Proton transfer between functional groups in MH + ions of stereoisomeric diethers on chemical ionization and collision-induced dissociation conditions

Abstract

Proton transfer between functional groups in the MH + ions of stereoisomeric mixed methyl ethyl diethers of trans-tricyclo[6.2.2.0 2,7]dodeca-9-en-3,6-diols 1t and 2t, obtained on isobutane chemical ionization (CI), was investigated by a comparison of their CI and collision-induced dissociation (CID) mass spectra. Preferential elimination of the alcohol originating at the exo-alkoxyl was observed under CI conditions, whereas loss of the protonated endo-alkoxyl was predominant in the CID measurements of the MH + ions. These results indicate preferential initial CI protonation at the exo-alkoxyl group, followed by elimination of the alcohol originating at that position, and predominant retention of the proton at the endo-alkoxyl in the surviving MH + ions which are submitted to the collision cell. These findings lead to the conclusion that the external proton does not migrate from its original protonation site to the endo-alkoxyl to an appreciable extent, if at all, during the course of CI and CID experiments. This method of exploring the question of occurrence of interfunctional proton transfer processes in gas-phase protonated difunctional compounds may be applied in other systems.