Koppel–Palm solvent parameters

Parameters to measure separately the ability of a solvent to enter into non-specific solvent–solute interactions (permittivityɛ and refractive indexη D) and specific solvent–solute interaction (solvent basicity or nucleophilicityB and solvent acidity or electrophilicityE) as contributing to overall solvent polarity.
Source:
PAC, 1994, 66, 1077 (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1134