Sigma Complex
Intermediate
is more
stable if
nitration
occurs at
the ortho
or para
position.
=>
Energy Diagram
=>
Activating, O-, PDirecting Substituents
Alkyl groups stabilize the sigma complex by
induction, donating electron density
through the sigma bond.
Substituents with a lone pair of electrons
stabilize the sigma complex by resonance.
OCH3
+
OCH3
NO2
NO2
+
H
H
=>
Nitration of Anisole
Ortho attack
Meta attack
Para attack
=>
The Amino Group
Aniline reacts with bromine water (without a
catalyst) to yield the tribromide. Sodium
bicarbonate is added to neutralize the
HBr that’s also formed.
NH2
NH2
Br
Br
3 Br2
H2O, NaHCO3
Br
=>
Summary of
Activators
=>
Deactivating MetaDirecting Substituents
Electrophilic substitution reactions for
nitrobenzene are 100,000 times slower
than for benzene.
The product mix contains mostly the meta
isomer, only small amounts of the ortho
and para isomers.
Meta-directors deactivate all positions on
the ring, but the meta position is less
deactivated.
=>
Ortho Substitution
on Nitrobenzene
=>
Para Substitution
on Nitrobenzene
=>
Meta Substitution
on Nitrobenzene
=>