A THEORETICAL-STUDY OF ISOMERIC C6H4BR- IONS

The structural stability of bromide o-benzyne complexes was studied. A new procedure was applied to adapt a basis set to be used with the Ha y and Wadt pseudopotential for the Br atom. Calculations at the MP2, M P3 and MP4 levels established two stable structural isomers for the C6 H4Br- ion: (a) a bromphenide anion and (b) an isomer with a loose hydr ogen-bonded bromide-benzyne complex where the Br- ion is straddling th e ortho and meta hydrogen of the ring. At the MP4 level the barrier be tween the two isomers is below the typical energies associated with th e loose complexes formed as intermediates in ion/molecule reactions.