Orgo Question

[egan]

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When can you tell when OH- attacks the carbonyl group versus performing an aldol condensation? For example, how do you know that acetic acid(propanone) doesn't get attacked by OH- and instead gets deprotonated at its alpha carbon? Hope this makes sense🙂

 

[mh0000]

I don't think acetic acid(or any carboxylic acid) readily forms an enolate ion due to the acid-base behavior of the carb. acid and the base. Also, OH- attacking the carbonyl will not result in any net effect.

 

[needzmoar]

When can you tell when OH- attacks the carbonyl group versus performing an aldol condensation? For example, how do you know that acetic acid(propanone) doesn't get attacked by OH- and instead gets deprotonated at its alpha carbon? Hope this makes sense🙂

I think you mean acetone, right? Well here's the thing. If OH attacks the carbonyl, you get a hydrated specie that's labile and will readily convert back to the ketone. If it under goes aldol followed by dehydration the Keq will favor the conjugated product. Typically, if you see a ketone with no other function group, it's probably gonna be the aldol.

 

[needzmoar]

Also, OH- attacking the carbonyl will not result in any net effect.

true dat

 

[mh0000]

Yes, I think he means acetone. Like needz said, the equilibirum does not favor a gem diol product with the nucelophilic attack on the carbonyl due to steric reasons. Keep in mind that for aldol reactions, only a catalytic amount of base is needed. Concentrated base solutions will lead to heavy enolate formation, which itself reduces the electrophilicity of the carbonyl towards an aldol reaction.

 

[Troyvdg]

I don't think acetic acid(or any carboxylic acid) readily forms an enolate ion due to the acid-base behavior of the carb. acid and the base. Also, OH- attacking the carbonyl will not result in any net effect.

+1
OH attacking a carboxylic acid will deprotinate it forming a carboxylate