Two isomers 'A' and 'B' with molecular formula $\mathrm{C}_{4}\mathrm{H}_{8}$ give different products on oxidation with $\mathrm{KMnO}_{4}$ in acidic medium. Isomer 'A' on reaction with $\mathrm{KMnO}_{4}/\mathrm{H}^{+}$ results in effervescence of a gas and gives ketone. The compound 'A' is

JEE Main · 2022 · 29 Jun 2022 · Shift 1 · Hydrocarbons

Two isomers 'A' and 'B' with molecular formula

C_{4} H_{8}

give different products on oxidation with

KMnO_{4}

in acidic medium. Isomer 'A' on reaction with

KMnO_{4} / H^{+}

results in effervescence of a gas and gives ketone. The compound 'A' is

(A)But-1-ene
(B)cis-But-2-ene
(C)trans-But-2ene
(D)2-methyl propene✓ Correct

Answer: (D)

Solution

The key observation is that isomer A produces effervescence (gas evolution) and a ketone upon oxidation with

KMnO_{4} / H^{+}

. 2-methylpropene has a terminal double bond with two methyl groups on one carbon. Oxidation cleaves the double bond: the terminal

CH_{2}

is oxidized to

CO_{2}

(causing effervescence), while the other carbon bearing two methyl groups forms acetone (a ketone). But-1-ene would give a carboxylic acid, not a ketone. The cis/trans-but-2-ene isomers would give carboxylic acids. Therefore, the answer is (D) 2-methyl propene.

JEE Main · 2022 · 29 Jun 2022 · Shift 1 · Single correct option

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JEE Main · 2022 · 29 Jun 2022 · Shift 1 · Hydrocarbons

Solution

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