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    Would cycloalkanes quickly decolourise bromine water? Surely, if they don't have a double bond they wouldn't..

    PS. ( I ask this because, in an SQA exam, one of the MCQ answers was that cyclopropane quickly decolourises bromine water)

    Surely it doesn't? Does it?
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    (Original post by Jar_Man)
    Would cycloalkanes quickly decolourise bromine water? Surely, if they don't have a double bond they wouldn't..

    PS. ( I ask this because, in an SQA exam, one of the MCQ answers was that cyclopropane quickly decolourises bromine water)

    Surely it doesn't? Does it?
    You are right about cycloalkanes, but cyclopropane is the exception to the rule. Because the bonds are so strained to keep it's cyclic nature with only three bonds (60 degree C-C bonds required when optimum is 109.5), it is actually very reactive and is succeptible to electrophilic attack by bromine to form 1,3-dibromopropane.
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    Ring strain in smaller carbon rings ie cyclepropane will include angle strain and eclipsing strain. Angle strain is expecially severe in this molecule as it's so small. Cyclopropane will undergo electrophilic addition reactions and BrCH2CH2CH2Br will result when Br2 is added.

    So to answer your question, only lower members of this series such as cyclopropane and cyclobutane will decolourise Br2 due to bond strain.
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    Thanks alot! I'd rep you both, but my rep isnt worth much!
 
 
 
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