Carboxylic Acids and Their Anions. Acid and Ligand Properties

Calculated deprotonation energies of acids RCOOH (R = H, Me, CMe₃, CH₂Cl, CHCl₂, CCl₃, CH₂F, CHF₂, and CF₃) correlate satisfactorily with experimental pK _a values. The enhancing acid strength over this series is associated with the enhancing stabilization of the anionic forms, under the action of solvent inclusive. Carboxylate anions are characterized by a high proton affinity, excess electron density on the oxygen atoms, and low ionization energies of the highest occupied molecular orbitals. The anions of halogenated acids are slightly weaker donors than the anions of nonhalogenated acids. However, the fluorine derivatives have very low unoccupied ^* molecular orbitals favorable for -dative interaction with metal ions, which can provide additional stabilization of fluorocarboxylate coordination compounds.