See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the substrate: alpha-tetralone is a bicyclic compound consisting of a benzene ring fused to a cyclohexanone ring. The carbonyl (C=O) is at position 1, and the aromatic ring carbons are at positions 5, 6, 7, 8, 4a, and 8a. Step 2 - Determine directing effects: The carbonyl group attached at C8a (the ring fusion carbon adjacent to the aromatic ring) acts as a meta-director and deactivator for electrophilic aromatic substitution. The other ring fusion carbon C4a is connected to the aliphatic CH2 chain and acts essentially as an alkyl substituent, which is an ortho/para director. Step 3 - Predict the position of sulfonation: The aromatic ring has two substituents influencing EAS: (i) the carbonyl at C8a (meta-director) directs to C6 and C5 (meta positions relative to C8a), and (ii) the alkyl-like C4a junction (ortho/para director) directs to C6, C8, and C5 (ortho and para to C4a). The position C6 is both meta to C8a AND ortho to C4a, making it doubly activated and the most favorable position for electrophilic attack. Step 4 - Assign the correct product: Sulfonation at C6 gives the product shown in option (b), where the HO3S group is at the 6-position of the aromatic ring (ortho to the C4a ring junction and meta to the C8a carbonyl-bearing ring junction). Step 5 - Eliminate other options: Option (a) places SO3H at C8 (ortho to C8a carbonyl = deactivated position, ortho to C4a = activated, but ortho to the electron-withdrawing carbonyl carbon makes this less favored than C6). Option (c) places SO3H at C6 but the structural drawing corresponds to a different regiochemistry. Option (d) places SO3H at C5 (peri position adjacent to CH2, sterically hindered and not the most activated position). Therefore, the correct answer is B.