The substitution reactions of benzene with nitric and sulfuric acid involve the formation of nitrobenzene, which is an example of an electrophilic aromatic substitution EAS reaction. The mechanism behind this reaction can be broken down into several steps and is closely related to the reactivity of aromatic compounds.1. Formation of the electrophile: Nitric acid HNO3 reacts with sulfuric acid H2SO4 to form the nitronium ion NO2+ , which acts as the electrophile in this reaction. The reaction can be represented as follows:HNO3 + H2SO4 NO2+ + HSO4- + H2O2. Electrophilic attack on the benzene ring: The electrophile, NO2+, attacks the benzene ring, which is rich in electron density due to the presence of delocalized electrons. This attack results in the formation of a resonance-stabilized carbocation called the sigma complex or arenium ion. The aromaticity of the benzene ring is temporarily lost in this step.3. Deprotonation and regeneration of aromaticity: A base, usually the bisulfate ion HSO4- , abstracts a proton from the carbon atom where the nitro group is attached. This step restores the aromaticity of the benzene ring and forms nitrobenzene as the final product.The reactivity of aromatic compounds in electrophilic aromatic substitution reactions is influenced by the electron-donating or electron-withdrawing nature of substituents already present on the benzene ring. Electron-donating groups EDGs , such as -OH, -OCH3, and -NH2, increase the electron density of the ring, making it more susceptible to electrophilic attack. These groups generally direct the incoming electrophile to the ortho and para positions relative to themselves.On the other hand, electron-withdrawing groups EWGs , such as -NO2, -COOH, and -CN, decrease the electron density of the benzene ring, making it less reactive towards electrophilic attack. These groups direct the incoming electrophile to the meta position relative to themselves.In summary, the mechanism behind the substitution reactions of benzene with nitric and sulfuric acid involves the formation of an electrophile NO2+ , electrophilic attack on the benzene ring, and deprotonation to regenerate aromaticity. The reactivity of aromatic compounds in such reactions is influenced by the electron-donating or electron-withdrawing nature of substituents already present on the benzene ring.