Crossed aldol condensation is done between acetaldehyde and acetophenone by using NaOH as the base. So, here we can get 4 possible products. But which one would be the major?

I know that acetaldehyde will act as electrophile to which addition will occur. But what will act as nucleophile to give major product: acetaldehyde or acetophenone?

I don't have any solid reasoning whether acetaldehyde enolate or acetophenone enolate will give major product with acetaldehyde.

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    $\begingroup$ The so called 'cross aldol condensation' between a ketone and an aldehyde is actually called 'claisen-schmidt condensation' $\endgroup$ – Carrick Jan 11 '19 at 7:22
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    $\begingroup$ And for the answer... it's generally easier for a nucleophile to attack on an aldehyde as compared to a ketone (steric and polar factors both can be used to explain that) $\endgroup$ – Carrick Jan 11 '19 at 7:24
  • $\begingroup$ All the reactions leading to the 4 possible products are reversible so you will get the thermodynamic product. $\endgroup$ – Waylander Jan 11 '19 at 7:32
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    $\begingroup$ @Carrick i know that neucleophile attack on aldehyde is better. But my question is which is better nucleophilic aldehyde or acetophenone enolate. $\endgroup$ – ATHARVA Jan 11 '19 at 8:04
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    $\begingroup$ @Waylander But which out of the 4 is thermodynamic that is more stable product. $\endgroup$ – ATHARVA Jan 11 '19 at 8:05

I would expect the aldehyde to be the major electrophile in this reaction. The reason is that the steric demands for a nuelophile coming close to the carbonyl carbon are lower than for the same nucelophile coming close to a ketone.

I would expect that the enolate formed from the reaction of the methyl phenyl ketone (acetopheone) to be slightly more stable than the one formed from ethanal. This is because the enolate can be delocalised into the benzene ring.

If we were to form the enolate from ethanal then if this was to attack the carbonyl carbon of acetophenone then we would get a tertary alcohol as the product. The major aldo product in this reaction will be a secondary alcohol formed by the action of the enolate from acetopheone on the ethanal.


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