Chapter 9
Addition Reactions of Alkenes
Review of Concepts
Fill in the blanks below. To verify that your answers are correct, look in your textbook at
the end of Chapter 9. Each of the sentences below appears verbatim in the section
entitled Review of Concepts and Vocabulary.
• Addition reactions are thermodynamically favorable at ____ temperature and
disfavored at _____ temperature.
• Hydrohalogenation reactions are regioselective, because the halogen is generally
placed at the ______ substituted position, called _______________ addition.
• In the presence of _____________, addition of HBr proceeds via an anti–
Markovnikov addition.
• The regioselectivity of an ionic addition reaction is determined by the preference
Review of Skills
Fill in the blanks and empty boxes below. To verify that your answers are correct, look
in your textbook at the end of Chapter 9. The answers appear in the section entitled
SkillBuilder Review.
9.1 Drawing a Mechanism for Hydrohalogenation
CHAPTER 9
173
9.4 Predicting the Products of Hydroboration–Oxidation
DRAW THE EXPECTED PRODUCTS OF THE FOLLOWING REACTION, AND DETERMINE THEIR RELATIONSHIP
+
RELATIONSHIP = _______________________
1) BH
3
THF
2) H
2
O
2
, NaOH
9.5 Predicting the Products of Catalytic Hydrogenation
H
2
Pt
DRAW THE EXPECTED PRODUCTS OF THE FOLLOWING REACTION, AND DETERMINE THEIR RELATIONSHIP
+
RELATIONSHIP = _______________________
174
CHAPTER 9
9.7 Drawing the Products of Anti Dihydroxylation
H
+
RELATIONSHIP = _______________________
1) MCPBA
2) H
3
O
+
DRAW THE EXPECTED PRODUCTS OF THE FOLLOWING REACTION, AND DETERMINE THEIR RELATIONSHIP
9.9 Predicting the Products of an Addition Reaction
DRAW THE EXPECTED PRODUCTS OF THE
FOLLOWING REACTION.
+
1) BH
3
THF
2) H
2
O
2
, NaOH
9.10 Proposing a One-Step Synthesis
OH
IDENTIFY REAGENTS THAT WILL ACHIEVE THE FOLLOWING TRANSFORMATION:
CHAPTER 9
175
Review of Reactions
Identify the reagents necessary to achieve each of the following transformations. To
verify that your answers are correct, look in your textbook at the end of Chapter 9. The
answers appear in the section entitled Review of Reactions.
O
H
X
Solutions
9.1.
a)
HBr Br
b)
HBr
R
O
O
R
Br
176
CHAPTER 9
9.3.
a)
H Br Br
Br
+
9.4.
a) b) c) d)
9.5. In this case, the less-substituted carbocation is more stable because it is resonance-
stabilized:
9.6.
a)
HBr
B
r
B
r
+
HCl Cl
CHAPTER 9
177
d)
HI
I
I
+
9.7.
a)
H Br Br
Br
H
Hydride
Shift
9.8.
Br
HBr
Br
Ring
Expansion
178
CHAPTER 9
9.9.
H
H Br
Methyl
Shift
This rearrangement converts a
9.10.
a) , because the reaction proceeds via a tertiary carbocation, rather than a
9.11.
a) To favor the alcohol, dilute sulfuric acid (mostly water) is used. Having a high
9.12.
a)
O OH
H O
H
HHOH
H
H
HOH
CHAPTER 9
179
9.13.
H O S O
O
O
H
HOMe O
Me
H OMe
HOMe
9.15.
a)
2) NaBH
4
1) Hg(OAc)
2
, H
2
O
OH
180
CHAPTER 9
c)
1) Hg(OAc)
2
, H
2
O
OH
9.16.
a)
2) NaBH
4
1) Hg(OAc)
2
, EtOH
O
E
t
9.17.
a)
1) BH
3
THF
2) H
2
O
2
, NaOH OH
9.18.
OH
1) BH
3
THF
2) H
2
O
2
, NaOH
CHAPTER 9
181
b)
1) BH
3
THF
2) H
2
O
2
, NaOH
OH
+ En
d)
1) BH
3
THF
2) H
2
O
2
, NaOH
HO
+ En
f)
1) BH
3
THF
2) H
2
O
2
, NaOH
H
OH
+ En
9.20.
9.21. Only one chirality center is formed, so both possible stereoisomers (enantiomers)
are obtained, regardless of the configuration of the starting alkene:
9.22.
