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298 Chapter 8
Copyright © 2017 Pearson Education, Inc.
103.
The electrophile can add to either end of the conjugated system. Adding the electrophile to one end forms
A
and
B
; adding the electrophile to the other end forms
C
and
B
.
a.
Br
2
Br
Br
A
CH
2
Br
+
CH
2
Br
+
B
C
Br
Br
b. A
has two asymmetric centers, but only two stereoisomers are obtained because only anti addition of
Br
2
can occur.
+
B
has four stereoisomers because it has an asymmetric center and a double bond that can be in either
the
E
or
Z
configuration.
+
+
+
C
has two stereoisomers because it has one asymmetric center.
CH
2
Br
+
H Br
CH
2
Br
Br
H