See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: The reaction of benzene with a four-membered cyclic ether (oxetane) under strong acid (H2SO4) proceeds via acid-catalyzed ring opening of the oxetane to generate a carbocation, which then undergoes Friedel-Crafts-type alkylation of benzene, followed by an intramolecular cyclization. Step 1 – Identify the product: The product is 1,1,4,4-tetramethyl-1,2,3,4-tetrahydronaphthalene. This is a tetralin (benzene fused to a cyclohexane ring) where both C1 and C4 of the cyclohexane ring bear two methyl groups (gem-dimethyl at each bridgehead carbon adjacent to the aromatic ring). Step 2 – Retrosynthetic analysis: The saturated ring contains 4 carbons (C1–C4) fused to benzene. C1 carries two methyls and is bonded to the benzene ring; C4 also carries two methyls and is bonded to the benzene ring. The chain connecting the two aromatic carbons is –C(CH3)2–CH2–CH2–C(CH3)2–, i.e., a 4-carbon tether with gem-dimethyl groups at both ends. Step 3 – Forward reaction with option (c), 2,2-dimethyloxetane: 2,2-Dimethyloxetane is a four-membered ring: O–CH2–CH2–C(CH3)2 (oxygen at position 1, gem-dimethyl at C2 relative to the C–O bond on the substituted carbon). Under H2SO4, the oxetane ring opens to give a carbocation at the more substituted carbon: (CH3)2C+–CH2–CH2–OH (or the protonated oxetane opens to give tertiary carbocation). This tertiary carbocation attacks benzene (Friedel-Crafts alkylation) to give (CH3)2C(Ph)–CH2–CH2–OH. The terminal –OH is protonated by H2SO4 to give a second carbocation (CH3)2C(Ph)–CH2–CH2+, which undergoes intramolecular Friedel-Crafts cyclization onto the benzene ring, giving the 1,1,4,4-tetramethyltetralin product after loss of proton. This perfectly accounts for the gem-dimethyl groups at both C1 and C4. Step 4 – Why other options fail: (a) Succinic anhydride would give a Friedel-Crafts acylation product (a keto-acid), not a tetramethyltetralin. (b) 2,3-Dimethyloxetane would give only one gem-dimethyl group per carbon upon ring opening, yielding a 1,2-dimethyl or 1,3-dimethyl substituted tetralin, not 1,1,4,4-tetramethyl. (d) The dicarboxylic acid would require a Haworth synthesis-type approach giving a keto or hydroxy intermediate, not the fully reduced tetramethyltetralin directly under H2SO4 alone. Therefore, the correct answer is C.