Dissociation Constant
The equilibrium constant for the breaking apart of a compound or complex into smaller species.
Formula / equation
Kd = [A][B] / [AB]
Unit
mol/L
In depth
A large dissociation constant indicates a weakly held association, while a small one indicates a tight one. The concept spans weak acids, complex ions and biological binding, where Kd for a drug–receptor pair is the concentration at which half the receptors are occupied.
Examples in the real world
Oxygen binds haemoglobin with a Kd of about 26 torr; ethanoic acid has Ka = 1.8 × 10⁻⁵.