Strong electron withdrawing groups prevents Friedel Crafts reaction because when a withdrawing group attracts the electrons decrease the availability of the electronic pair and the enough electronic density of it in order to make possible the aromatic electrophilic substitution.
Strong electron donating groups like NH2 doesn’t undergo Friedel Crafts reaction because NH2 is a Lewis base that means an electron donor. Due to Friedel Crafts reaction is an acid base reaction, the AlCl3 will be attacked by the lone pair available from NH2 producing a salt. The same occurs with phenol because the lone pair of electrons available in the OH group so Friedels Crafts doesn’t undergo with benzene attached to the strong electron donating groups NH2 or OH.
Strong electron withdrawing groups prevents Friedel Crafts reaction because the group attracts the electrons thereby leading to a decrease the availability of the electronic pair.
These are the set of reactions which are involved in the attachment of substituents to an aromatic ring.
The decrease in the availability of the electron pair decreases the possibility of an aromatic electrophilic substitution.
Strong electron donating groups like NH₂ doesn’t undergo Friedel Crafts reaction because NH₂ is a Lewis base and an electron donor which will lead to the reaction with AlCl₃ to produce a salt.
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