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Benzene undergoes electrophilic aromatic substitution (EAS) rather than addition to preserve its aromatic stabilization energy (~150 kJ/mol). The three-step mechanism: (1) electrophile generation, (2) sigma complex $\frac{Wheland intermediate}{arenium ion}$ formation — the rate-determining step, (3) proton elimination to restore aromaticity. Named EAS reactions include halogenation $\frac{X2}{FeX3}$, nitration (HNO3/H2SO4 → NO2+), sulfonation $\frac{SO3}{H2SO4}$, Friedel-Crafts alkylation (RCl/AlCl3 → R+), and acylation (RCOCl/AlCl3 → RCO+). Directing effects are controlled by substituent electronic effects: activating groups with +M or +I donate electron density preferentially to ortho/para positions (-OH, -NH2, -OR, -R), making the sigma complex there more stable. Halogens are unique — deactivating (-I > +M overall) but still o/p directing (+M controls regiochemistry). Meta directors (-NO2, -CN, -COR) withdraw electrons, destabilizing the sigma complex especially at ortho/para where positive charge would sit directly on the substituted carbon. When two groups conflict, the stronger activator wins. FC limitations: no reaction on strongly deactivated rings, no reaction with -NH2 (complexes with Lewis acid), polyalkylation problem (acylation avoids this), and carbocation rearrangement in alkylation (solved by acylation → reduction). Sulfonation is the only easily reversible EAS — useful as blocking group strategy. The Clemmensen and Wolff-Kishner reductions convert FC acylation products to alkyl groups, providing a rearrangement-free alternative to direct alkylation.