The reaction involving the substitution of an alkyl group on a benzene ring by the replacement of a hydrogen atom is named the Friedel-Crafts reaction.

Alkyl halides in combination with a Lewis acid catalyst are used in Friedel-Crafts alkylation reactions.

Only the alkyl halides in which the halogen atom is bonded to a\({\bf{s}}{{\bf{p}}^{\bf{3}}}\)hybridized carbon undergo Friedel-Crafts alkylation reactions.

Carbon atoms bonded to four other atoms/groups are said to be \(s{p^3}\) hybridized.

Here, the halide group is attached to an \(s{p^2}\) hybridized carbon atom and is therefore unreactive towards Friedel-Crafts alkylation reaction.

Here, the halide group is attached to an \(s{p^3}\) hybridized carbon atom and is therefore reactive towards Friedel-Crafts alkylation reaction.

Here, the halide group is attached to an \(s{p^2}\) hybridized carbon atom and is therefore unreactive towards Friedel-Crafts alkylation reaction.

Here, the halide group is attached to an \(s{p^3}\) hybridized carbon atom and is therefore reactive towards Friedel-Crafts alkylation reaction.