Experimental versus Calculated Proton Affinities for Aromatic Carboxylic Acid Anions and Related Phenide Ions

Herein, we present the comparison of a large set of experimentally measured proton affinity (PA) values for 65 aromatic carboxylate anions with the values calculated by using selected popular DFT (B3LYP, PBE0, and M05‐2X) and composite G3(MP2), G4(MP2)] quantum chemistry methods. The root‐mean‐square error (RMSE) values for the chosen methods are RMSE_PBE0=1.7, RMSE_B3LYP=4.6, RMSE_M05‐2X=6.6, RMSE_G3MP2=6.3, RMSE_G4MP2=4.5 kJ mol^?1. In the second part of the study, 82 PA values for substituted phenide ions and a few heteroaromatic anions were calculated. Again, very good agreement between the calculated and experimental values has been observed: RMSE_PBE0=1.9, RMSE_B3LYP=4.5, RMSE_M05‐2X=6.3, RMSE_G3MP2=4.9, RMSE_G4MP2=5.5 kJ mol^?1. Our results show that, for medium‐sized carboxylate anions, all tested methods give reliable results and, surprisingly, much more computationally demanding composite methods do not perform significantly better than the time‐efficient DFT methods.