Effect of the medium on the reaction of 4-methyl-7-azaindoline with acetic and trifluoroacetic acids

The effect of the medium on the equilibrium involved in proton transfer via a hydrogen bond and dissociation of ion pairs in systems composed of 4-methyl-7-azaindoline and acetic and trifluoroacetic acids was examined by means of PMR and IR spectroscopy. The position of the molecular H complex ? ion pair equilibrium depends on the proton-donor-acceptor properties of the solvent and is shifted to favor the ionic form in the order CH₃CN < CH₂Cl₂< CDCl₃. A change in the dielectric constant of the medium affects mainly the degree of dissociation of the ion pairs.