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Electrophilic Addition Mechanism

  1. Oct 24, 2008 #1
    1. The problem statement, all variables and given/known data

    Show the complete mechanism for the electrophilic addition reaction of toluene and bromine, isopropylbenzene and bromine. Draw the structure of the intermediate hydrocarbon.

    2. Relevant equations

    None

    3. The attempt at a solution

    I am having a really hard time with this question, I understand how electrophilic addition works in alkenes, and have reviewed electrophilic substitution reaction mechanisms in molecules with benzene rings.

    For the toluene

    [​IMG]

    would the bromine firstly seperate to form two seperate bromine ions, and then would one bromine attack the top most hydrogen, forming CH2BR instead of CH3, the remaining Br combine with the free H ion to form HBR??

    thanks
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 24, 2008 #2

    GCT

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    From what I remember it is more of a concerted radical mechanism.
     
  4. Oct 24, 2008 #3

    chemisttree

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    If you are talking about electrophilic bromination, you are going to brominate the aromatic ring.
     
  5. Oct 24, 2008 #4

    GCT

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    That does not seem to happen without a catalyst. This is probably electrophilic addition and not electrophilic aromatic substitution.
     
  6. Oct 24, 2008 #5

    chemisttree

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    It would be substitution for the benzylic bromination as well... free radical substitution. Benzylic bromination with Br2 requires a catalyst as well although you could do it at high enough temperature to avoid the catalyst. The question didn't preclude the use of catalysts.

    Addition reactions using bromine are typically ones that add Br2 across a double bond, although not in aromatic systems like toluene. Thus, Br2 is added to the structure of the reactant whereas the substitution of hydrogen (whether aromatic or benzylic or aliphatic) by bromne is properly identified as an electrophilic substitution reaction.
     
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