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SN-Ar-( NUCLEOPHILIC AROMATIC SUBSTITUTION:


SN2 (Aromatic) Type: Chloro benzene does not under goes Nucleophilic substitution reaction in ordinary condition due to following reason.

C–X bond in aryl halide is stable due to delocalisation of electrons by resonance. Also (C–X) bond possesses a double bond character like vinyl chloride and is stronger than C–X bond in alkyl halide.


Case-(1): Hence, SN reaction is not possible in benzene nucleus under ordinary conditions. However, under high temperature and pressure, SN reaction is made possible.
 Case-(2): However Nucleophilic substitutions occur in the presence of one or more electron withdrawing (EWG) at ortho and para position. These electron-withdrawing groups must be positioned ortho or para to the leaving group. The greater the number of electron-withdrawing substituents, the easier it will be to carry out the nucleophilic aromatic substitution reactions. 
EXAMPLE:

While electron releasing group (ERG) destabilizes carbanium ion and deactivated.
OTHER EXAMPLES:


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