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    How do I know an unknown organic compound is an alkene or phenol by using chemical tests(no NMR OR INFR)
    thanks!!
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    When bromine water is added to an alkene, it decolourises.
    Same with phenol.
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    Phenol forms a complex with Fe3+. So if you add phenol to some Iron (III) chloride, you will see a deep purple solution form ... this can be used as a test for phenol.

    Also phenol is acidic whereas alkenes are not. So you could simply add some indicator to each, or add a carbonate and test for CO2 given off in the acid base reaction (from phenol).
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    sorry, my bad English!! I mean how to distinguish which is alkene, which is phenol. Is that when I add bromine water, both will let bromine
    water decolourised,but in phenol will form white precipitate??
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    phenol is slightly acidic... alkenes are neutral...
    phenol is slightly soluble in water... alkenes are not...
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    (Original post by John714)
    How do I know an unknown organic compound is an alkene or phenol by using chemical tests(no NMR OR INFR)
    thanks!!
    alkene decolourises bromine water and potassim manganate. phenol doesnt do either (no change) as the bonds are not totally unsaturated
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    (Original post by endeavour)
    When bromine water is added to an alkene, it decolourises.
    Same with phenol.

    phenol cannot decolourise bromine water but an alkene can. phenol's bonds are as decibed in the kekule structure, neither single or double. only a double bond as in an alkene can partake in the electrophilic addition as in the alkene reaction. phenol cannot break any of the arene bonds except under extreme heat/pressure as in the nuclophilic addition of Na+.hence u r wrong.
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    but in my chemistry2 book says Aqueous phenol decolourises bromine water to form a white precipitate of 2,4,6-tribromophenol.
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    (Original post by magiccarpet)
    phenol cannot decolourise bromine water but an alkene can. phenol's bonds are as decibed in the kekule structure, neither single or double. only a double bond as in an alkene can partake in the electrophilic addition as in the alkene reaction. phenol cannot break any of the arene bonds except under extreme heat/pressure as in the nuclophilic addition of Na+.hence u r wrong.
    But we're talking about phenol, not just benzene.

    Phenol's hydroxy group activates the benzene ring, as electrons from the oxygen are donated into the delocalised pi system at carbon 2,4 and 6 (hence why you get 2,4,6-tribromophenol).
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    i will **** myself if u r right.

    the only other thing i can think of is if u react it with sodium carbonate in neutralisation reaction. alkene will not react, phonol will. wil get fizzing and hissing
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    (Original post by endeavour)
    But we're talking about phenol, not just benzene.

    Phenol's hydroxy group activates the benzene ring, as electrons from the oxygen are donated into the delocalised pi system at carbon 2,4 and 6 (hence why you get 2,4,6-tribromophenol).
    agree
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    Yes - phenol will react with bromine in a very vigorous electrophilic substitution reaction in the 2,4,6 positions of the benzene ring. The OH group is extremely activating as one of the lone pairs on the oxygen can be donated to the ring pi system.
 
 
 

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