Unusual ionic hydrogen bonds: Complexes of acetylides and fluoroform

Ion-molecule complexes of substituted acetylides, RCC- (R = tert-butyl, H, phenyl, p-tolyl), and fluoroform, HCF3, were studied using Fourier transform ion cyclotron resonance mass spectrometry. These complexes, RCC-. HCS, all have complexation energies of approximately -19 kcal/mol and are, therefore, hydrogen bonded. The acetylides vary in basicity over a 6 kcal/mol range, but all have the same complexation energy with fluoroform. The structure of these complexes was verified by deuterium isotopic exchange reactions and equilibrium fractionation experiments. The relationship between acid-base thermochemistry and hydrogen bond stability is discussed.