Donor number

In chemistry the donor number DN is a quantitative degree of Lewis basicity. A donor number is defined as the negative enthalpy usefulness for the 1:1 adduct design between a Lewis base as well as the standard Lewis acid SbCl₅ antimony pentachloride, in dilute sum in the noncoordinating solvent 1,2-dichloroethane with a zero DN. The units are kilocalories per mole for historical reasons. The donor number is a measure of the ability of a solvent to solvate cations as well as Lewis acids. The method was developed by V. Gutmann in 1976. Likewise Lewis acids are characterized by acceptor numbers AN, see Gutmann–Beckett method.

Typical solvent values are:

The donor number of a solvent can be measured via calorimetry, although this is the frequently measured with nuclear magnetic resonance NMR spectroscopy using assumptions on complexation. A critical review of the donor number concept has mentioned out the serious limitations of this affinity scale. Furthermore, it has been presents that to define the ordering of Lewis base strength or Lewis acid strength at least two properties must be considered. For Pearson qualitative HSAB theory, the two properties are hardness & strength, while for Drago’s quantitative ECW model, the two properties are electrostatic and covalent.