Synthesis Problems Answers | Chemsheets Organic

Question: Synthesize 4-nitrotoluene from benzene.

Analysis: Benzene (C₆H₆) → Methylbenzene (toluene) → 4-nitrotoluene. The nitro group (–NO₂) must be para to the methyl group.

Key Concept: Order of reactions matters. The methyl group is a 2,4-directing (activating) group. The nitro group is a 3-directing (deactivating) group. If you nitrate first, you get nitrobenzene. Then Friedel-Crafts alkylation fails because nitrobenzene is too deactivated. So you must alkylate first. Chemsheets Organic Synthesis Problems Answers

Answer:

Final Answer Sequence:

Based on analyzing hundreds of student attempts at Chemsheets problems, here are the top 5 errors:

| Mistake | Why It’s Wrong | Correct Fix | | :--- | :--- | :--- | | 1. Using HBr/peroxides on an internal alkene | Anti-Markovnikov only works on terminal alkenes; internal gives mixtures. | Use a different route (e.g., hydroboration-oxidation). | | 2. Trying to oxidize a tertiary alcohol | Tertiary alcohols don’t oxidize (no H on the C-OH). | You cannot make a ketone from a tertiary alcohol without breaking the C-C bond. | | 3. Using NaBH₄ to reduce a carboxylic acid | NaBH₄ is not strong enough; it leaves -COOH unchanged. | Use LiAlH₄ (in dry ether), then acid work-up. | | 4. Forgetting to quench a Grignard | Grignard reagents decompose in water/acid before reacting. | All reactions must be under anhydrous conditions; acid work-up is after the addition. | | 5. No heat or reflux stated | Many reactions (esterification, hydrolysis) require heating. | Always add “heat under reflux” unless it’s a room temperature reaction. | Question: Synthesize 4-nitrotoluene from benzene

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Work backward from the target molecule.
Example: Target = pentan-2-ol.
Backward: pentan-2-ol comes from pentan-2-one (reduction with NaBH4). Pentan-2-one comes from butanenitrile + CH3MgBr (Grignard). Butanenitrile from 1-bromopropane + KCN. Start from propane. Step 2: Nitration – Add the nitro group