The reactivity of aromatic compounds towards electrophilic substitution reactions is significantly affected by the presence and nature of functional groups attached to the aromatic ring. Functional groups can be classified as either electron-donating groups EDGs or electron-withdrawing groups EWGs based on their inductive or resonance effects on the aromatic ring.Electron-donating groups EDGs increase the electron density of the aromatic ring, making it more nucleophilic and more reactive towards electrophilic substitution reactions. These groups generally direct the incoming electrophile to the ortho and para positions relative to the EDG. Examples of EDGs include -OH, -OCH3, -NH2, and alkyl groups.Electron-withdrawing groups EWGs decrease the electron density of the aromatic ring, making it less nucleophilic and less reactive towards electrophilic substitution reactions. These groups generally direct the incoming electrophile to the meta position relative to the EWG. Examples of EWGs include -NO2, -COOH, -CN, and -SO3H.Let's consider a specific example: the nitration of toluene methylbenzene compared to the nitration of nitrobenzene.Toluene has a methyl group -CH3 attached to the aromatic ring, which is an electron-donating group. This increases the electron density of the ring, making it more reactive towards electrophilic substitution reactions. In the nitration reaction, the electrophile is the nitronium ion NO2+ , which is generated from the reaction of concentrated nitric acid HNO3 and concentrated sulfuric acid H2SO4 .Mechanism for nitration of toluene:1. The electrophile, NO2+, attacks the electron-rich aromatic ring, forming a sigma complex arenium ion with the positive charge localized on the ortho and para carbons relative to the methyl group.2. A proton is lost from the arenium ion, and the aromaticity is restored, resulting in the formation of ortho-nitrotoluene and para-nitrotoluene as major products.On the other hand, nitrobenzene has a nitro group -NO2 attached to the aromatic ring, which is an electron-withdrawing group. This decreases the electron density of the ring, making it less reactive towards electrophilic substitution reactions. The nitration of nitrobenzene will be slower than the nitration of toluene due to the presence of the electron-withdrawing nitro group.In summary, the substitution of different functional groups on aromatic compounds significantly affects their reactivity towards electrophilic substitution reactions. Electron-donating groups increase the reactivity, while electron-withdrawing groups decrease the reactivity. Additionally, these functional groups also influence the regioselectivity of the reaction, directing the electrophile to specific positions on the aromatic ring.