Acidity, basicity, and the stability of hydrogen bonds:: Complexes of RO-+HCF3

Ion-molecule complexes of RO- (R = Me, Et, i-Pr) and HCF3 have been studied with Fourier transform ion cyclotron resonance spectrometry. The RO- complexation energies with HCF3 were measured relative to RO-. H2O. These complexes, [ROHCF3](-), have complexation energies on the order of -20 kcal/mol and have low deuterium fractionation factors and are, therefore, hydrogen bonded. The structure of the complexes was studied by isotopic equilibrium experiments and ab initio calculations. All of the complexes studied have the structure RO-. HCF3 even when HCF3 is a stronger acid than ROH. The structure of the complexes can be understood through electrostatic arguments rather than the difference in acidity between the ion and neutral.