Benzene is a unique aromatic compound that undergoes a specific type of reaction known as electrophilic aromatic substitution (EAS). This mechanism is crucial because it allows benzene to react without losing its aromaticity, which is a key factor in its stability. Aromaticity can be tested through four criteria, and if any of these are violated, the compound becomes less stable.

One common reaction that might come to mind is halogenation, where a diatomic halogen adds across a double bond, typically resulting in a dihalide. However, with benzene's three double bonds, one might assume that halogenation could occur three times. This is not the case, as such a reaction would lead to a non-aromatic product, breaking the rules of aromaticity and resulting in a less stable compound due to the loss of full conjugation.

To maintain aromaticity, benzene must undergo substitution rather than addition. In a substitution reaction, one of the hydrogen atoms on the benzene ring is replaced by a reagent, allowing the compound to retain its aromatic structure. This is where strong electrophiles, denoted as E⁺, come into play. These electron-loving species can temporarily disrupt the aromatic system to facilitate the substitution, but the system will revert to its aromatic state by the end of the reaction.

The general mechanism of EAS involves the formation of a sigma complex, where the electrophile attacks the benzene ring, leading to the temporary loss of aromaticity. Subsequently, a proton is removed, restoring the aromatic character of the compound. This process is essential for understanding how benzene and its derivatives can be transformed while preserving their stability and unique properties.