It’s now time to go back to the structure of benzene. Benzene is unusually stable for an alkene and is not normally described as an alkene at all. For example, whereas normal alkenes (whether conjugated or not) readily react with bromine to give dibromoalkane addition products, benzene reacts with bromine only with difficulty—it needs a catalyst (iron will do) and then the product is a monosubstituted benzene and not an addition compound.

Bromine reacts with benzene in a substitution reaction (a bromine atom replaces a hydro gen atom), keeping the benzene structure intact. This ability to retain its conjugated structure through all sorts of chemical reactions is one of the important differences between benzene and other alkenes.