Donor number

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.^[1] 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.^[2] Likewise Lewis acids are characterized by acceptor numbers (AN, see Gutmann-Beckett method).

Typical solvent values are:^[3]

• 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)

References

1. Françoise Arnaud-neu, Rita Delgado, and Sílvia Chaves (2003). "Critical evaluation of stability constants and thermodynamic functions of metal complexes of crown ethers". Pure Appl. Chem. 75 (1): 71–102. doi:10.1351/pac200375010071.
2. V. Gutmann (1976). "Solvent effects on the reactivities of organometallic compounds". Coord. Chem. Rev. 18 (2): 225. doi:10.1016/S0010-8545(00)82045-7.
3. D.T. Sawyer, J.L. Roberts (1974). Experimental Electrochemistry for Chemists. John Wiley & Sons, Inc.

Further reading

• IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "donor number".