See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the starting material: The starting material is an ortho-substituted benzene bearing a -CHCl-CHCl2 side chain (a benzene with a 1,2-dichloroethyl group where the benzylic carbon carries one Cl and the terminal carbon carries two Cl atoms, i.e., PhCHCl-CHCl2 arrangement at ortho positions - actually examining the structure more carefully, the compound is a benzene ring with at one position -CHCl- and at the adjacent position -CHCl2, making it an ortho bis(chloromethyl) type: one carbon has one Cl (benzylic CHCl) and another has two Cl (CHCl2)). Step 2 - Reaction with HO- (base): HO- acts as a base/nucleophile. With 4 moles of HO- reacting with 2 moles of substrate, that is 2 equivalents of HO- per molecule of substrate. Step 3 - Mechanism: The CHCl2 group undergoes elimination or substitution. With HO-, the CHCl2 group loses HCl to form a -CHCl- (via E2 or substitution), or the CHCl groups undergo intramolecular reaction. More precisely, HO- can deprotonate or substitute on the CHCl2 to give -CHCl-O- (after loss of Cl-). The benzylic CHCl can also react with HO- to give -CH(OH)- or form an alkoxide. The key reaction: each CHCl2 group reacts with one OH- to displace one Cl- giving -CHClOH → -CHClO- (alkoxide), which then undergoes intramolecular cyclization. Step 4 - Product formation: Two molecules of the ortho-dihalide substrate react with 4 OH- (2 per molecule). Each molecule loses 2 HCl equivalents. The two benzylic CHCl groups from two different molecules couple through two oxygen bridges: one oxygen comes from each OH- attacking the CHCl of one molecule while the alkoxide from the other molecule displaces the Cl of the first, forming a symmetric dibenzo-1,4-dioxane. This gives a structure where two benzene rings are connected by two -O-CHCl- bridges (the dioxane ring), with each bridging carbon retaining one Cl atom. Step 5 - Counting Cl in product: Each bridging carbon originally had CHCl (benzylic) or CHCl2 (terminal). After losing 2 Cl per molecule (one from each CHCl/CHCl2), 2 Cl remain per molecule, giving 4 Cl total in the dimer, symmetrically placed - two Cl on each side (one on each bridging carbon of the dioxane ring on each benzene unit), matching option (b) which shows 4 Cl atoms symmetrically on the bridging carbons with no methyl groups. Step 6 - Why other options fail: (a) has a methyl group which is not present in the starting material. (c) and (d) have incorrect substitution patterns or methyl groups inconsistent with the starting material. Option (b) correctly shows the symmetric 2,3-dichloro-2,3-dihydro-1,4-benzodioxin dimer with 4 Cl atoms on the bridging sp3 carbons. Therefore, the correct answer is B.