Reactions of Aromatic Compounds

Mechanism of Nitration
(1) Generation of the Electrophile
Nitric acid undergoes reversible dehydration in the presence of
concentrated sulfuric acid producing the nitronium ion, a strong
electrophile.
H-O
: :
: O:
N
+
=
pK a = -1.4
+
H-O
H
:
O:
-
: :
: O:
N
+
=
O:
-
: :
+ H-OSO 3H
pK a = -9
H 2O +
+
H-O
H
:
: O:
N
:
O:
: O:
N
=
+
=
+
=
Nitronium ion
O:
-
: :
+ -OSO3H