Hydrogen-bonded complexes of methanol and acetylides. Structure and energy correlations

We examine the connection between acid-base chemistry and hydrogen bond stability for anionic ion-molecule complexes. Ion-molecule complexes of substituted acetylides, RCC- (R = tert-butyl, H, phenyl, p-tolyl), and methanol were studied using Fourier transform ion cyclotron resonance mass spectrometry. These complexes, RCC-. HOCH3, all have complexation energies of -21 kcal/mol and are, therefore, hydrogen bonded. The acetylides vary in basicity over an 8 kcal/mol range, but all have the same complexation energy with methanol. In contrast, results reported by Bartmess show that the complexation energies of aliphatic alcohols with phenyl acetylide vary with the acidity of the alcohol. These results show that the frequently observed relationship between acid-base energetics and complexation energy is a property of the specific system and not a general one. We believe that these results demonstrate that the existence, and magnitude, of these correlations cannot be used to infer structural information about the complexes.