The mechanism behind electrophilic substitution reactions in aromatic compounds involves the interaction of an electrophile with the electron-rich aromatic ring, leading to the substitution of a hydrogen atom on the ring with the electrophile. This process occurs in several steps:1. Formation of the electrophile: In most cases, the electrophile is generated in the presence of a catalyst or a suitable reagent.2. Attack of the electrophile on the aromatic ring: The electrophile attacks the electron-rich aromatic ring, forming a positively charged intermediate called an arenium ion or a sigma complex. This step is the slow, rate-determining step of the reaction.3. Deprotonation of the intermediate: A base present in the reaction mixture removes a proton from the intermediate, restoring the aromaticity of the ring and generating the final substituted product.An example of an electrophilic substitution reaction is the nitration of benzene. In this reaction, benzene reacts with a mixture of concentrated nitric acid HNO3 and concentrated sulfuric acid H2SO4 to form nitrobenzene. The mechanism proceeds as follows:1. Formation of the electrophile: The nitronium ion NO2+ is generated by the reaction of nitric acid with sulfuric acid.HNO3 + H2SO4 NO2+ + HSO4- + H2O2. Attack of the electrophile on the aromatic ring: The nitronium ion NO2+ attacks the benzene ring, forming a sigma complex.Benzene + NO2+ Sigma complex C6H5NO2+ 3. Deprotonation of the intermediate: The HSO4- ion acts as a base and removes a proton from the sigma complex, restoring the aromaticity of the ring and generating nitrobenzene.Sigma complex C6H5NO2+ + HSO4- Nitrobenzene + H2SO4Electrophilic substitution reactions occur in aromatic compounds because the aromatic ring is electron-rich due to the delocalization of electrons. This electron-rich nature makes the ring susceptible to attack by electrophiles, leading to the substitution of a hydrogen atom with the electrophile. The aromaticity of the ring is temporarily lost during the reaction but is restored in the final step, ensuring the stability of the product.