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Friedel-Crafts reactions are among the most tested EAS topics. FC Alkylation drawbacks: (1) carbocation rearrangement (1° → 2° or 3° via 1,2-shifts), (2) polyalkylation (product more activated than starting material), (3) no reaction with deactivated rings or -NH2. FC Acylation advantages: (1) no rearrangement (resonance-stabilized acylium ion), (2) mono-substitution only (product is deactivated by -COR), (3) predictable regioselectivity. Synthetic strategy for installing an n-alkyl group without rearrangement: FC acylation → Clemmensen (acidic) or Wolff-Kishner (basic) reduction. Example: benzene → propiophenone → n-propylbenzene (Zn-Hg/HCl). To use FC on aniline: first protect as acetanilide (CH3COCl), perform FC reaction, then hydrolyze the amide. FC does not work on: nitrobenzene, cyanobenzene, benzoic acid, benzaldehyde, sulfonated benzene, or any strongly deactivated ring. For monohalogenation of highly activated rings (phenol, aniline): no Lewis acid needed — Br2/H2O suffices.