Hansch equation

https://doi.org/10.1351/goldbook.11452

A QSAR equation that describes the relationship between the logarithm of the relative biological potency of a molecule (\(\log (1/C_{i})\)) and its electronic and hydrophobic properties: \[\log (1/C_{i}) = \rho \sigma _{i} + b\,\log P_{i} - c\,(\log P_{i})^{2}\] in which fitting to the square term provides a parabola with an associated optimum log P.

Source:
PAC, 2016, 88, 239. (Glossary of terms used in computational drug design, part II (IUPAC Recommendations 2015)) on page 247 [Terms] [Paper]