On Aug 15, 2022 Ivo Leito gave a presentation Acidities of Fluorocompounds at the 20^th European Symposium on Fluorine Chemistry taking place in Berlin (Germany) during Aug 12-19, 2022.

Fluorination, especially polyfluorination is a powerful means for acidifying molecules. So, many fluorine-containing compounds are acidic (Scheme on the left) and some are remarkably strong acids, e.g. the well-known trifluoromethanesulfonic acid CF₃SO₃H or the bis(trifluoromethane)sulfonimide (CF₃SO₂)₂NH.

The first part of the presentation gave a brief overview of the acidity of molecules, expressed as pK_a values, acidity scales (pK_a scales) on the example of the acetonitrile pK_a scale and discussed two important pK_a measurement methods: UV-Vis and NMR spectrometry.

The second part of the presentation specifically addressed the relative pK_a measurement method based on ¹⁹F NMR for accurate measurement of pK_a values of fluorocompounds (Scheme on the right). The presentation demonstrated that ¹⁹F NMR has a number of advantages, compared to most other methods: accurate concentrations of acids not needed, method is tolerant to impurities in compounds, several compounds can be measured simultaneously, solvent or titrant signals do not hinder measurements and deuterated solvents are not needed. Using multiple relative measurements against several reference compounds with known acidities, it is possible to obtain highly reliable pKa values.