Aldehydes and Ketones, having at least one methyl group linked to the carbonyl carbon atom (methyl Ketones), are oxidised by sodium hypohalite to sodium salts of corresponding carboxylic acids having one carbon atom less than that of carbonyl compound is converted to haloform. This oxidation does not affect a carbon–carbon double bond, if present in a molecule.
Arrange in decreasing order of nucleophilic addition:
(A) \(CH_3CHO\)
(B) \(C_2H_5COCH_3\)
(C) \(CH_3COCH_3\)
(D) \(HCHO\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (D) > (A) > (C) > (B)
Reactivity towards nucleophilic addition depends on two factors:
Steric: larger groups round the carbonyl carbon hinder the approach of the nucleophile.
Electronic: alkyl groups release electrons (+I) and reduce the positive charge on the carbonyl carbon.
Both factors favour fewer and smaller alkyl groups:
(D) HCHO — no alkyl group: most reactive.
(A) CH3CHO — one methyl group (aldehyde).
(C) CH3COCH3 — two methyl groups (ketone).
(B) C2H5COCH3 — a methyl and a larger ethyl group: least reactive.
Shortcut: Options (1) and (2) both begin (D) > (A); acetone is less hindered than butanone, so (C) comes before (B): Option (1).
Note: It seems that there is a mistake in the original NTA paper, which prints “… than that of carbonyl compound is converted to haloform” when it should read “… than that of carbonyl compound. The methyl group is converted to haloform”.
NCERT (2026-27 edition):
Reactivity
