Where Does the α-Hydrogen Abstraction Occur in a Ketone-Ester Reaction?

[Saitama]

Homework Statement

(see attachment)

Homework Equations

The Attempt at a Solution

It looks to me a type of Claisen condensation but i did not realize it until i checked my book.
Before checking the book, i tried to do it by thinking on what is given in the question. We have a ethoxide ion here which acts as a base. It will probably abstract an α-hydrogen but from where? We have a ketone and an ester and both have acidic α-hydrogens. Please help me in understanding that from where the α-hydrogen is abstracted.

I have one more question (this may be a stupid one like the one above), can ethoxide ion directly attack carbonyl group present in any of the reactant? This would lead to breaking of double between carbon and oxygen towards oxygen but if i continue with this, i reach nowhere to the answer.

 

[Saitama]

Anyone?

 

[chemisttree]

I was taught that you should determine which alpha hydrogen is the most acidic.

 

[ChiralWaltz]

If using NaOC2H5 to attack a carbonyl group gets you nowhere, you shouldn't do it. What is the 1st thing that happens in a Claisen Condensation mechanism?

 

[Saitama]

I was taught that you should determine which alpha hydrogen is the most acidic.

What i think is that α-hydrogen gets abstracted from the ester because of more resonating structures formed after its abstraction. Is this right?

 

[ChiralWaltz]

Running it with the ester as the reacting enolate gives me some weird molecule that I don't know what to do with. If only that ring was aromatic. Sorry I'm unable to be of assistance.

 

[AGNuke]

According to me, the answer should be C. I hope that to be right, considering I read Claisen Condensation just 5 minutes ago.

 

[Saitama]

Indeed, the answer is C, the mechanism for Claisen condesation starts with the abstraction of alpha-hydrogen from ketone but this doesn't make sense to me, why not ester? More resonating structures are formed when hydrogen is abstracted from ester.

 

[ChiralWaltz]

I got answer C also. Wouldn't that require using the carbonyl and methyl on the aliphatic ring to act as the enolate? Doesn't the aliphatic ring provide no resonance since each site has a full octet and cannot accommodate the lone electron pair on the ring?

 

[AGNuke]

More resonating structures are formed when hydrogen is abstracted from ester.

I don't think so. The oxygen in -O-Et is no way involved in resonance if your notions are as such. I followed the mechanism given at Wikipedia and got the answer.

 

[Saitama]

The oxygen in -O-Et is no way involved in resonance...

Why?

 

[AGNuke]

Try drawing the resonance structure. There is no "significant" resonance, I should've added, at that O atom.

 

[Saitama]

Try drawing the resonance structure. There is no "significant" resonance, I should've added, at that O atom.

Agreed but what about the inductive effect of O in OEt? Doesn't that play any role?

 

[chemisttree]

Try this.

 

[Saitama]

Try this.

Thanks chemisttree, that's exactly what i am looking for.