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.
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.
Sorry, i meant the same, i don't know what made me to write that.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.