Chemistry Reference
In-Depth Information
13.8
+
+H
+
H
Br
O
O
O
Br
Br
Br
H
H
+
+
O
Br
O
Br
ADDITIONAL PROBLEMS
13.9
Three minor dipolar contributors are:
4
+
2
6
+
+
N
N
-
N
-
-
These structures suggest that the carbons in pyridine are partially positively charged
(due to the electron-withdrawing effect of the nitrogen) and, therefore, are expected
to be deactivated (relative to benzene) toward reaction with electrophiles. Note that
the positive charge is distributed between carbons 2, 4, and 6. Therefore, these
carbons should be less reactive toward electrophiles than carbon 3 (or 5).
13.10
HNO
3
N
O
2
H
2
S
O
4
H
3
C
C
H
3
H
3
C
C
H
3
N
N
The methyl groups are electron-donating and activate aromatic compounds toward
electrophilic aromatic substitution (see Secs. 4.10 and 4.11). Therefore,
2,6-dimethylpyridine undergoes nitration under much milder conditions than required
by pyridine. Notice that nitration occurs
ortho
and
para
to the methyl groups.
13.11
Compare with eq. 13.3 and Example 13.2.
+
+
LiH
N
N
Li
