See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Solution This reaction involves cleavage of an ether ($-OCH_3$) by hydrobromic acid. **Step 1: Identify the substrate** - Starting material: 4-methylanisole (para-cresyl methyl ether) - Contains both $-CH_3$ and $-OCH_3$ groups on the benzene ring **Step 2: Reactivity with HBr** - HBr cleaves ethers via the mechanism: $R-O-R' + HBr \rightarrow R-OH + R'-Br$ - The methoxy group ($-OCH_3$) is cleaved preferentially because it's an ether, not an alcohol - Breaking the $C-O$ bond of $-OCH_3$ gives methanol and a carbocation intermediate **Step 3: Carbocation formation & rearrangement** - Initial cleavage: $Ar-O-CH_3 + HBr \rightarrow Ar^+$ (aryl cation) $+ CH_3OH + Br^-$ - The aryl cation is unstable; **rearrangement occurs** where the $-CH_3$ group migrates to form a new C-C bond - This gives a new aromatic ring: $CH_3-\text{(benzene)}-CH_3$ (para-dimethylbenzene core structure that dimerizes) **Step 4: Final product** - The coupling product forms: $CH_3-\text{(benzene)}-O-\text{(benzene)}-CH_3$ - This is a diaryl ether with methyl groups on each ring **Why other options are wrong:** - **(A)** Only dealkylation without rearrangement - **(B)** Would require replacement of $-OCH_3$ with $-Br$, but Br attacks C, not the ether oxygen in this context - **(C)** ✓ Correctly shows the dimerization product from ether cleavage and rearrangement **Answer: (C)** — 4,4'-dimethoxybiphenyl or the equivalent coupled product from ether fragmentation and rearrangement.