Chemistry Reference
In-Depth Information
4.32
ortho
δ
-
CHO
C
3
δ
+
CHO
C
CHO
C
3
3
H
H
H
+
Cl
Cl
Cl
+
+
meta
CHO
C
CHO
C
CHO
C
3
3
3
+
+
H
H
H
+
Cl
Cl
Cl
para
δ
-
CHO
C
3
δ
+
CHO
C
CHO
C
3
3
+
+
+
H Cl
H Cl
H Cl
The carbonyl carbon in the acetophenone carries a partial positive charge because
oxygen is more electronegative than carbon. This partial charge is illustrated in the
first contributor to the intermediates for
ortho
or
para
substitution. Note that positive
charges appear on adjacent atoms in these contributors - an unfavorable situation.
No such contributor appears in the intermediate for
meta
substitution. Thus
meta
substitution predominates.
4.33
The major product is isopropylbenzene. Protonation of propene gives the 2-propyl
cation, a secondary carbocation, rather than the less stable 1-propyl cation, a
primary carbocation.
H
3
C
CH
3
CH
2
CH
2
CH
3
isopropylbenzene
propylbenzene
4.34
If the halides were not identical, the following kind of exchange could occur (see
eq. 4.13):
