RING-OPENING REACTION OF PROTONATED POLYFLUORINATED BENZENES IN THE GAS-PHASE - A THEORETICAL MNDO STUDY

The MNDO calculations of protonated polyfluorobenzenes [Ph‐Fn]H+ indicate the possibility of a relatively free migration of the hydrogen proton with energy barriers of 125–145 kJ mol−1. At a higher degree of substitution (n) the protonation of the ipso carbon atom occupied by fluorine becomes energetically feasible, along with analogous migrations of fluorine, which, however, are energetically the most advantageous (ΔEa ∼ 230 kJ mol−1). In addition to bridged fluoronium ions, relatively stable cyclic intermediates were also found, which make possible a rearrangement to the difluoromethylenecyclopentadienyl cation and thus the elimination of CF2 observed in collision‐induced dissociation mass spectra. Copyright © 1990 John Wiley & Sons, Ltd.