In the general mechanism of Electrophilic Aromatic Substitution (EAS), why is the formation of the arenium ion (sigma complex) highly endothermic and considered the rate-determining step?

Question

Prashant Kotian · Accepted Answer

Correct answer: B. In step 1, the electrophile bonds to a carbon, changing its hybridization to sp3. This breaks the cyclic conjugation, costing the molecule its 36 kcal/mol resonance energy, creating a massive activation barrier.

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