Alpha-hydrogen reactivity; aldol condensation and Cannizzaro reaction — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Which carbon atom in a carbonyl compound is called the alpha-carbon?

• A. The carbon atom of the carbonyl group
• B. The carbon atom directly adjacent to the carbonyl carbon
• C. The carbon atom farthest from the carbonyl group
• D. Any carbon atom bonded to oxygen

Question 2 · difficulty L2 · understanding

Which of the following carbonyl compounds does not contain any alpha-hydrogen?

• A. Ethanal, $\text{CH}_3\text{CHO}$
• B. Propanone, $\text{CH}_3\text{COCH}_3$
• C. Benzaldehyde, $\text{C}_6\text{H}_5\text{CHO}$
• D. Propanal, $\text{CH}_3\text{CH}_2\text{CHO}$

Question 3 · difficulty L2 · understanding

Which condition is essential for an aldehyde or ketone to undergo self-aldol reaction?

• A. It must contain at least one alpha-hydrogen
• B. It must contain a benzene ring
• C. It must contain two carbonyl groups
• D. It must contain no alpha-hydrogen

Question 4 · difficulty L2 · understanding

Which aldehyde is most characteristically expected to undergo Cannizzaro reaction in concentrated alkali?

• A. Ethanal
• B. Propanal
• C. Benzaldehyde
• D. Butanal

Question 5 · difficulty L3 · application

Ethanal is treated with dilute sodium hydroxide at low temperature. What is the initial aldol addition product?

• A. But-2-enal
• B. 3-Hydroxybutanal
• C. Butan-2-one
• D. Ethanoic acid

Question 6 · difficulty L3 · application

On heating the aldol formed from ethanal, which major product is obtained by dehydration?

• A. But-2-enal
• B. Butan-1-ol
• C. Butane-1,3-diol
• D. Ethyl ethanoate

Question 7 · difficulty L3 · application

Which pair of products is formed when benzaldehyde undergoes Cannizzaro reaction with concentrated sodium hydroxide?

• A. Benzyl alcohol and sodium benzoate
• B. Benzoic acid and benzene
• C. Benzyl alcohol and phenol
• D. Sodium benzoate and acetophenone

Question 8 · difficulty L3 · application

Which of the following compounds can undergo self-aldol condensation under suitable basic conditions?

• A. Methanal
• B. Benzaldehyde
• C. Propanone
• D. 2,2-Dimethylpropanal

Question 9 · difficulty L4 · application

A mixture contains ethanal and benzaldehyde. Which statement best predicts their behavior toward dilute base under aldol conditions?

• A. Both can independently form enolates and both undergo self-aldol reaction
• B. Only ethanal can form an enolate; it can react with benzaldehyde as the carbonyl electrophile
• C. Only benzaldehyde can form an enolate; ethanal acts only as the electrophile
• D. Neither can participate because two different aldehydes cannot undergo aldol reaction

Question 10 · difficulty L4 · application

An aldehyde $X$ gives a positive Tollens' test, does not undergo self-aldol reaction, and on treatment with concentrated sodium hydroxide gives an alcohol and a carboxylate salt. Which compound is consistent with these observations?

• A. Ethanal
• B. Propanal
• C. Benzaldehyde
• D. Butanal