Swain–Lupton equation

A dual parameter approach to the correlation analysis of substituent effects, which involves a field constant ( $F$ ) and a resonance constant ( $R$ ). The original treatment was modified later. The procedure has been considerably applied, but also much criticized.

Source:

PAC, 1994, 66, 1077 (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1170