Q.24 A hydrocarbon that undergoes ozonolysis (reaction with ozone followed by reduction with Me2 S)
to form formaldehyde and glyoxal is
Key Concept: Ozonolysis
- Ozonolysis cleaves carbon–carbon double bonds.
- Each carbon of the C=C bond is converted into a carbonyl group.
- Terminal =CH2 group gives formaldehyde (HCHO).
- An internal –CH=CH– unit forms glyoxal (OHC–CHO).
Option-wise Analysis
Option (A): 1,3-Butadiene
This compound contains two conjugated double bonds with terminal CH2 groups.
On ozonolysis:
- Terminal carbons form formaldehyde.
- The internal carbons form glyoxal.
This option gives both formaldehyde and glyoxal. ✅
Option (B)
This structure contains a triple bond or cumulated system.
Ozonolysis of such compounds does not produce glyoxal.
Incorrect option. ❌
Option (C): Benzene
Benzene is an aromatic compound.
Ozonolysis breaks aromaticity and produces a complex mixture of products.
Does not give formaldehyde and glyoxal. ❌
Option (D)
This long-chain diene does not contain the required terminal and internal
alkene arrangement needed to form glyoxal.
Incorrect option. ❌
Final Answer
The hydrocarbon that gives formaldehyde and glyoxal on ozonolysis is
Option (A) – 1,3-Butadiene.
Conclusion
By analyzing the products of ozonolysis, we conclude that only a hydrocarbon
containing terminal and internal double bonds in the correct arrangement can
yield both formaldehyde and glyoxal. Hence, 1,3-butadiene is the correct choice.
