling, and magic-angle sample spinning (MAS) to study the curing of epoxy resins. On the basis of our preliminary studies, we show here the application of solid state carbon-13 NMR spectroscopic data to determine some of the Important parameters such as the gelation point and effective functionality of the epoxy monomers. 

Fig. 8.3. The effect of high-powered proton decoupling is shown for the C spectra at — 180°C of the central carbon of the im-butyl cation prepared from [2- C]2-chloro-2-methylpropane and SbFs. Spectrum a was obtained without decoupling and spectrum b was obtained with strong (43 kHz) H and decoupling. (Reproduced from Ref [10]. 1982 American Chemical Society.)...

The spin-lattice relaxation time for in solids is very long (several minutes). Since the nuclei have to relax before another excitation pulse can be sent, this requires hours of instrument time in order to collect a spectrum of reasonable intensity. A pulse technique called cross-polarization can be used to reduce this effect by having the protons interact with the carbon nuclei, causing them to relax more rapidly. FTNMR systems for sohd samples include the hardware and software to produce narrow line spectra from solid samples in a reasonable amount of time using high-power dipolar decoupling, MAS, and cross-polarization. 

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