Partition Coefficient
The equilibrium ratio of a solute's concentrations in two immiscible phases.
Formula / equation
P = C₁ / C₂
Unit
Dimensionless
In depth
Usually quoted as log P for the octanol–water system, the coefficient measures how lipophilic a compound is. It is a key predictor of whether a drug will cross cell membranes, how a pollutant will accumulate in fatty tissue, and how a compound will behave in chromatography.
Examples in the real world
Aspirin has log P ≈ 1.2; highly lipophilic pesticides with log P above 5 bioaccumulate in food chains.