The Gutmann Acceptor- (AN) and
Donor Number (DN) are measures of the
strength of solvents as Lewis acids or bases.
The Acceptor Number is based on the 31P-NMR chemical shift of
triethylphosphine oxide in the solvent.
The Donor Number is based on the heat of reaction between the compound dissolved in CH2ClCH2Cl and
SbCl5, and is therefore a 'solute' rather than a 'solvent' scale.
Because SbCl5 is decomposed by protic compounds, e.g. alcohols, the Donor Numbers for these
have to be determined by indirect methods.
The Acceptor Number is a measure of hydrogen bond acidity and correlated with other hydrogen bond acidity scales such as
→ Dimroth-Reichardt ET
(→ ET vs AN) and
→ Swain Acity
(→ Acity vs AN).
Correlation with
→ Kamlet-Taft α and
→ Catalán SA is weaker.
The Donor Number is correlated with → Kamlet-Taft β
(→ β vs DN).
See →
"The donor-acceptor approach to molecular interactions" by V. Gutmann, Plenum Press, New York and London (1978),
and →Lewis donor strength for scales of Lewis bases.
Note: AN values in parenthesis are estimated from the corresponding Dimroth-Reichardt ET-values.