(x) • He thought of preparing the molecule using an aldol condensation reaction. He found a few cyclic alkenes in his laboratory. He thought of performing ozonolysis reaction on alkene to produce a dicarbonyl compound followed by aldol reaction to prepare "x". Predict the suitable alkene that can lead to the formation of "x".
(A)(see structure)✓ Correct
(B)(see structure)
(C)(see structure)
(D)(see structure)
Answer: (A)
Solution
Ozonolysis of 1-methylcyclohexene cleaves the ring double bond to give an open-chain dicarbonyl compound carrying an aldehyde group at one end and a methyl ketone at the other, joined by the remaining chain of the original ring.
Under basic conditions (OH−,Δ), the enolate generated alpha to the ketone carbon attacks the aldehyde carbon intramolecularly. The resulting β-hydroxy carbonyl intermediate dehydrates to close a five-membered ring bearing an exocyclic acetyl (−COCH3) group conjugated with the ring double bond — the target molecule x.
Only 1-methylcyclohexene gives, on ozonolysis, a dicarbonyl compound with the chain length and substitution pattern needed to cyclise to this product on intramolecular aldol condensation; the other cyclic alkenes offered would give dicarbonyls of the wrong ring size or substitution pattern.
The suitable starting alkene is 1-methylcyclohexene.
JEE Main · 2025 · 24 Jan 2025 · Shift 1 · Single correct option
