Intramolecular Solvation of Carboxylate Anions in the Gas Phase

Proton exchange reactions between acetate, n-butanoate, 2-ethylhexanoate, and n-decanoate were studied experimentally by the use of PHPMS and theoretically by the use of ab initio methods. The occurrence of a curvature in some of the van't Hoff plots suggests isomerization of at least one of the participants in the equilibrium. This isomerization is suggested to be an intramolecular solvation of the carboxylate anions via unconventional hydrogen bonding. These interactions are discussed in terms of charge distributions in the unfolded and folded conformers of the carboxylates. Thermochemical values for the intramolecular solvation were deconvoluted from the curved van't Hoff plots by a fitting procedure. The thermochemical data for the intramolecular solvation was used to calculate the conformer composition of the carboxylate anions. Various properties related to the intramolecular solvation of the carboxylate anions are discussed.