Friday, May 30, 2008
1H with 19F Decoupling
The proton NMR spectra of compounds containing fluorine often show 1H - 19F J coupling. This can of course provide useful information but is also sometimes seen as an unwanted complication. In such cases, it can be removed by 19F decoupling. An example of this is shown in the figure below. Depending on the NMR equipment used, observing 1H [19F] spectra may be more difficult than for example observing protons with 31P, 13C, 11B or even 27Al decoupling. The difficulty arises because the frequencies of 1H and 19F are very close to one another. A probe must be either doubly tuned on the high frequency channel to both 19F and 1H or the broadband channel must be able to be tuned as high as 19F. In either case, additional filters are usually required.