The α₁-scale of solvent hydrogen-bond donor (hbd) acidities in dmso-water mixed solvents

The method cf solvatochromic comparisons of UV-VIS spectral data is employed to determine the α₁ values of solvent ability to donate a proton to a solute (type-A hydrogen bonding) for a series of binary DMSO-water mixed solvents. The magnitudes of enhanced solvatochromic shifts in hydrogenbond donor (HBD) solvents are determined by using 2,6-diphenyl-4-(2,4,6-triphenyl-l-pyridino)phenoxide, 2, as the solute (indicator), with the UV-VIS spectral absorption of 4-nitroanisole, 1, as the reference. It is shown that the α₁ values of solvent hydrogen-bond acidity decrease with increasing composition of the non-protic solvent DMSO in a series of DMSO-water mixed solvents. The empirical solvent polarity E_T(30) and EC parameters for the same series of DMSO-water mixtures have also been obtained in the course of the study and are reported herein.