Reactivity
Benzene is a nucleophile due to its π electrons, but its reactions are slow relative to those of alkenes with the same electrophile (Br2 for example). Thus reagents for the aromatic electrophilic substitutions shown below are a combination of the source of the electrophile and a catalyst which activates the electrophile.
| forming a benzene-carbon bond | forming a benzene-halogen bond | |||||
 | CH3COCl  AlCl3 |  | | Br2 FeBr3 |  | |
| CH3Cl AlCl3 |  | Cl2 FeCl3 |  | |||
| forming a benzene-nitrogen bond | forming a benzene-sulfur bond | |||||
| | conc HNO3 conc H2SO4 |  | | SO3 conc H2SO4 |  | |