Proton-flip experiment

Fig. 31. Stacked plot of the heteronuclear two-dimensional J-resolved spectrum of cured, carbon black filled, natural rubber. The proton flip experiment was used with high-power proton decoupling during the detection time. The experiment was performed with the sample spinning at the magic angle (reprinted from Ref. 1911 with permission)...

For either experiment we can consider that irradiated protons to flip back and forth between their two spin-states so rapidly that they no longer couple with other protons in the same molecule. An alternative rationale can be couched in terms of the decoupling field equalizing the populations of the two energy levels of the irradiated protons, which is qualitatively equivalent to saturating that resonance. (Although neither of these two models is strictly correct, they do at least provide a simple rationale for the N.M.D.R. experiment.)... 

Fig. 14.4 Pulse sequences used for the experiments described in this chapter. A [ N HJ-HSQC with water flip back and PFGs. The shaped pulse on the proton channel is a sine-shaped, 1.5 ms soft pulse all other pulses are hard pulses. Gradients are applied as square or sine-shaped pulses. The sign of the last gradient is reversed for anti-echo selection together with the sign of phase 6. B CPMG sequence. C bpPFGLED sequence. The delay T denotes the diffusion delay. Typically, r is set to 1 ms, T to 50-100 ms and Te to 1.2 ms.

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