See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Acid-catalyzed intramolecular aldol condensation and/or acid-catalyzed enolization and dehydration leading to aromatization of a bicyclic enone. Step 1 - Identify the starting material: The starting material is 8a-methyl-3,4,8,8a-tetrahydronaphthalenone (an octalone), which is a bicyclic compound consisting of a cyclohexanone ring bearing an alpha,beta-unsaturation (enone) fused to a cyclohexane ring, with a methyl group at the ring junction (C8a). Step 2 - Reaction with acid (H+): Under acidic conditions, this type of bicyclic enone undergoes acid-catalyzed isomerization. The key process here is the acid-catalyzed tautomerization/dehydration sequence. The enone system in ring A (the cyclohexenone) can undergo repeated enolization steps under acidic conditions. The cross-conjugated enone can tautomerize toward a phenol (complete aromatization of ring A) via sequential dehydration steps driven by the thermodynamic stability of the aromatic product. Step 3 - Aromatization pathway: The bicyclic enone loses water (or undergoes proton shifts) to give a partially aromatic intermediate, ultimately yielding a product where ring A becomes aromatic (benzene ring) while ring B (the cyclohexane ring) retains the methyl group at the ring junction. The methyl group at the ring junction migrates or is retained as a substituent on the aromatic ring. The product is a tetrahydronaphthalene (tetralin) derivative with a hydroxyl group on the aromatic ring - specifically a methylated tetralol or methylated naphthol. Step 4 - Product identification: The major product corresponds to option (c): a bicyclic compound with an aromatic ring bearing a methyl substituent and a hydroxyl group on the saturated ring. This is consistent with 2-methyl-5,6,7,8-tetrahydro-2-naphthol type structure - the octalone aromatizes ring A under acidic conditions to give a phenol, with the methyl at C8a ending up as a ring substituent, and the resulting compound matches structure (c). Step 5 - Why other options fail: - Option (a): A monocyclic benzyl alcohol - the ring system cannot open under these mild acidic conditions. - Option (b): Shows a fully saturated bicyclic alcohol without aromatization, which is not favored; the thermodynamic driving force pushes toward the aromatic phenol. - Option (d): A fully saturated decalin with two methyls - no aromatization or hydroxyl, inconsistent with the enone starting material under acidic conditions. Therefore, the correct answer is C.