Benzene as an Electrophile:
Nucleophilic Aromatic Substitution
H
Cl
NO2
O
NO2
NaOH
H2O, 100 ˚C
NO2
NO2
addition / elimination
This reaction goes by an ___________________
pathway,
analogous to nucleophilic acyl substitution (recall that substitution
reactions at sp2 carbon do not follow the [SN2] pathway).
Mechanism of Nucleophilic
Aromatic Substitution
Cl
NO2
Cl OH O
N
OH
[AdN]
addition step
(slow step)
NO2
H
O
N
O
Cl OH O
N
Cl
O
NO2
O
O
N
O
N
Cl OH O
N
O
O
N
O
O
[Eβ]
elimination step
(fast step)
NO2
O
Cl OH O
N
O
O
Substrate Requirements for
Nucleophilic Aromatic Substitution
Cl
NO2
•  EWG to activate ring (lower LUMO energy)
•  Good leaving group (–F best in these reactions)
NO2
ortho or _____
The EWG must be located ______
para positions.
A variety of nucleophiles can be used. The incoming
group must be a stronger base than the outgoing
leaving group.