Yukawa–Tsuno equation

A multiparameter extension of the Hammett equation to quantify the role of enhanced resonance effect on the reactivity of meta- and para-substituted benzene derivatives, e.g. \[\log _{10}k = \log _{10}k_{0}+\rho \ [\sigma +r\ (\sigma^{+}-\sigma)]\] The parameter r gives the enhanced resonance effect on the scale (σ + – σ) or (σ – σ), respectively.
See also: ρ-value, σ-constant
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1176 (https://doi.org/10.1351/pac199466051077)