Given below are two statements :
Statements I : Acidity of α-hydrogens of aldehydes and ketones is responsible for Aldol reaction.
Statement II : Reaction between benzaldehyde and ethanal will NOT give Cross - Aldol product.
In the light of the above statements, choose the most appropriate answer from the options given below :

Solution

Chemistry ma’am · 4 steps

Ethanal has α-hydrogens even if benzaldehyde does not, and one partner with α-H is enough for a cross aldol.

1. Statement I. An α-hydrogen sits next to the C=O group and is acidic, because the enolate left after a base removes it is stabilised by resonance. That enolate attacks a second carbonyl carbon, which is the aldol reaction. So Statement I is correct.
2. Check each partner. Benzaldehyde, C₆H₅CHO, has no α-hydrogen, so it cannot form an enolate. It can still act as the carbonyl that gets attacked. Ethanal, CH₃CHO, has three α-hydrogens, so it supplies the enolate.

   C₆H₅CHO + CH₃CHO →(dil. NaOH) C₆H₅CH(OH)CH₂CHO →(Δ, -H₂O) C₆H₅CH=CHCHO

3. Statement II. The enolate of ethanal adds to benzaldehyde to give a cross aldol product, which dehydrates to cinnamaldehyde. This is the Claisen–Schmidt reaction. So Statement II is incorrect.
4. So. Statement I is correct and Statement II is incorrect, which is option (b).

The idea to keep. For a cross aldol, only one of the two carbonyls needs an α-hydrogen. The one without α-H acts as the electrophile, which is why benzaldehyde works so well in the Claisen–Schmidt reaction.

Answer from the NTA final answer key. Solution by PrepWiser.