Why Doesn't the Left Ring React in Birch Reduction?

[Saitama]

Homework Statement

Homework Equations

The Attempt at a Solution

I thought the answer should be this:

But in the answer key, its something else. In the answer key, it is:

I don't understand why the left ring doesn't react.

 

[AGNuke]

What does -CN do?

HINT: Try making resonating structures involving -CN.

 

[Saitama]

What does -CN do?

It has an electron withdrawing effect.

 

[Saitama]

HINT: Try making resonating structures involving -CN.

How will that help me here?

 

[AGNuke]

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.

 

[Saitama]

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!

But what if i deliberately wanted to reduce the left ring? Which reagent should i be using?

 

[AGNuke]

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.

 

[Saitama]

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.

I think i need to find the answer on my own for my self made question.

 

[AGNuke]

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.

 

[Saitama]

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!