Question

Account for the following:

Aniline does not undergo Friedel-Crafts reaction.

Answer 1

Aniline being a Lewis base reacts with Lewis acid AlCl₃ to form a salt.

\[\ce{C6H5\overset{\bullet\bullet}{N}H2 + AlCl3 -> C6H5\overset{+}{N}H2AlCl^-_3}\]

Due to the presence of a positive charge on N-atom in the salt, the group \[\ce{-\overset{+}{N}H2AlCl^-_3}\] acts as a strongly deactivating group. As a result, it reduces the electron density in the benzene ring and inhibits the electrophilic substitution reaction. Therefore, aniline does not undergo the Friedel-Crafts reaction.