Practice Problems

Chapter 7 Practice Problems

Chapter 7 Practice Problems

Work these before checking references or notes.

  1. Directing groups and rate ranking: For each monosubstituted benzene, state whether a new electrophile will add ortho, meta, or para. Then rank them (1 = fastest, 5 = slowest) for nitration:
    a) Nitrobenzene (C₆H₅–NO₂)
    b) Phenol (C₆H₅–OH)
    c) Toluene (C₆H₅–CH₃)
    d) Benzene (C₆H₆)
    e) Bromobenzene (C₆H₅–Br)
    Hint: –NO₂ is meta/strongly deactivating; –OH is o/p/strongly activating; –CH₃ is o/p/activating; halogens are o/p but deactivating.

  2. Predict the major products (orientation and major isomer):
    a) Nitration of chlorobenzene (Cl, FeBr₃ not needed; use HNO₃/H₂SO₄).
    b) Bromination of anisole (C₆H₅–OCH₃) with Br₂/FeBr₃.
    c) Sulfonation of nitrobenzene with fuming H₂SO₄.
    d) Friedel–Crafts acylation of toluene with acetyl chloride/AlCl₃.
    e) Nitration of p-xylene (1,4-dimethylbenzene).

  3. Synthesis planning: Outline a route from readily available aromatics to 3-bromobenzoic acid. Consider directing effects to place Br meta to COOH. Hint: One path is: toluene → oxidize to benzoic acid → nitration (meta) → reduction to amine → diazotization → Sandmeyer bromination.

  4. Resonance and stability: Using sigma-complex resonance forms, explain why –NO₂ directs meta and deactivates. What happens in the ortho/para sigma complexes that makes them especially unstable?

  5. Controlling polysubstitution: Direct nitration of phenol gives mostly ortho-nitrophenol (plus some para). Propose a strategy to favor p-nitrophenol. Hint: Either protect –OH as an acyl group (less activating, bulkier) before nitration, then deprotect; or temporarily sulfonate to block ortho, nitrate para, then desulfonate.