1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Organic Chemistry Mechanism Question

  1. Apr 25, 2009 #1
    1. The problem statement, all variables and given/known data
    I am given isobutane as my starting material, Br2 and benzoyl peroxide as my radical initiators. My final product is the isobutane with Br attached instead of H.

    I have to design the mechanism. I have tried what seems like an endless combination of mechanism attempts, and can't seem to get it. I do not have to include the termination steps, only the initiation and propagation steps.

    3. The attempt at a solution
    -I homolyzed the Br atom and the benzoyl peroxide at the same time in step one.
    -In step two, I took one of the benzoyl peroxide radicals and attempted to remove the H from isobutane creating a radical off the alkyl group.
    -In step three, I homolyzed another Br2 molecule added it onto the isobutane radical.
    -In step four, I didn't know what to do.

    Evidently I have my steps all screwed up. I don't know when I'm supposed to homolyze the peroxide and then what I'm supposed to do with it. Any help would be greatly appreciated.
     
  2. jcsd
  3. Apr 25, 2009 #2
    i never came across benzoyl peroxide. I would suggest that it would break Br2 into Br+ and Br-. The Br+ is accepted by the benzene ring (electrophilic substitution rxn) and the Br- would attack the hydrocarbon as a radical.

    but i really don't know.
     
  4. Apr 28, 2009 #3

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    In isobutane you have three methyl groups and one methine. That is a 9:1 ratio of primary substitution vs tertiary. One would think that you would get a 9:1 ratio of the 1-bromo product relative to the 2-bromo product but remember that bromine is less reactive than chlorine in free radical radical reactions and is much more selective.

    Benzoyl peroxide can be thought of as a free radical initiatiator (like you would think of heat or light in that regard). Which bond (C-H vs. Br-Br) is most likely to homolytically cleave in the first step of your mechanism?

    Hint: Look at the bond energies of these two types of bonds.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Organic Chemistry Mechanism Question
Loading...