Final answer:
In electrophilic aromatic substitution reactions, the limiting reagent is often the electrophile, as it needs to be strong enough to react with the aromatic ring of benzene. The reaction involves an intermediate where the ring eliminates a proton after being attacked by the electrophile.
Step-by-step explanation:
The limiting reagent in an electrophilic aromatic substitution reaction is the reactant that is completely consumed first and therefore determines the maximum amount of product that can be formed. While the characteristics of benzene make it a nucleophile, its relatively weak nucleophilic character means that it requires a strong electrophile to react. Thus, in the context of electrophilic aromatic substitution, the electrophile is often the limiting reagent due to its requirement to be strong enough to overcome the energy barrier associated with disrupting the aromatic stability of benzene.
Typical reactions include the halogenation of benzene, where a halogen such as chlorine (Cl2) is used in the presence of a Lewis acid catalyst like FeCl3 to substitute a hydrogen atom on the benzene ring. The process forms a very unstable intermediate, after which the ring eliminates a proton, forming the halogenated product and regaining aromatic stability. The reaction mechanism typically involves a step where the electrophile is generated, followed by its attack on the aromatic ring, and then deprotonation to restore aromaticity.