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A recent method for determination of stoichiometries and binding constants for short-range, hydrogen bonding solvation is reviewed and new results are presented. The method exploits the sensitivity of a proton-transfer equilibrium, K PT to changes in solvent composition. Solvation numbers and binding constants for primary and secondary stages of solvation of an aminephenol proton-transfer adduct and the phenol and amine are determined as adjustable parameters when model isotherms are fitted to K PT versus [ S ] data, where [ S ] is the concentration of a hydrogen-bonding minor component of a mixed solvent, Results for most of the twenty-three aprotic solvents investigated are modeled by bifurcation-type hydrogen bonding of two or more electron pairs to a single polar hydrogen. Results for the seven protic solvents studied, including new data for ethanol, 2-choloroethanol, and 2,2-dichloroethanol, are modeled by two, or possibly three, successive stages of solvation, assumed to involve hydrogen-bonded chains. Preliminary results indicate that solvation by water is amenable to this analysis. |
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