See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 – Reaction of benzene with cyclohexene under H2SO4/heat (Friedel-Crafts alkylation): Cyclohexene is protonated by H2SO4 to give a cyclohexyl carbocation (or allylic carbocation via hydride shift). Electrophilic aromatic substitution of benzene gives 1-phenylcyclohexene (A). The double bond remains in the ring adjacent to the phenyl-bearing carbon, giving 1-phenylcyclohex-1-ene (or the most stable alkylbenzene with the double bond conjugated/adjacent to the ring). Actually, under acidic conditions, benzene undergoes Friedel-Crafts with the cyclohexyl cation, but since cyclohexene can form a tertiary-like allylic cation, the product A is 1-phenylcyclohexene (cyclohexene with phenyl at C1, i.e., the double bond at C1-C2). Step 2 – NBS followed by alc. KOH: NBS performs allylic bromination of 1-phenylcyclohexene. The allylic position adjacent to the double bond is brominated. Alcoholic KOH then causes dehydrohalogenation (E2 elimination), generating a new double bond. Starting from 1-phenylcyclohexene (double bond C1=C2), allylic bromination occurs at C3 (allylic to C2), giving 3-bromo-1-phenylcyclohex-1-ene. Alcoholic KOH eliminates HBr to give 1-phenylcyclohex-1,3-diene or shifts the double bond. More precisely, elimination from C3-Br with the adjacent C2-H gives the conjugated diene, or elimination toward C4 gives 1-phenylcyclohex-2-ene (shifting double bond). The net result of NBS/alc.KOH on 1-phenylcyclohexene is to give 3-phenylcyclohexene (double bond shifted) or 1-phenylcyclohex-2-ene. The key product B is 1-phenylcyclohex-2-ene, which has the double bond at C2-C3 and phenyl at C1. This corresponds to option (b) description: a cyclohexene ring with Ph at C1 and a double bond, ready for epoxidation. Step 3 – RCO3H (peracid) epoxidation: A peracid converts the double bond in B to an epoxide via syn addition (concerted mechanism), giving the corresponding epoxide C. The double bond in 1-phenylcyclohex-2-ene (B) is epoxidized to give 1-phenyl-2,3-epoxycyclohexane. This matches option (b): a cyclohexane ring bearing a Ph group at C1 and an epoxide at C2-C3. Why other options fail: - Option (a): Shows an epoxide with Ph at C4, not consistent with the reaction sequence. - Option (c): Shows a diol; a peracid gives an epoxide, not a diol directly. - Option (d): Shows a fused benzene-cyclohexane epoxide (tetralin epoxide), which would require intramolecular cyclization not described here. Therefore, the correct answer is B.