GAS-PHASE H D EXCHANGE BETWEEN ARENIUM IONS AND SELECTED BASES - THE SITE OF PROTONATION OF SIMPLE AROMATICS/

H/D exchange between arenium ions bearing various substituents (Y = Et , Me2CH, CF3, CF3CO, NO2, Me3Si) on a perdeuterated ring and bases hav ing at least one H atom at the active site are described. A radiolytic technique operating at atmospheric pressure and allowing the recovery of neutral end products was used. The exchange depends on features of both the base (structure, proton affinity) and the arenium ion. The e lementary step for back proton transfer from the protonated base to th e neutral arene has been studied by NMR analysis of the H distribution within YC6D4H. The protonation was found to involve the most basic ri ng positions: ortho/para for alkyl substituents (Y = Et, Me2CH) and or tho/meta for electron-withdrawing substituents (Y = CF3, CF3CO, NO2).