A solvent parameter defined by:
derived from the Gibbs energy of transfer () of a series of solutes from water to numerous aqueous-organic mixtures and to pure solvents:
where is a solute parameter, and and characterize the solvent. The values are used to define a solvent solvophobic effect so that values are scaled from unity (water) to zero (hexadecane).
PAC, 1994, 66, 1077 (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1165