Identify the product in the following reaction.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Hexane-1,6-dioic acid (adipic acid), HOOC–(CH2)4–COOH
Hot acidified potassium permanganate is a strong oxidising agent. It breaks the C=C double bond of an alkene, and each doubly bonded carbon that carries a hydrogen is oxidised to a –COOH group. In cyclohexene the double bond is in a ring, so cleavage opens the ring and gives a straight chain of six carbons with a carboxyl group at each end:
Cyclohexene + [O] (\( \ce{KMnO4} \)/\( \ce{H2SO4} \), Δ) → \( \ce{HOOC-CH2CH2CH2CH2-COOH} \)
The product is adipic acid (hexanedioic acid), the monomer used for nylon-6,6.
Why the other options are incorrect
Option (1) \(CO_2+H_2O\) — Incorrect. This would be complete combustion; \( \ce{KMnO4} \) cleaves the double bond but does not burn the whole molecule.
Option (2) Cyclohexene-1,2-dicarboxylic acid — Incorrect. A cyclohexene-1,2-dicarboxylic acid would need two extra carbon atoms; oxidation cannot add carbons, and the ring would not survive with its double bond intact.
Option (4) Cyclohexane + CO2 + H2O — Incorrect. Cyclohexane is the reduction (hydrogenation) product of cyclohexene, not an oxidation product.
NCERT (2026-27 edition):
Methods of Preparation of Carboxylic Acids – “Example 8.5 Write chemical reactions to affect the following transformations: … (v) Cyclohexene to hexane-1,6-dioic acid … Solution”
