See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Electrophilic aromatic substitution (Friedel-Crafts type alkylation) via protonation of an alkene by a strong acid to generate a carbocation, which then acts as an electrophile toward benzene. Step 1 – Protonation of cyclohexene: Concentrated H2SO4 protonates the double bond of cyclohexene according to Markovnikov's rule, generating the cyclohexyl carbocation (a secondary carbocation at C1 of the cyclohexane ring). Step 2 – Electrophilic attack on benzene: The cyclohexyl carbocation is a good electrophile. It attacks the π-system of benzene (electrophilic aromatic substitution). The arenium ion (sigma complex) intermediate then loses a proton to regenerate the aromatic ring. Step 3 – Product: The result is cyclohexylbenzene — a benzene ring bearing a cyclohexyl substituent. This is the sole major organic product after the acid is washed away and excess benzene is removed. Why other options fail: (b) 1-cyclohexylcyclohexene would require cyclohexene acting as the nucleophile toward the carbocation (rather than benzene), but benzene is present in large excess and is a much better nucleophile in this context; also, the reaction would generate another carbocation rather than a stable product without further steps. (c) trans-1,2-diphenylcyclohexane would require two phenyl groups adding across the double bond, which is not the mechanism here. (d) 1,1-diphenylcyclohexane would require two benzene rings adding to the same carbon, inconsistent with the straightforward monoalkylation occurring under these mild (0°C) conditions. Therefore, the correct answer is A.