Chemistry Reference
In-Depth Information
b.
HNO
3
CH
3
O
2
N
CH
3
O
O
c.
C
H
3
COCl
H
3
C
CH
3
CH
3
SnCl C
O
13.19
Examine the intermediates derived from electrophilic attack at each position.
4
O
O
H
H
E
E
+
+
N
H
H
+
+
-
E
attack at C-3
H
E
3
(Indole)
2
N
N
H
H
+
E
attack at C-2
+
+
-
H
E
E
H
N
N
H
H
Attack at C-3 gives a carbocation that is resonance-stabilized by a nonbonded pair of
electrons
on the adjacent nitrogen
. Attack at C-2 gives a cation in which the positive
charge is not adjacent to an atom bearing nonbonded electrons. Any additional
resonance contributors disrupt the benzenoid structure in the “left” ring. Therefore,
electrophilic aromatic substitution reactions of indole occur primarily at
C-3.
13.20
Imidazole is a good nucleophile and will react with primary alkyl halides, at one
nitrogen and then the other:
13.21
The nitrogen has a nonbonded electron-pair in an
sp
2
orbital at right angles to the
cyclic array of
p
orbitals. Therefore, it will be more basic than pyrrole.
