A measure of the capability of a solute for hydrophobic lipophilic interaction based on the partition coefficient \(P\) for distribution of the solute between octan-1-ol and water. The most general way of applying \(P\) in correlation analysis, QSAR, etc. is as log \(P\), but the behaviour of substituted benzene derivatives may be quantified by a substituent constant scale, \(\pi \), which is defined in a way analogous to the Hammett $\ce{\upsigma\!}$ scale. There are various scales, depending on the substrate series used as reference.