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
solvatecations 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).
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.[5] 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.[6] For Pearson qualitative
HSAB theory, the two properties are hardness and strength,[7] while for Drago's quantitative
ECW model, the two properties are electrostatic and covalent.[8]
^D.T. Sawyer, J.L. Roberts (1974). Experimental Electrochemistry for Chemists. John Wiley & Sons, Inc.
^KATAYAMA, Misaki; SHINODA, Mitsushi; OZUTSUMI, Kazuhiko; FUNAHASHI, Shigenobu; INADA, Yasuhiro (2012). "Reevaluation of Donor Number Using Titration Calorimetry". Analytical Sciences. 28 (2): 103–106.
doi:
10.2116/analsci.28.103.
ISSN0910-6340.
PMID22322801.
^Laurence, C. and Gal, J-F. Lewis Basicity and Affinity Scales, Data and Measurement, (Wiley 2010) p 51 ISBN 978-0-470-74957-9
^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.
doi:
10.1021/ed054p612