Electrophilic Aromatic Substitution
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General reaction of EAS
Ar-H + EA = Ar-E + H-A ; Ar-H arenes EA -electrophile
Benzene + X2,FeX3= ? Halogenation reaction
Benzene + X2,FeX3= benzene-X + HX
Benzene + HONO2/H2SO4 = ? ( Nitration Reaction )
Benzene + HONO2/H2SO4 = Benzene-NO2 + H20
Benzene + SO3/H2SO4= ? ( Sulphonation Reaction )
Benzene + SO3/H2SO4= benzene-SO3H
Benzene + RCl/AlCl3= ? (Friedel Craft Alkylation)
Benzene + RCl/AlCl3= benzene-R + HCl
Benzene + RCOCl/AlCl3= ? ( Fridel craft acylation )
Benzene + RCOCl/AlCl3= benzene-RCO + HCl
True intermediate in EAS reaction ?
Arenium ion
Facts about Activating groups( op directors )
Fast reactions take place. Direct incoming electrophile towards ortho or para position. Occurrence mostly due to resonance effect. Low Activation barrier and stabler Arenium ion.
Facts about deactivating groups ( m directors )
Slow reactions take place. Direct incoming electrophile towards meta position. Have partial or full positive charge on atom directly attached to ring Higher Activation barrier and less stabler Arenium ion.
Electron Releasing group effect on transition state, Activation barrier and reaction rate.
Make transition state stabler. Lower Activation barrier. High reaction rate.
Electron withdrawing group effect on transition state , Activation barrier and reaction rate.
Make transition state stabler. Increases activation barrier. Slower reaction rate.
? Groups cause the group to be more stabler than benzene itself in EAS ?
Activating groups.
Op directors list.
-NH2, -OH, O- , NHCOCH3 , OCH3, OR, CH3( R ) , C6H5 , -F/Cl/Br/I( weakly deactivating )
Mera directors list.
-C=- N, SO3H, CO2H, CO2R, CHO, NO2 , CF3, CCl3