Broadbands spin decoupling

Shaka AJ and Keeler J (1987) Broadband spin decoupling in isotropic liquids. Progress in NMR Spectroscopy 19 47-129. 

In C NMR spectroscopy, three kinds of heteronuclear spin decoupling are used In proton broadband decoupling of C NMR spectra, decoupling is carried out unselectively across a frequency range which encompasses the whole range of the proton shifts. The speetrum then displays up to n singlet signals for the n non-equivalent C atoms of the moleeule. 

We described the nuclear Overhauser effect (NOE) among protons in Section 3.16 we now discuss the het-eronuclear NOE, which results from broadband proton decoupling in 13C NMR spectra (see Figure 4.1b). The net effect of NOE on 13C spectra is the enhancement of peaks whose carbon atoms have attached protons. This enhancement is due to the reversal of spin populations from the predicted Boltzmann distribution. The total amount of enhancement depends on the theoretical maximum and the mode of relaxation. The maximum possible enhancement is equal to one-half the ratio of the nuclei s magnetogyric ratios (y s) while the... 

S, H) spin-spin coupling in the S spectra of dimethyl sulphone, sulpholane 10, and butadiene sulphone 11 was reported for the first time by Hinton.75 Afterward, the values of /( S, H) in dimethyl sulphone and sulpholane 10 have been estimated by comparing the line width value of the 33S resonance lines in 1H-coupled spectra and in spectra obtained under broadband proton decoupling. 

Figure 1. Pulse sequences used to monitor the heteronuclear NOE (bottom panel) and the spin lattice relaxation (top panel). The NOE experiment is a simple extension of the basic pulse sequence introduced by Kay et al. (1989) and utilizes continuous broadband H decoupling during the preparation period to generate the NOE. Two dimensional spectra with and without H decoupling (lightly shaded region) define the NOE. The T, relaxation experiment is a simple extension of the basic pulse sequence introduced by Sklenar et al. (1987). The NOE via H decoupling rather than coherent polarization transfer is used to polarize the carbons. For both the NOE and T, measurement, the proton pulse 0 (or the delay of the corresponding reverse INEPT) is set to the magic angle as described by Palmer et al. (1991). The constant time period, A, is set to minimize cos(n [27i J + 27t Jo,]). When x is set to l/2 Jc then 2A = - 1/2 J( ...

SUSAN Spin decoupling employing ultra-broadband inversion sequences generated via simulated annealing (broadband decoupling sequence) 9.2... 

Figure 5.42. The 2D C, H COSY NMR spectrum of erythromycin in CDCIj as a contour plot beneath the corresponding ID C spin-echo NMR spectrum. The spin-echo spectrum (pulse sequence 90°-(r-I80°-x) -data acquisition) was acquired with broadband proton decoupling during the second period and data accumulation. With x = 8 ms CH2 and C resonances are inverted relative to CHj and CH resonances. The small triangles (A) indicate the two outer lines of the solvent triplet. The contour plot levels are higher than the cross-peaks due to methylene moieties.

In DOUBLE ENDOR (Sect. 4.3) the spin system is simultaneously irradiated with two rf fields. The frequencies of both fields have to be set independently from each other. Generation of rf fields by broadband DOUBLE ENDOR instruments are often strong enough for solid state studies at low temperature. In spin decoupling experiments (Sect. 4.4), however, the amplitude of one of the two fields (namely the decoupling field) should be as large as possible, whereas in studies of multiple quantum transitions ) (Sect. 4.5) two strong rf fields have to be applied. 

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