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Birch reduction

  1. Sep 18, 2012 #1
    1. The problem statement, all variables and given/known data
    2zzqddd.png

    2. Relevant equations



    3. The attempt at a solution
    I thought the answer should be this:
    w7buk3.png
    But in the answer key, its something else. In the answer key, it is:
    2czbxu9.png
    I don't understand why the left ring doesn't react.
     
  2. jcsd
  3. Sep 18, 2012 #2

    AGNuke

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    What does -CN do?

    HINT: Try making resonating structures involving -CN.
     
    Last edited: Sep 18, 2012
  4. Sep 18, 2012 #3
    It has an electron withdrawing effect.
     
  5. Sep 18, 2012 #4
    How will that help me here?
     
  6. Sep 19, 2012 #5

    AGNuke

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    What's the first step of Birch Reduction? Donation of electron from Sodium Atom. If my memory serves right, I think those carbon atoms which suffers from shortage of electrons will be able to accept that electron, in this case, the ring attached to -CN group.

    I said to try making the resonating structures to get yourself the idea of effective electronic distribution in the compound.

    For your sake, this question I solved it via Mechanism. Reality is I didn't know Birch Reduction, or any reduction for God's sake. I was only able to attempt this question because I saw its Mechanism afterward.

    Sodium atom is donating an electron, so try getting that electron accepted where -CN can exhibit its -M effect.
     
  7. Sep 19, 2012 #6
    Okay, i get it, you mean that the electron would stay in the right ring most of the times during resonance and that's why the right ring reacts. Thanks! :smile:

    But what if i deliberately wanted to reduce the left ring? Which reagent should i be using?
     
    Last edited: Sep 19, 2012
  8. Sep 19, 2012 #7

    AGNuke

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    Err... I meant the right ring is in electron debt due to -CN and that's why the lone electron from Sodium atom will be accepted by atoms bossed by -CN.

    And another thing, you don't destroy aromaticity completely, especially when you are getting Benzene if you are given some workaround, in this case, electron withdrawing group.

    Like I said, I don't know about Reduction. If I have to guess, then the reducing agent must be the one which do not donate the electron in the first step and has the capability to reduce alkenes.
     
  9. Sep 19, 2012 #8
    Sorry, i meant the same, i don't know what made me to write that. :redface:

    I think i need to find the answer on my own for my self made question. :smile:
     
  10. Sep 19, 2012 #9

    AGNuke

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    To the second question, I don't think there's a reducing agent capable of doing so. If you want to make the second compound, replace the -CN with donor group and re-replace it.
     
  11. Sep 19, 2012 #10
    Yes, that should do the trick, thanks! :smile:
     
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