Pulsed experiments, spin decoupling

Gated decoupling The decoupler is gated during certain pulse NMR experiments, so spin decoupling occurs only when the decoupler is switched on and not when it is switched off used to eliminate either H- C spincoupling or nuclear Overhauser effect in a ID C spectrum, and employed as a standard technique in many other H-NMR experiments, such as APT and y-resolved. 

Inversion pulses are very important because of the wide variety of applications in experiments involving coherence selection and spin decoupling. One of the very first methods for spin inversion was the rapid adiabatic passage introduced by Bloch [18]. 

The second refocusing period again is a spin echo in which chemical shifts are focused by the 180° pulses. The spin roles, however, are reversed in the second set, so that I magnetization is refocused back to two positive peaks for the CH case. The decoupling of protons during carbon acquisition thus does not result in the cancelation of any peaks. The spectrum that is obtained contains decoupled peaks with enhanced intensity. Figure 5-22 compares the various experiments for chloroform. 

In practice, a spin decoupling experiment begins with a record of the spectrum under normal conditions. Next, decoupling is achieved with the aid of a saturation pulse a second spectrum is recorded while irradiating at the resonance frequency of the nucleus (or nuclei) that is (are) to be decoupled (Figure 15.24). This double resonance technique is used to identify nuclei which are coupled and which cause interpretation difficulties in the spectrum, in particular for superimposed signals. 

Using the configuration file ch5721.cfg create the phase sensitive HSQC experiment with decoupling during acquisition The pulse sequence scheme is given below. The template Incorporates the necessary commands for TPPI detection. Save the new sequence with the name myhsqc2n.seq and test the sequence with the current spin system. 

Bennett et al. have given a thorough discussion of SEDRA/RFDR-type experiments in ref. 104, where they covered influences from finite pulses, insufficient proton decoupling, and multi-spin interactions, and introduced a modified version of the basic RFDR sequence with delays of duration kr incorporated between sets of four tt pulses (see Fig. 2Id). This modification recouples weak dipolar coupling interactions only at the conditions n/kyjJt, which avoids the conditions (o A =znu>r) if n/k is not an... 

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