Hydrogen-Bond Acceptance of Solvents: A 19F Solvatomagnetic β1 Database to Replace Solvatochromic and Solvatovibrational Scales

A variety of physicochemical properties and several hydrogenbond donors have been used to define methods and to build scales aiming at measuring the hydrogen-bond acceptance of solvents. There is a great deal of confusion in these scales and methods. Solvatochromic, solvatocalorimetric, solvatovibrational, and F-19 solvatomagnetic comparison methods are critically reviewed. Only two methods, the solvatomagnetic and the solvatocalorimetric ones, are able to yield reliable solvent hydrogen-bond acceptance scales. The solvatomagnetic beta(1) scale defined from the F-19 chemical shift of 4-fluorophenol is extended to many solvents including ionic liquids and green solvents. The results for about 240 hydrogen-bond acceptor solvents are organized in a numerical beta(1) database. The comparison of beta(1) with solvatochromic scales highlights their shortcomings, in particular for the important class of amphiprotic solvents. Therefore, the use of the F-19 solvatomagnetic comparison method and of the solvatomagnetic beta(1) scale is recommended in solvent effect studies.