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Chemistry Question 67 – JEE-MAIN 2025

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Given below are two statements: Statement I: Ozonolysis followed by treatment with Zn, H2O of cis-2-butene gives ethanal. Statement II: The product obtained by ozonolysis followed by treatment with Zn, H2O of 3, 6-dimethyloct-4-ene has no chiral carbon atom. In the light of the above statements, choose the correct answer from the options given below

Understand the mechanism of reductive ozonolysis of alkenes, which cleaves the carbon-carbon double bond and forms carbonyl compounds (aldehydes or ketones).

Step 1: Analyze Statement I: Ozonolysis of cis-2-butene✦ Active

The reactant is cis-2-butene, which has the structure CH3−CH=CH−CH3. Reductive ozonolysis (treatment with O3 followed by Zn/H2O) cleaves the carbon-carbon double bond and forms two aldehyde molecules. In this case, the products are CH3−CHO (ethanal) and CH3−CHO (ethanal). Therefore, Statement I is TRUE.

Step 2: Analyze Statement II: Ozonolysis of 3,6-dimethyloct-4-ene○ Expand

The structure of 3,6-dimethyloct-4-ene is CH3−CH2−CHCH3−CH=CH−CHCH3−CH2−CH3. Reductive ozonolysis cleaves the double bond between C4 and C5. This reaction yields two molecules of 3-methylbutanal, with the structure CH3−CH2−CHCH3−CHO. To check for chirality, we examine the carbon atom at position 2 (the one bearing the methyl group). This carbon is bonded to four different groups: −H, −CH3, −CH2CH3, and −CHO. Since all four groups are different, this carbon is a chiral carbon atom. Therefore, the product obtained has a chiral carbon atom. Statement II claims the product has no chiral carbon atom, which makes Statement II FALSE.

Step 3: Conclusion○ Expand

Based on the analysis, Statement I is True and Statement II is False. This corresponds to option 3.

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