Aldol condensation question

[GBP12]

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When doing the reaction, lets say you have an aldehyde and a ketone, how do you decide which one attacks the other? I mean they both have carbons with hydrogens coming off the carbonyl carbon...

I ask because in Chad's reaction list he has the ketone adding to the aldehyde and I don't know why.

 

[DAT Destroyer]

When doing the reaction, lets say you have an aldehyde and a ketone, how do you decide which one attacks the other? I mean they both have carbons with hydrogens coming off the carbonyl carbon...

I ask because in Chad's reaction list he has the ketone adding to the aldehyde and I don't know why.

You must be careful here,,,,,,If both compounds have ALPHA hydrogens........GOOD LUCK......you are left with a mess.

If you have acetone......for example....and Benzaldehyde.......this will work. Only one reactant should have an alpha hydrogen for success. It is called a Mixed Aldol. The base reacts with the ketone,,,,,to generate the enolate anion......which acts as a nucleophile,,,,,to attack the aldehyde,,,,,to finish the job.

RESULT ? A beta hydroxy carbonyl compound. Consult any Standard text such as Wade, Carey, or Klein for details.

Hope this helps

Dr. Romano

 

[GBP12]

You must be careful here,,,,,,If both compounds have ALPHA hydrogens........GOOD LUCK......you are left with a mess.

If you have acetone......for example....and Benzaldehyde.......this will work. Only one reactant should have an alpha hydrogen for success. It is called a Mixed Aldol. The base reacts with the ketone,,,,,to generate the enolate anion......which acts as a nucleophile,,,,,to attack the aldehyde,,,,,to finish the job.

RESULT ? A beta hydroxy carbonyl compound. Consult any Standard text such as Wade, Carey, or Klein for details.

Hope this helps

Dr. Romano

Thanks that definitely clears it up, if only one compound can have an alpha hydrogen that makes the problem pretty easy.

 

[cacajuate]

Be careful if heat is added or not in the last step. No heat=have a hydroxl, heat=double bond.