New 19 F NMR methodology reveals structures of molecules in complex mixtures of fluorinated compounds

Although the number of natural fluorinated compounds is very small, fluorinated pharmaceuticals and agrochemicals are numerous. F NMR spectroscopy has a great potential for the structure elucidation of fluorinated organic molecules, starting with their production by chemical or chemoenzymatic reactions, through monitoring their structural integrity, to their biotic and abiotic transformation and ultimate degradation in the environment. Additionally, choosing to incorporate F into any organic molecule opens a convenient route to study reaction mechanisms and kinetics. Addressing limitations of the existing F NMR techniques, we have developed methodology that uses F as a powerful spectroscopic spy to study mixtures of fluorinated molecules. The proposed F-centred NMR analysis utilises the substantial resolution and sensitivity of F to obtain a large number of NMR parameters, which enable structure determination of fluorinated compounds without the need for their separation or the use of standards. Here we illustrate the F-centred structure determination process and demonstrate its power by successfully elucidating the structures of chloramination disinfectant by-products of a single mono-fluorinated phenolic compound, which would have been impossible otherwise. This novel NMR approach for the structure elucidation of molecules in complex mixtures represents a major contribution towards the analysis of chemical and biological processes involving fluorinated compounds.