In chemistry a donor number (DN) is a quantitative measure of Lewis basicity.
A donor number is defined as the negative enthalpy value for the 1:1 adduct formation between a Lewis base and the standard Lewis acid SbCl5 (antimony pentachloride), in dilute solution in the noncoordinating solvent 1,2-dichloroethane with a zero DN.
[1] The donor number is a measure of the ability of a solvent to solvate cations and Lewis acids.
Typical solvent values are:[3] The donor number of a solvent can be measured via calorimetry, although it is frequently measured with nuclear magnetic resonance (NMR) spectroscopy using assumptions on complexation.
[4] A critical review of the donor number concept has pointed out the serious limitations of this affinity scale.