Solvatomagnetic Comparison Method: A Proper Quantification of Solvent Hydrogen-Bond Basicity

Abstract

The hydrogen-bond-acceptor basicity of an important class of solvents, the amphiprotic solvents (water, alcohols, primary and secondary amides, and carboxylic acids), has not yet been properly parametrized. In this work, the first scale of solvent hydrogen-bond basicity applicable to amphiprotic solvents is established by means of a new method that compares the F NMR chemical shifts of 4-fluorophenol and 4-fluoroanisole in hydrogen-bond-acceptor solvents. This so-called solvatomagnetic comparison method is free of the shortcomings of the solvatochromic comparison method used so far and is easier to carry out than the pure base calorimetric method. The validity of the new scale is assessed by good linear correlations with spectroscopic, thermodynamic, and kinetic solute properties depending on the solvent hydrogen-bond basicity. In such correlation analysis of solvent effects on physicochemical properties, solvent and solute hydrogen-bond basicity scales must not be mixed, since it is shown here that solute and solvent scales are not equivalent. A comprehensive collection of parameters quantifying the hydrogen-bond basicity is presented for 168 solvents.

Fluorescence quenching of the N-methylquinolinium cation by pairs of water or alcohol molecules

“…We chose this alcohol due to its extremely low hydrogen-bond basicity, originated by the strong electronwithdrawing effect of the fluorine atoms. 38,39 We found that no fluorescence quenching at all was observed in the alcohol concentration range 0 to 0.39 mol dm −3 (Fig. 10S, ESI †).…”

“…59 These characteristics impede the PCET process for 2,2,2trifluoroethanol. Acetonitrile has also a very low hydrogenbond basicity and proton basicity in liquid solutions, 38,39 and is unable to participate in a PCET reaction due to lack of ionisable protons. These facts explain why acetonitrile and 2,2,2trifluoroethanol do not quench the fluorescence of the Nmethylquinolinium cation, in spite of being more easily oxidized than water.…”

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

“…In 1987, Nicolet et al published 14 an "infrared comparison method" (hereafter called Solvatovibrational Comparison Method). Lastly, in 2014, Laurence et al conceived a "Solvatomagnetic Comparison Method" 15 . These methods and the corresponding solvent scales are summarized in Table 1, as well as: for comparison some solute HB basicity scales [3][4][5][6] , the Δ(OD) 10 , Δ (OH) 11 and Δ (CO) 14 infrared scales, the β statistical scale of Kamlet et al 12,16 , and the solvatochromic scales β 1 '(NH 2 ) 17 , β 1 (NH 2 ) 18,19 , β 1 (OH) 18,19 , and SB 20 .…”

“…The solvatomagnetic comparison method compares the 19 F chemical shifts of 4fluorophenol (HBD) and 4-fluoroanisole (similar to 4-fluorophenol but non-HBD) in HBA solvents and yields the so-called solvatomagnetic β 1 parameter 15 . In the second part of this work, 19 F measurements and the deduced β 1 scale will be extended to 46 new solvents.…”

From QCA (Quantum Cellular Automata) to Organocatalytic Reactions with Stabilized Carbenium Ions

“…Quite interesting applications of trifluoroethanol, as the reaction media for challenging transformations, were recently reported 38. The remarkable possibility offered by this solvent is determined by its low nucleophilicity39 and by the exhibited unique polarity, H‐bonding donation, and solvolytic and catalytic properties played by trifluoroethanol aggregates (dimers and trimers) 40. As the compound is less nucleophilic than water (5 orders of magnitude, according to the Mayr scale), the competition for reactions in which nucleophiles are involved is less pronounced.…”