ReichardtPolarityParameter

The ReichardtPolarityParameter, often denoted as π*, is a quantitative measure of the polarity of a solvent. It was developed by Reichardt and coworkers to provide a consistent and experimentally accessible scale for solvent polarity that correlates with various spectroscopic and chemical phenomena. The parameter is typically determined by observing the longest wavelength absorption (λmax) of a specific solvatochromic dye, such as 3-methyl-1-(4-pyridinio)propan-1-one. The position of this absorption maximum is sensitive to the electronic environment of the solvent, and thus to its polarity.

A higher ReichardtPolarityParameter value indicates a more polar solvent. This parameter is particularly useful in organic chemistry and physical chemistry for predicting or explaining how solvent polarity influences reaction rates, equilibrium positions, and spectroscopic properties of solutes. It is often used in conjunction with other solvent parameters to build more complex models of solvent effects. The π* scale is dimensionless and is primarily a measure of the solvent's ability to stabilize a charge separation or dipole through dipolar or polar interactions. It is distinct from other polarity scales like the Kamlet-Taft parameters, which also consider hydrogen bonding capabilities.