Ozonolysis of an organic compound gives formaldehyde as one of the products. This confirms the presence of:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A terminal CH2= group (as in a vinyl group)
Ozonolysis (ozone, then zinc dust and water) cleaves each C=C double bond, and each carbon of that bond becomes a C=O group. The carbonyl compound formed carries the same groups that its carbon carried in the alkene.
A carbon with two H atoms, the terminal =CH2 group, therefore becomes formaldehyde (\( \ce{HCHO} \)). For example, but-1-ene:
\( \displaystyle \ce{CH3CH2CH=CH2} \xrightarrow[\text{(ii) Zn/}\ce{H2O}]{\text{(i) }\ce{O3}} \ce{CH3CH2CHO + HCHO} \)
Why the other options are incorrect
Option (2) An isopropyl group — Incorrect. An isopropyl group, \( \ce{(CH3)2CH-} \), is saturated; ozonolysis breaks only C=C bonds, so it gives no carbonyl compound from this group.
Option (3) A carbon-carbon triple bond — Incorrect. The carbon of \( \ce{HCHO} \) carries two H atoms; a carbon in a triple bond carries at most one H, so it cannot be the source.
Option (4) Two carbon-carbon double bonds — Incorrect. One terminal C=C is enough, as in but-1-ene; a diene without a =CH2 end, such as hexa-2,4-diene, gives no formaldehyde at all.
NCERT (2026-27 edition):
8.2.1 Preparation of Aldehydes and Ketones – “(i) By ozonolysis of alkenes: As we know, ozonolysis of alkenes followed by reaction with zinc dust and water gives aldehydes, ketones or a mixture of both depending on the substitution pattern of the alkene (Unit 9, Class XI).”