Role of hydroxyl concentrations in solvatochromic measures of solvent polarity of alcohols and alcohol-water mixtures-evidence that preferential solvation effects may be overestimated.
For single solvents, primary alcohols and water, there is a good linear correlation (r = 0.994) between the solvent polarity index ET(30) and the molar concentration of OH groups (or 1000/Vm, where Vm is the solvent molar volume). The corresponding correlations for alcohol-water mixtures are plots vs. the sum of molar concentrations of alcohol and water, alternatively expressed as plots of ET(30)vs. volume fraction. Our quantitative treatment is an extension of recent theoretical and experimental results. In contrast, previous studies of alcohol-water mixtures have relied on plots of ET(30)vs. mole fraction, and have overestimated the effect of preferential solvation of solvatochromic dyes by the more hydrophobic alcohols.
Department of Chemistry, University of Wales, Swansea, Singleton Park, Swansea, Wales, UK SA2 8PP. cmsolvol@swansea.ac.uk
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