Proton spin decoupling

It now appears that such difficulties can largely be overcome by the application of proton-proton spin-decoupling and especially by means of the very high resolution now available in spectrometers of the superconducting solenoid type (see below). 

Before the advent of 2D NMR spectroscopy, the classical procedure for determining proton-proton connectivities was by homonuclear proton spin decoupling experiments. Such experiments can still serve to determine some H/ H connectivities in simple molecules. 

A solid-state 90 MHz Fourier Transform Instrument with a 96 MHz channel for 3H observation, proton-spin decoupling... 

Take a moment to look back at the 250- and 400-MHz H spectra of toluene in Figures 5.3 and 5.4. Do you recall that there were more lines (at least six) for the aromatic hydrogens than the three we predicted from symmetry considerations And do you recall from our discussions in Chapters 5 and 7 that all of the l3C spectra involved a technique called proton spin decoupling These phenomena are related. 

One problem with the basie INEPT sequence described above is that it precludes the applieation of proton spin decoupling during the acquisition of the X-spin FID. Since this removes the J-splitting it will cause the antiphase... 

By use of both deuterated compounds and proton-spin decoupling, the resonance spectrum of purine has been analysed. A correlation of the data with the theoretical estimates of charge distribution was found in purine, although a polarization effects may be important especially for the carbon atoms 2 and 8 centred between two nitrogen atoms (IS). 

Off-Resonance Decoupling Proton spin decoupling produces spectra that are very simple, but some valuable information is lost in the process. Off-resonance decoufdii simplifies the spectrum but allows some of the splitting information to be retamed (Figure 13-44). With off-resonance decoupling, the nuclei are split only... 

NMR can, in principle, provide complementary information on motional processes in liquid crystals. The dipole-dipole interaction between a C-H pair and the quadrupolar interaction when the proton is replaced with a deuteron share the same principal interaction axis. In the case where the carbon is not directly bonded to a proton, there is still dipole-dipole relaxation by nearby protons, but it is also necessary to include an additional relaxation mechanism, the modulation of the chemical shift anisotropy. Proton spin decoupling is necessary to give well-resolved chemically shifted lines in the mesophase of liquid crystals. Furthermore, it is not practical to determine individual spectral density parameters from measured relaxation rates. Proton-proton dipolar interactions may not be ignored even when observation is exclusively confined to the resonant spin [5.31]. This is because proton relaxation causes population flow among the proton spin levels through dipolar (or scalar) coupling. As a consequence, cross-... 

This multiplet structure weakens the signal for the spectra and, in the case of many resonances, complicates the spectra beyond recognition. For C solution NMR spectroscopy it is desirable to eliminate the multiplet fine structure arising from the J coupling of the carbons to the protons. Spin decoupling causes the vectors of a multiplet to be static in the rotating frame because their Larmor frequencies become... 

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