Consider the following statements about the reactions of aldehydes and ketones due to α-hydrogen.
(A) The acidity of α-hydrogen atoms of carbonyl compounds is due to the strong electron withdrawing effect of the carbonyl group and resonance stabilisation of the conjugate base.
(B) The name aldol is derived from the names of the two functional groups, aldehyde and alcohol, present in the products.
(C) Aldehydes and ketones having at least one α-hydrogen undergo the aldol reaction in the presence of concentrated alkali as catalyst.
(D) Though ketones give ketols, the general name aldol condensation still applies to the reactions of ketones.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B) and (D) only
An α-hydrogen is a hydrogen on the carbon next to the carbonyl group. Because it is acidic, a base can remove it, and this starts the aldol reaction.
(A) The acidity of α-hydrogen atoms of carbonyl compounds is due to the strong electron withdrawing effect of the carbonyl group and resonance stabilisation of the conjugate base. — True. The C=O group pulls electrons away, and the negative charge left after the proton is removed is spread by resonance onto the oxygen atom.
(B) The name aldol is derived from the names of the two functional groups, aldehyde and alcohol, present in the products. — True. A product such as 3-hydroxybutanal has both an –CHO group (ald-) and an –OH group (-ol).
(C) Aldehydes and ketones having at least one α-hydrogen undergo the aldol reaction in the presence of concentrated alkali as catalyst. — False. The aldol reaction uses dilute alkali as the catalyst. Heating with concentrated alkali is the condition for the Cannizzaro reaction of aldehydes that have no α-hydrogen.
(D) Though ketones give ketols, the general name aldol condensation still applies to the reactions of ketones. — True. A ketol has a keto group and an alcohol group, but the reaction of ketones is similar to that of aldehydes, so the same name is used.
NCERT (2026-27 edition):
8.4 Chemical Reactions – “The acidity of α-hydrogen atoms of carbonyl compounds is due to the strong electron withdrawing effect of the carbonyl group and resonance stabilisation of the conjugate base.”
“(i) Aldol condensation: Aldehydes and ketones having at least one α-hydrogen undergo a reaction in the presence of dilute alkali as catalyst to form β-hydroxy aldehydes (aldol) or β-hydroxy ketones (ketol), respectively. This is known as Aldol reaction.”
“The name aldol is derived from the names of the two functional groups, aldehyde and alcohol, present in the products. … Though ketones give ketols (compounds containing a keto and alcohol groups), the general name aldol condensation still applies to the reactions of ketones due to their similarity with aldehydes.”