See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Aromatic compounds undergo reactions that preserve the aromatic ring's stability. The mechanism involves an electrophile attacking the electron-rich aromatic ring. Step 1: Identify the substrate. The starting material is phenol (a benzene ring with an -OH group), which is an aromatic compound. Aromatic rings are electron-rich systems. Step 2: Identify the reagent. Br2 acts as an electrophile. In the presence of the electron-donating -OH group on the ring, Br2 is polarized and acts as an electrophile attacking the aromatic pi system. Step 3: Identify the reaction type. The reaction involves the aromatic ring acting as a nucleophile attacking the electrophilic Br2. Three H atoms on the ring (at ortho and para positions relative to OH) are replaced by Br atoms, and 3HBr is produced. This is a substitution reaction (H is replaced by Br) at an aromatic ring, driven by an electrophile. Step 4: Confirm it is electrophilic substitution. The aromatic ring donates electrons to the incoming electrophile (Br+), forming a sigma complex (arenium ion), and then loses a proton to restore aromaticity. This is the classic electrophilic aromatic substitution (EAS) mechanism. Why other options fail: - (a) Nucleophilic addition: Addition would destroy aromaticity; also the ring is not acting as a nucleophile in an addition sense here. - (b) Nucleophilic substitution: The ring does not act as a substrate for a nucleophile; Br2 is the electrophile, not a nucleophile. - (c) Electrophilic addition: Addition would destroy aromaticity, and the product would not be aromatic; no HBr would be lost. - (e) Free radical substitution: No radical initiator or conditions are mentioned; the -OH group activates the ring toward electrophiles, not radicals. Therefore, the correct answer is D.