NEET 2020 · ChemistrySelf-aldolPrevious Year Question
The reaction between benzaldehyde and acetophenone in the presence of dilute NaOH is known as:
Answer: (B) (B) Cross aldol condensation. \textbf{Answer:} (B) Cross aldol condensation \textbf{Solution:} Benzaldehyde has no alpha-hydrogen, while acetophenone has alpha-hydrogens.
- A.(A) Cross Cannizzaro's reaction
- B.(B) Cross aldol condensation✓
- C.(C) Aldol condensation
- D.(D) Cannizzaro's reaction
Correct Answer
(B) (B) Cross aldol condensation
Solution & Explanation
\textbf{Answer:} (B) Cross aldol condensation \textbf{Solution:} Benzaldehyde has no alpha-hydrogen, while acetophenone has alpha-hydrogens. Under dilute NaOH, the alpha-carbon of acetophenone adds to the carbonyl of benzaldehyde and, on dehydration, gives the alpha,beta-unsaturated ketone (chalcone). Since two different carbonyl compounds (an aldehyde and a ketone) react, it is a cross (mixed) aldol condensation.
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