Solvatochromism: A Comprehensive Project for the Final Year Undergraduate Chemistry Laboratory

A project for last year students of Chemistry based on solute-solvent interactions from the Physical Chemistry point of view is presented. The UV-Visible solvatochromic effect is used to characterize the solvent polarity. Three different solvatochromic probes, 4-Nitroanisol, 4-Nitrophenol and Reichardt’s dye Betaine (ET30) have been used to estimate the polarity parameters for eight organic solvents. Kamlet-Taft and Dimroth–Reichardt solvent scales are utilized to estimate the solvent polarity via parameters related with the dispersive forces, dipolar interactions and the tendency to H bond formation. Inside the framework of Linear Free Energy Relationships (LFER), literature data have been utilized to check the validity of these solvent models. The pKa values are analyzed to show the influence of the aprotic solvent polarity in the chemical equilibrium. The change in chemical rate constant of solvolysis due to the solvent polarity displays their possible influence in reaction mechanism. Good replications are obtained with the solvatochromic parameters by means of multi-linear regression relationship, for both LFER data.