Reactions of Alkenes

This video demonstrates three classic reactions of the alkenes. The alkene used in this video is cyclohexene.
In the first demonstration, a sample of cyclohexene is burnt. Alkenes generally burn with a smoky flame. The reason behind this is complicated and relates to the propensity of alkene molecules to combine to make special molecules that chemists call 'aromatic'. These are found in soot.
In the second demonstration, a sample of cyclohexene is shaken with bromine water. This is accompanied by a colour change from orange to colourless. This is an addition reaction. The products is called 1,2-dibromocyclohexane.
In the final demonstration, a sample of cyclohexene is shaken with acidified potassium permanganate solution. This is accompanied by a colour change from purple to colourless. This is an addition reaction. The product is called cyclohexan-1,2-diol. This is a complicated reaction that can produce many side products. The reagent can also potentially react with alkanes. It is therefore common to attenuate the power of the permanganate by using a cold, dilute and alkaline solution. The corresponding colour change in this case would be from purple to green, ultimately leading to a brown precipitate (MnO2).