Dipolar broadening homonuclear

Hydrogen. - The H nucleus has been traditionally the most important for n.m.r. investigations. It has spin-, natural abundance of practically 100%, high gyromagnetic ratio, and relatively short relaxation time, and consequently is the most sensitive of all nuclei. Its chemical shift range is however small (about lOp.p.m.), and in the field of solid-state n.m.r., where homonuclear dipolar broadening is a severe problem for 100%-abundant nuclei, the width of the lines frequently, but by no means always, tends to obscure the important chemical shift information which we have come to expect from 13 C and 29Si n.m.r. 

Gerstein, B.C., Pembleton, R.G., Wilson, R.C., and Ryan, L.M. 1977. High resolution NMR in randomly oriented sohds with homonuclear dipolar broadening Combined multiple pulse NMR and magic angle spinning. J. Chem. Phys. 66 361-362. 

Homonuclear J coupling between abundant spins, such as F- F, or F- H can produce more intricate patterns, which are often obscured by residual dipolar broadening in spectra of polymer solutions (Sec. II.B). In solid-state NMR spectra, scalar couplings are not detected... 

The carbon-proton dipolar interaction and the chemical shift anisotropies broaden the lines in solid state 13C NMR spectra. The major effect arises from the dipolar coupling of the carbon nuclei with neighboring protons homonuclear dipolar couplings between two adjacent 13C nuclei are neglegible because of their low natural abundance. The large magnitude of dipolar 13C— H coupling (up to 40 kHz) results in broad and structureless proton-coupled 13C NMR absorptions. 

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