Abstract
The interaction energies of CH/sub 3/COO/sup -/ 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 ..delta..H/sub condsn/(H/sub 2/O) shows that ionic interactions are accounted for mostly by the first two solvent molecules. CH/sub 3/COO/sup -/ hydrogen bonds strongly to NH acids such as pyrrole, amides, and aniline, with ..delta..H/sup 0//sub D/ = 25-31 kcal/mol. With the carbon acids CH/sub 3/CHO, CH/sub 3/COCH/sub 3/, and CH/sub 3/CN as ligands, the attachment energies are 14-16 kcal/mol and the interactions may involve multiple O/sup -/..HC bonds. Despite the fact that the ions CH/sub 3/COO/sup -/, Cl/sup -/, CN/sup -/, and SH/sup -/ differ in size, structure, electronegativity, isotropy, and available bonding sites, they bond with similar strengths to most OH, NH, and CH hydrogen donors, from H/sub 2/O to large organic molecules such as the dipeptide analogue CH/sub 3/CO-Ala-OCH/sub 3/. Also, the four ions show similar clustering energies with n H/sub 2/O and HCN molecules (n = 1-4).
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