See image — Alcohols Phenols and Ethers Chemistry Question

💡 Solution & Explanation

Concept: Acid-catalyzed dehydration of tertiary alcohols proceeds via E1 mechanism through a carbocation intermediate, with Zaitsev/most stable alkene as major product, and aromatic stabilization can drive ring formation or conjugation. Step 1 - Identify the starting material: The starting material is a tertiary benzylic alcohol where the OH-bearing carbon is at the ring junction of a partially saturated naphthalene system (8a position of an octahydronaphthalene), bearing an ethyl group. Specifically, it is 8a-ethyl-3,4,4a,5,6,7,8,8a-octahydronaphthalen-8a-ol or equivalently a compound where a quaternary carbon bears OH, ethyl, is part of a cyclohexane ring, and is bonded to the ortho carbon of a benzene ring — making the carbon both tertiary and benzylic. Step 2 - Protonation and carbocation formation: H2SO4 protonates the OH, water leaves to give a tertiary carbocation at the ring junction carbon. This carbocation is stabilized by the adjacent benzene ring (benzylic stabilization). Step 3 - Elimination pathways: The carbocation can lose a proton from the adjacent cyclohexane ring carbons (C8 or C4a positions) to form an alkene. Elimination toward the ring junction gives a double bond that is conjugated with the benzene ring (endocyclic, forming a dihydronaphthalene/1,2-dihydronaphthalene type), which is more stable than an exocyclic alkene. Alternatively, loss of a proton from the ethyl group gives an exocyclic alkene. Step 4 - Most stable product: Loss of a proton from the cyclohexane ring adjacent carbon forms a trisubstituted endocyclic double bond conjugated with the aromatic ring, giving 1-ethyl-3,4-dihydronaphthalene or upon further consideration, the most stable product is 1-ethyl-1,2,3,4-tetrahydronaphthalene ... but actually the elimination gives a double bond in the ring. The product (a) shows 1-ethyl-3,4-dihydronaphthalene (one aromatic ring fused with a ring containing one double bond) with ethyl at C1 — this is the product of endocyclic elimination giving a vinylogous/conjugated system. Step 5 - Why other options fail: (b) requires loss of the ethyl group or extensive rearrangement to give a naphthalene with propyl — unlikely. (c) shows an exocyclic double bond (ethylidene substituent) which is less stable than the endocyclic conjugated alkene. (d) shows a spiro or non-fused product inconsistent with the starting material connectivity. Step 6 - Conclusion: The major product is option (a), 1-ethyl-3,4-dihydronaphthalene (or 1-ethyl-1,2-dihydronaphthalene), formed by endocyclic elimination giving maximum conjugation with the benzene ring. Therefore, the correct answer is A.