Kamlet–Taft solvent parameters

https://doi.org/10.1351/goldbook.K03367
Parameters of the Kamlet–Taft solvatochromic relationship which measure separately the hydrogen bond donor ($\ce{\upalpha\!}$), hydrogen bond acceptor ($\ce{\upbeta\!}$), and dipolarity/polarizability ($\ce{\uppi\!^{\ast}}$) properties of solvents as contributing to overall solvent polarity.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1132 [Terms] [Paper]