Acidity functions from carbon-13 NMR

Perfluoroalkyl Phosphonic and Phosphinic Acids as Proton Conductors for Anhydrous Proton‐Exchange Membranes

“…The two perfluorinated phosphonic and phosphinic acid model compounds have intermediate acid strengths on this scale and they are slightly more acidic than phosphoric acid, which has a Hammett acidity of À6.25. [25] This finding is consistent with the expected action of perfluoroalkyl substituents, which are electron-withdrawing and should stabilize conjugate bases, thereby increasing the acid strength. Thus, it appears that no direct correlation can be drawn between the acidity of the model compounds and their anhydrous ionic conductivity.…”

“…Mesityl oxide was used as the indicator in this study, as described by Farcasiu and Ghenciu. [25,26] The method describes that the 13 C NMR chemical shift difference (Dd) between the C a and C b carbon atoms of mesityl oxide increases with increasing degree of protonation and a graph of (Dd) versus concentration of mesityl oxide has a linear form. From this graph, the y-axis intercept of the chemical shift difference (Dd 0 ) was taken as the value that corresponds to the H 0 value of the acid.…”

Investigating the Weak to Evaluate the Strong: An Experimental Determination of the Electron Binding Energy of Carborane Anions and the Gas phase Acidity of Carborane Acids

“…Comparisons are made to the bis(nonafluorobutane-1-sulfonyl)imide ion, (1-C 4 F 9 SO 2 ) 2 N -, whose conjugate acid is currently the strongest gas phase acid to be determined experimentally. 9 Five CHB 11 X 6 Y 5 -carborane anions from the series X ) Br, Cl, I and Y ) H, Cl, CH 3 were readily generated in a Fourier transform mass spectrometer (FTMS) by electrospray ionization of aqueous methanolic solutions of the corresponding cesium salts. 10 Each anion was allowed to react with a series of Brønsted acids of known strength including CF 3 SO 3 H (∆H°a cid ) 305.4 ( 2.2 kcal mol -1 ) 11 and (1-C 4 F 9 SO 2 ) 2 NH (∆H°a cid ) 291.1 ( 2.2 kcal mol -1 ), 9 but no reactions were observed indicating that the proton affinities of all five anions are less than 291.1 ( 2.2 kcal mol -1 .…”

The Strongest Isolable Acid

“…The chosen method is adapted from that developed by Fǎ rcaşiu and Ghenciu. [7] It is based on the 13 C NMR spectroscopy chemical shift difference (Dd) between the C a and C b carbon atoms of mesityl oxide which increases with increasing protonation as Equation (2) is shifted to the right hand side. 13 C NMR spectroscopy data for 0.15 m solutions of various acids and 0.10 m mesityl oxide were obtained at room temperature and are given in Table 1.…”