Isomeric hydrocarbons negative Baeyer's test (Molecular formula C9H12) The total number of isomers f — JEE Mains Chemistry Past Papers Chemistry Question

💡 Solution & Explanation

# Solution: C₉H₁₂ Isomers Failing Baeyer's Test **Step 1: Interpret the conditions** - Molecular formula: C₉H₁₂ - Negative Baeyer's test means NO C=C double bonds or rings - Must be saturated hydrocarbons (alkanes only) - Need exactly 4 different non-aliphatic (aromatic) substitution sites **Step 2: Identify the core structure** - C₉H₁₂ with only aromatic rings and single bonds - This indicates a benzene ring (C₆H₄) as the base with C₃H₈ as substituents - The compound must be **trimethylbenzene (xylene derivatives with one additional methyl)** **Step 3: Determine substitution pattern** - For "four different non-aliphatic substitution sites," we need 4 positions on the benzene ring to be distinct - This requires the substituent pattern to create 4 magnetically/chemically different aromatic positions **Step 4: Count isomers with 4 different aromatic positions** - 1,2,3-trimethylbenzene has 4 different aromatic hydrogen positions ✓ - 1,2,4-trimethylbenzene has 4 different aromatic hydrogen positions ✓ - 1,3,5-trimethylbenzene has only 2 different positions (symmetric) ✗ - 1,2,3,4-tetramethylbenzene (C₁₀H₁₄) - wrong formula **Step 5: Identify valid isomers** Only **1,2,3-trimethylbenzene** and **1,2,4-trimethylbenzene** have exactly four different non-aliphatic substitution sites. **Therefore, the answer is 2**