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Chapter 10 381
Copyright © 2017 Pearson Education, Inc.
67.
The product of each reaction is an alkene.
CH
3
CH
2
CHCH
3
OH
H
2
SO
4
CH
3
CH
2
CHCH
3
OH
H
CH
3
CH
2
CHCH
3
+
CH
3
CH CHCH
3
+
+
H
2
O
CH
3
CH
2
CHCH
3
Br
HO
−
CH
3
CH CHCH
3
+
H
2
O
+
Br
−
H
3
O
+
+
Recall that alkenes undergo electrophilic addition reactions, and the first step in an electrophilic addition
reaction is addition of an electrophile to the alkene.
The acid-catalyzed dehydration reaction is reversible, because the electrophile
1
H
+
2
needed to react with
the alkene in the first step of the reverse reaction is available.
The base-promoted elimination reaction of a hydrogen halide is not reversible, because an electrophile is
not available to react with the alkene in the first step of the reverse reaction.
68.
When
1
S
2
-2-butanol loses water as a result of being heated with sulfuric acid, the asymmetric center in the
reactant becomes a planar
sp
2
carbon. Therefore, the chirality is lost. When water attacks the carbocation, it can
attack from either side of the planar carbocation, forming
1
S
2
-2-butanol and
1
R
2
-2-butanol with equal ease.
OH
C
CH
3
CH
2
CH
3
H
+
H
+
OH
C
CH
2
CH
3
CH
3
H
+
OH
C
CH
3
CH
2
CH
3
H
H
+
+
OH
C
CH
2
CH
3
CH
3
H
H
+
OH
C
CH
3
CH
2
CH
3
H
(
S
)-2-butanol
(
S
)-2-butanol
(
R
)-2-butanol
C
CH
3
CH
2
CH
3
H
+
C
CH
3
CH
3
CH
2
H
+
+
H
2
O
OH
H
H
2
SO
4
CH
3
CH CHCH
3
+
H
3
O
+
69.
a.
CH
3
CH
2
CH CH
2
1. R
2
BH/THF
2. H
2
O
2
, HO – , H
2
O
−
CH
3
CH
2
CH
2
CH
2
OH
H
2
SO
4
O
CH
3
CH CHCH
3
+
H
2
O
1. O
3
,
78 °C
2. (CH
3
)
2
S
C
CH
3
2
H