Donor number

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. 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]

A critical review of the Donor Number concept has pointed out the serious limitations of this affinity scale. [4]. Furthermore, it has been shown that to define the order of Lewis base strength (or Lewis acid strength) at least two properties must be considered. [5] For Pearson qualitative HSAB theory the two properties are hardness and strength [6] while for Drago’s quantitative ECW model the two properties are electrostatic and covalent [7].

References

  1. ↑ Françoise Arnaud-neu; Rita Delgado; 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.
  4. ↑ Laurence, C. and Gal, J-F. Lewis Basicity and Affinity Scales, Data and Measurement, (Wiley 2010) p 51 IBSN 978-0-470-74957-9
  5. ↑ Cramer, R. E., and Bopp, T. T. (1977) Great E and C plot. Graphical display of the enthalpies of adduct formation for Lewis acids and bases. Journal of Chemical Education 54 612–613
  6. ↑ Pearson, Ralph G. (1968). "Hard and soft acids and bases, HSAB, part 1: Fundamental principles". J. Chem. Educ. 1968 (45): 581–586. Bibcode:1968JChEd..45..581P. doi:10.1021/ed045p581. (Subscription required (help)).
  7. ↑ Vogel G. C.;Drago, R. S. (1996). "The ECW Model". Journal of Chemical Education. 73: 701–707. Bibcode:1996JChEd..73..701V. doi:10.1021/ed073p701.

Further reading

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