Abstract Labelling studies show that dehydrohalogenation of the tetrahalobicycloheptane (8b, c) yields the title compounds (5a, b) both with and without skeletal rearrangement. 2- Chlorocyclopropabenzene (5b) is the major product and the expected 2-bromo derivative (5a) the minor product of reaction from the 'mixed'tetrahalide (8c).