Ionic Hydrogen Bond and Ion Solvation. 6. Interaction Energies of the Acetate Ion with Organic Molecules. Comparison of CH3COO- with Cl-, CN-, and SH-

Article abstract of DOI:10.1021/ja00220a021

The interaction energies of CH3COO^- with protic and aprotic molecules were measured by pulsed high-pressure mass spectrometry.The attachment energies of the first three water molecules are 15.8, 12.8, and 11.8 kcal/mol.The rapid approach to ΔH_condsn(H2O) shows that ionic interactions are accounted for mostly by the first two solvent molecules.CH3COO^- hydrogen bonds strongly to NH acids such as pyrrole, amides, and aniline, with ΔH^o_D = 25 - 31 kcal/mol.With the carbon acids CH3CHO, CH3COCH3, and CH3CN as ligands, the attachment energies are are 14-16 kcl/mol and the interactions may involve multiple O^-..HC bonds.Despite the fact that the ions CH3COO^-, Cl^-, CN^-, and SH^- differ in size, structure,electronegativity, isotropy, and available bond sites, they bond with similar strengths to most OH, NH, and CH hydrogen donors, from H2O to large organic molecules such as the dipeptide analogue CH3CO-Ala-OCH3.Also, the four ions show similar clustering energies with n H2O and HCN molecules (n = 1-4).