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 Hay and Wadt pseudopotential for the Br atom. Calculations at the MP2, MP3 and MP4 levels established two stable structural isomers for the C6H4Br− ion: (a) a bromphenide anion and (b) an isomer with a loose hydrogen-bonded bromide-benzyne complex where the Br− ion is straddling the ortho and meta hydrogen of the ring. At the MP4 level the barrier between the two isomers is below the typical energies associated with the loose complexes formed as intermediates in ion/molecule reactions.