Benzene is an unsaturated hydrocarbon. an interesting property of benzene is that

It does not undergo the same types of reactions that take place with other unsaturated hydrocarbons. These other substances tend to react very readily with bromine as a test for unsaturation, leaving the reddish-brown substance as a result: benzene, however, is one of the few unsaturated hydrocarbons that does not react with bromine.