The presence of unsaturation in organic compounds can be shown by using bromine solution. It has an orange/red colour as a result of the bromine molecules it contains. When bromine solution is shaken with an unsaturated hydrocarbon the bromine molecules ‘add on’ across the carbon=carbon double bonds and the reaction mixture rapidly turns colourless. When a saturated hydrocarbon and bromine solution are mixed the orange/red colour remains.
Testing for Unsaturation – pupil
