SITE OF PROTONATION AND CONFORMATIONAL EFFECTS ON GAS-PHASE BASICITY IN beta -AMINO ALCOHOLS. THE NATURE OF INTERNAL H BONDING IN beta -HYDROXY AMMONIUM IONS.

Article abstract of DOI:10.1021/ja00349a006

The influence of interfunctional distance on the gas-phase basicity of beta -amino alcohols is investigated by the method of equilibrium proton-transfer reactions in an ion cyclotron resonance (ICR) spectrometer. It is found that in the protonated species, interaction between the most basic center (amino group) with the hydroxy group results in stabilization of the system. The stabilization energy increases as the interfunctional distance decreases to reach a maximum value of about 7 kcal/mol for coplanar systems. Comparison with the values determined by ab initio calculations indicates that internal H bonding can be described in terms of the ion-dipole potential energy between the ammonium ion and the hydroxy group. External vs. internal ion solvation effects are also discussed.