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Chlorination of Alkenes (Module 3)

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    I just dont get any of it/??!! can sum1 please xplain....safe
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    erm, is chlorination the addition of chorine to the double bond, saturating the alkene, making it an alkane???

    Because if it is then its an electrophillic addition reaction- meaning the negative chorine molecule (Cl2) will attack the double bond- one chorine atom adding firstly, creating a postively charged carbo-cation (or something), then the left over chloride ion attacks the positive centre of the carbo-cation, then the reaction produces a 1, 2- chloroalkane.

    i hope thats what you meant, because we havent really used the word "Chlorination" in class
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    just a slight corection, the chlorine that attacks is neutral not negative...

    What actually happens is that the pi electrons from the double bond attack the chlorine molecule, which has an induced dipole caused by approaching the electron rich double bond.

    This induced dipole makes the nearest chlorine atom of the molecule pair partially positive. On attack by the pi electron pair the chlorine - chlorine bond breaks leaving behind a negative chloride ion which then attacks the carbocation formed in the first stage.

    Overall there is addition of chlorine to the double bond, one on each carbon.

    CH2=CH2 + Cl2 --> CH2Cl-CCH2Cl

    From the point of view of the reagent (the chlorine) it has sought a negative charge (the pi elctrons) and so the mechanism is called electrophilic, the overall effect is one of addition therefore the mechanism receives the name electrophilic addition
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    (Original post by charco)
    just a slight corection, the chlorine that attacks is neutral not negative...

    What actually happens is that the pi electrons from the double bond attack the chlorine molecule, which has an induced dipole caused by approaching the electron rich double bond.

    This induced dipole makes the nearest chlorine atom of the molecule pair partially positive. On attack by the pi electron pair the chlorine - chlorine bond breaks leaving behind a negative chloride ion which then attacks the carbocation formed in the first stage.

    Overall there is addition of chlorine to the double bond, one on each carbon.

    CH2=CH2 + Cl2 --> CH2Cl-CCH2Cl

    From the point of view of the reagent (the chlorine) it has sought a negative charge (the pi elctrons) and so the mechanism is called electrophilic, the overall effect is one of addition therefore the mechanism receives the name electrophilic addition

    Thanks dude- i was a bit muddled and unsure also. So you've helped me also
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    Do you mean chlorination of alkAnes, that is what i have been studying for module 3, it is a "free-radical substitution" reaction. Explore cl-cl to u.v light, and this gives the enrgy to break the bond and it splits them into two cl atoms with a free radical. (normally use a large dot but i will use * here)
    Cl2-> Cl*+Cl*

    these Cl radicals rip an electron off an alkane (eg methane)
    forming HCL

    CH4 + Cl* -> CH3* + HCl

    then the methly radical reacts with another cl2 molecule
    CH3* +Cl2 -> CH3Cl +Cl*

    finally
    Cl* + cl* -> cl2

    or CH3* + cl* -> ch3cl

    CH3* + CH3* -> C2H6

    If there is more chlorine substitution can accour until you get

    C-CL4

    If there is excess methane the chances of this are reduced.

    THis is what we were taught chlorination refers to, but it is AlkAne not AlkEne.
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    Hmm yeah thanks people.... so we just have to learn and interpret it dont we?
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    It's just a simple SN1 reaction.
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    (Original post by Lozza)
    It's just a simple SN1 reaction.
    If you're talking about chlorination of alkEnes then I'm afraid that it most certainly is NOT

    a. it's not substitution it's addition
    b. it's not nucleophilic its electrophilic
    c. it's not unimolecular it's bimolecular

    and..

    If you're talking about chlorination of alkAnes then I'm afraid that it most certainly is NOT

    This is a free radical substitution which involves the typical three stages of FR mechanism
    1. Initiation
    2. Propagation
    3. Termination
Updated: May 22, 2005
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