Friedel- Crafts reaction: When any benzene or its derivative is treated with alkyl halide (R-X, X=Cl) or acetyl chloride (CH₃-COCl) in the presence of annhydrous aluminium chloride (AlCl₃) to form alkyl or acetyl substituted benzene or its derivative, this reaction is called Friedel-Crafts reaction.

⇒ Friedel-Crafts alkylation: When any benzene or its derivative is treated with alkyl halides (R-X, X=Cl,Br) in the presence of annhydrous aluminium chloride (AlCl₃) to form alkyl substituted benzene or its derivatives, this reaction is called Friedel-Crafts alkylation. For example:

⇒ Friedel-Crafts acylation: When any benzene or its derivative is treated with acetyl chloride (R-COCl) in the presence of annhydrous aluminium chloride (AlCl₃) to form acetyl substituted benzene or its derivatives, this reaction is called Friedel-Crafts acylation. For example:

Aniline does not undergo Friedel-Crafts reaction.

Explanation: Aniline is a Lewis base (electron-pair acceptor) while AlCl₃ is Lewis acid (electron-pair donor). They combine with each to form a salt.

Due to presence of positive charge on nitrogen (N) atom in the salt, the group N⁺H₂AlCl₃^- acts as a strong electron withdrawing group (strong deactivating group). As a result, it reduces the electron density in the benzene ring and hence aniline does not undergo Friedel-Crafts (alkylation or acetylation) reaction