Heteronuclear spin decoupling

When we discussed heteronuclear C-H spin coupling (Section 8.6.1), we noted that all the C spectra presented in Chapters 5 and 7 had been proton decoupled, because in the absence of such decoupling the spectra would have been considerably more complex. Now we are ready to see how the effects of C-H spin coupling can be erased when acquiring a C spectrum. 

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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. 

In C NMR spectroscopy, three kinds of heteronuclear spin decoupling are used. 

If no chemical-shift differences existed, an abundant low-y spin system in the absence of further spins (or in the presence of efficient heteronuclear spin decoupling) would behave in the same way as an abundant high-y spin system. In practice, however, the chemical-shift differences tend to be comparable to and often larger than the dipolar couplings and they must be included in the system Hamiltonian... 

Full chemical-shift and coupling-constant data for OPF2H, SPF2H, and SePF2H have been obtained from and F n.m.r. measurements using heteronuclear spin-decoupling techniques. ... 

M. Ernst, Heteronuclear spin decoupling in sohd-state NMR under magjc-angle sample spinning, J. Magn. Reson. 162 (2003) 1—34. 

In the case of heteronuclear spin decoupling the decoupled and observed nuclei are of different chemical types. The experiments are illustrated with examples in which protons are decoupled and the effect observed on the C spectrum. However the methodologies are equally applicable to other heteronuclear spin systems. 

P. K. Madhu, Heteronuclear Spin Decoupling in Solid-State Nuclear Magnetic Resonance Overview and Oudook, Israel J. Chem., 2014, 54, 25. 

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