1,8-Dimethylnaphthalene, perinaphthane and pleiadene were synthesized to form, with acenaphthene, a group of structurally analogous hydrocarbons. Acenaphthene was brominated under a variety of conditions and the distributions of the product isomers were measured by vapor phase chromatography. A selection of the brominating conditions was then tried on the group of hydrocarbons in an endeavour to relate the isomer distributions to the structural differences between the hydrocarbons. Finally, pairs of the hydrocarbons were brominated to determine their order of reactivity. The inferences that may be drawn from the results are discussed together with their reproducibility and reliability.