In chemistry a donor number or 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. The units are kilocalories per mole for historical reasons. The donor number is a measure of the ability of a solvent to solvate cations and Lewis acids. The method was developed by V. Gutmann in 1976. Likewise Lewis acids are characterized by acceptor numbers.
Typical solvent values are:
- acetonitrile 14.1 kcal/mol (59.0 kJ/mol)
- acetone 17 kcal/mol (71 kJ/mol)
- methanol 19 kcal/mol (79 kJ/mol)
- tetrahydrofuran 20 kcal/mol (84 kJ/mol)
- dimethylformamide (DMF) 26.6 kcal/mol (111 kJ/mol)
- dimethyl sulfoxide (DMSO) 29.8 kcal/mol (125 kJ/mol)
- ethanol 31.5 kcal/mol (132 kJ/mol)
- pyridine 33.1 kcal/mol (138 kJ/mol)
- triethylamine 61 kcal/mol (255 kJ/mol)
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