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

Kacper Błaziak; Przemysław Sendys; Witold Danikiewicz

doi:10.1002/cphc.201501101

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

Chemphyschem. 2016 Mar 16;17(6):850-8. doi: 10.1002/cphc.201501101. Epub 2016 Jan 26.

Authors

Kacper Błaziak¹, Przemysław Sendys¹, Witold Danikiewicz²

Affiliations

¹ Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224, Warsaw, Poland.
² Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224, Warsaw, Poland. witold.danikiewicz@icho.edu.pl.

PMID: 26728759
DOI: 10.1002/cphc.201501101

Abstract

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 RMSEPBE0 =1.7, RMSEB3LYP =4.6, RMSEM05-2X =6.6, RMSEG3MP2 =6.3, RMSEG4MP2 =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: RMSEPBE0 =1.9, RMSEB3LYP =4.5, RMSEM05-2X =6.3, RMSEG3MP2 =4.9, RMSEG4MP2 =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.

Keywords: carboxylate anions; density functional calculations; phenide ions; proton affinity; quantum chemistry.