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638 Chapter 18
Copyright © 2017 Pearson Education, Inc.
88.
a.
CH
3
O
O
O
H Cl
CH
3
O
O
O
H
+
CH
3
O
+
+
H HO
O
B
HO
O
H B
+
CH
3
O
O
H
H
2
O
B
CH
3
O
O
+ HB
+
HO
CH
3
O
CH
3
O
H
O
+
b.
NH
OH
+
N
OH
CH
2
+
N
OH
H
+
B
N
OH
HB
+
imine
formation
H H
C
O
89.
A fluoro substituent is more electronegative than a chloro substituent. Therefore, nucleophilic attack on the
carbon bearing the fluoro substituent is easier than nucleophilic attack on the carbon bearing the chloro sub-
stituent. In addition, the smaller fluoro substituent provides less steric hindrance to attack by the nucleophile.
A fluoro substituent is a stronger base than a chloro substituent, so elimination of the halogen in the second
step of the reaction is harder for a fluoro-substituted benzene than for a chloro-substituted benzene.
The fact that the fluoro-substituted compound is more reactive tells you that attack of the nucleophile on
the aromatic ring is the rate-determining step of the reaction.