Broadening of NMR spectra

The averaging effects of exchange apply to any dynamic process that takes place in a molecule (or between molecules). However, many processes occur at rates that are too fast or too slow to give rise to visible broadening of NMR spectra. The NMR time-scale happens to coincide with the rates of a number of common chemical processes that give rise to variation of the appearance of NMR spectra with temperature and these include ... 

Andrew, E.R. Eades, R.G. Removal of Dipolar Broadening of NMR Spectra of Solids by Specimen Rotation, Nature 183, 1802 (1959). 

It has been observed that line broadening of NMR spectra of solid powders arises jointly from static... 

Dipolar interactions, responsible for the broadening of NMR signals, can, in principle, be eliminated in the case of an abundant nucleus such as the proton, but the small range of proton chemical shifts makes the use limited. In the case of dilute nuclei, spectra of fair resolution are readily obtained. The magnetic interaction for such a nucleus is given by... 

An observation of spin-spin coupling between proton and fluorine by 19F NMR and/or 1H NMR would be the most direct and convincing evidence. However, there has been only one report on such H—F spin-spin couplings in the compound 3, and only a few reports described broadening of the spectra. Meanwhile, the interaction of metal with organic fluorine (M- -F—C) with spin-spin coupling has often been reported (Scheme 4.2) [10,17-19]. Dynamic interaction of organic fluorine with a metal species has been summarized well in Ref. [17],... 

The restricted mobilities of the hydrophobic segments and the dynamic profile are also reflected in the shape of NMR-spectra of vinylic polysoaps in aqueous solution. The signals of protons in the proximity of the polymer backbone are strongly broadened [193, 258, 303, 355] or virtually invisible [39, 227] (Fig. 31). This effect decreases with decreasing density of the hydrophobic tails [193, 303, 355, 357] and with decreasing molecular weight. 

While high-power proton ( H) decoupling removes the dipolar line-broadening, the NMR spectra of solids are stiU much broader than those of corresponding solution spectra. This residual broadening is due to chemical... 

---