Butanone is less reactive than propanal towards nucleophilic addition reactions because:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → more +I effect found in butanone
Butanone (\( \ce{CH3COCH2CH3} \)) is a ketone with two alkyl groups on the carbonyl carbon, whereas propanal (\( \ce{CH3CH2CHO} \)) is an aldehyde with only one. The two alkyl groups push electrons towards the carbonyl carbon (+I effect), reducing its partial positive charge, and they also crowd the carbon (steric hindrance). Butanone is therefore less reactive than propanal towards nucleophilic addition.
Why the other options are incorrect
Option (2) less +I effect found in butanone — Incorrect. Butanone has more, not less, +I effect, because it has two alkyl groups.
Option (3) more +I effect found in propanal — Incorrect. Propanal has only one alkyl group, so its +I effect is smaller; a larger +I effect in propanal would make it the less reactive one.
Option (4) less +ve charge found on carbonyl group of propanal — Incorrect. The carbonyl carbon of propanal carries more positive charge than that of butanone, which is why propanal is the more reactive.
NCERT (2026-27 edition):
Nucleophilic Addition Reactions – …
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | – | – | 02-06 S3 31-05 S1 | – |