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Birch reduction

  • Thread starter Saitama
  • Start date
  • #1
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Homework Statement


2zzqddd.png


Homework Equations





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.
 

Answers and Replies

  • #2
AGNuke
Gold Member
455
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What does -CN do?

HINT: Try making resonating structures involving -CN.
 
Last edited:
  • #3
3,812
92
What does -CN do?
It has an electron withdrawing effect.
 
  • #4
3,812
92
HINT: Try making resonating structures involving -CN.
How will that help me here?
 
  • #5
AGNuke
Gold Member
455
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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.
 
  • #6
3,812
92
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.
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:
  • #7
AGNuke
Gold Member
455
9
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.
 
  • #8
3,812
92
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.
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:
 
  • #9
AGNuke
Gold Member
455
9
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.
 
  • #10
3,812
92
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.
Yes, that should do the trick, thanks! :smile:
 

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