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Bromination of Pentene

Bromine is added to pentane and pentene. In the absence of intense light, only pentene reacts.

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Narrative
Bromine dissolved in carbon tetrachloride is added to pentane and pentene. The pentane does not react with the bromine and the solution stays orange. When bromine is added to pentene, the solution eventually becomes clear. In pentene, bromine adds across the double bond to produce 1,2 -dibromopentane, which is colorless.