JEE Main 2026 — Hydrocarbons Question with Solution
JEE Main 2026 (05 April Shift 1)
Question
"P" is a hydrocarbon of molecular formula: CH. On ozonolysis, "P" forms "Q". "Q" on treatment with alkali under reflux condition produces "R", which on treatment with I/NaOH gives a yellow precipitate. Acidification of the solution gives "S". The structure of "S" is given below:
The correct structure of "P" is
The correct structure of "P" is
Choose an option
Show full solutionCorrect option: D
Correct answer
D
Step-by-step explanation
The structure of "S" is 2-methylcyclopent-1-ene-1-carboxylic acid.
Since "S" is obtained by the acidification of the product from the iodoform reaction of "R", "R" must contain a methyl ketone group (). The iodoform reaction converts the group into a group alongside the formation of a yellow precipitate of iodoform (). Therefore, the structure of "R" is 1-acetyl-2-methylcyclopentene.
"R" is formed by the intramolecular aldol condensation of "Q". Performing a retro-aldol condensation on "R" by cleaving the double bond in the cyclopentene ring yields octane-2,7-dione as "Q" ().
"Q" is obtained by the ozonolysis of "P". To determine the structure of "P", we perform retro-ozonolysis by removing the oxygen atoms from the two carbonyl groups of "Q" and connecting the corresponding carbon atoms with a double bond. Connecting the C2 and C7 carbons forms a six-membered ring with methyl groups at the double bond.
Thus, "P" is 1,2-dimethylcyclohexene.
Answer:
Since "S" is obtained by the acidification of the product from the iodoform reaction of "R", "R" must contain a methyl ketone group (). The iodoform reaction converts the group into a group alongside the formation of a yellow precipitate of iodoform (). Therefore, the structure of "R" is 1-acetyl-2-methylcyclopentene.
"R" is formed by the intramolecular aldol condensation of "Q". Performing a retro-aldol condensation on "R" by cleaving the double bond in the cyclopentene ring yields octane-2,7-dione as "Q" ().
"Q" is obtained by the ozonolysis of "P". To determine the structure of "P", we perform retro-ozonolysis by removing the oxygen atoms from the two carbonyl groups of "Q" and connecting the corresponding carbon atoms with a double bond. Connecting the C2 and C7 carbons forms a six-membered ring with methyl groups at the double bond.
Thus, "P" is 1,2-dimethylcyclohexene.
Answer:
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This is a previous-year question from JEE Main 2026, covering the Hydrocarbons chapter of Chemistry. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.