JEE Advanced 2022 Paper 2, Chemistry Section 1 Q7: Aromatic Hydrocarbons: Benzene

JEE Advanced2022Paper 2Chemistry Section 1

The number of -CH $_{2}$ - (methylene) groups in the product formed from the following reaction sequence is ________.

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Solution

Step 1: Reductive ozonolysis of (E)-oct-4-ene cleaves the central C=C to give two equivalents of butanal (CH $_{3}$ CH $_{2}$ CH $_{2}$ CHO).

Step 2: KMnO $_{4}$ oxidises butanal to butanoic acid (CH $_{3}$ CH $_{2}$ CH $_{2}$ COOH).

Step 3: Kolbe electrolysis of sodium butanoate couples two alkyl radicals (decarboxylative dimerisation) to give hexane (CH $_{3}$ CH $_{2}$ CH $_{2}$ CH $_{2}$ CH $_{2}$ CH $_{3}$ ).

Step 4: Cr $_{2}$ O $_{3}$ at 770 K, 20 atm is the aromatisation (dehydrocyclisation) catalyst that converts $n$ -hexane to benzene.

Benzene contains six aromatic CH groups and zero $-$ CH $_{2} -$ (methylene) groups.

$∴$ Number of methylene groups = 0.

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JEE Advanced 2022 Paper 2, Chemistry Section 1 Q7: Aromatic Hydrocarbons: Benzene

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