182
CHAPTER 9
9.23.
a)
H
2
Ni
d)
H
2
Ni + En
9.24.
D
2
Pt + En
D
D
9.25.
CHAPTER 9
183
9.26.
a)
Br
2
Br
Br
+ En
Br
9.27.
a)
H
O
Br
+ En
b)
OH
Br + En
c)
OH
Br
+ En
9.28.
Br
2
OH
OEt
+ En
184
CHAPTER 9
9.29. The bromonium ion can open (before a bromide ion attacks), forming a resonance
stabilized carbocation. This carbocation is trigonal planar and can be attacked from
9.30.
a)
HO
OH + En
b)
OHHO
+ En
c)
OH
OH + En
9.31.
1) MCPBA
OH
OEt
2) [H
2
SO
4
] ,
+ En
9.32.
a)
MCPBA OH
3
O
+
OHHO
no chirality centers
CHAPTER 9
185
9.33.
a)
OsO
4
(catalytic)
NMO
OH
O
H
+ En
d)
KMnO
4
, NaOH
cold
OH
OH
186
CHAPTER 9
9.34.
a)
O
O
OO
H
1) O
3
2) DMS
c)
1) O
3
2) DMS
O
H
O
H
f)
1) O
3
2) DMS O O
9.35.
CHAPTER 9
187
c)
O O
1) O
3
2) DMS
9.36.
a)
1) BH
3
THF
2) H
2
O
2
, NaOH
OH
c)
1) CH
3
CO
3
H
2) H
3
O
+
HO
OH + En
f)
HBr
Br
g)
1) MCPBA
2) H
3
O
+
O
H
OH
+ En
188
CHAPTER 9
9.37.
OH
OH
9.38. The products are the same:
KMnO
4
, NaOH
cold
HO
OH
+ En
(2R,3R)
9.39.
1) BH
3
THF
2) H
2
O
2
, NaOH
+
1) O
3
2) DMS
OO
+
9.40.
a)
OH
+ En
1) BH
3
THF
2) H
2
O
2
, NaOH
CHAPTER 9
189
d)
H
2
Pt
e)
Cl
HCl
h)
9.41.
a)
HBr
ROOR
Br
9.42.
a)
C
l
Cl 1) NaOMe
2) HCl
190
CHAPTER 9
b)
OH
HO
1) TsCl, py
2)
t
-BuOK
3) BH
3
THF
4) H
2
O
2
, NaOH
9.43.
a)
Br 1) NaOMe
2) HBr, ROOR Br
9.45.
a)
2) NaOMe
1) HBr
CHAPTER 9
191
9.46.
a)
1) HBr, ROOR
2) t-BuOK
b)
1) HBr
2) NaOMe
9.48. A reaction is only favorable if ∆G is negative. Recall that ∆G has two
components: (∆H) and (-T∆S). The first term (∆H) is positive for this reaction (two
9.49.
KMnO
4
1) Hg(OAc)
2
, H
2
O
HO OH
+ En
HO
192
CHAPTER 9
9.50.
1) MCPBA
2) H
O
+
1) BH
3
THF
2) H
O
, NaOH
OH
HO
OH + En
9.51.
a)
H O
H
HHOHHOH
O
H
H OH
c)
Br
H Br Br
CHAPTER 9
193
9.52.
9.53.
1) HBr
b)
2) t-BuOK
1) HBr, ROOR
9.54.
OH 1) Conc. H
2
SO
4
2) HBr, ROOR
3) t-BuOK
9.56.
1) MCPBA
2) H
3
O
+
Compound A
OH
OH
9.57.
194
CHAPTER 9
b)
Br
Br
1) NaOMe
2) HBr, ROOR
1) NaOMe
2) HBr
9.58.
a)
1) HBr, ROOR
2)
t-
BuOK
9.59.
NaOMe
Compound A
dilute H
2
SO
4
Compound B
Br
Compound C
OH
CHAPTER 9
195
9.60.
Br + En
HBr, ROOR
9.61.
excess H
2
Pt +
D
i
a
s
t
e
r
e
o
m
e
r
s
9.62. Markovnikov addition of water without carbocation rearrangements can be
achieved via oxymercuration-demercuration:
9.63.
O
H O S O
O
O
H
O
H
HOMe OH
O
H
Me MeO
OH
HOMe
196
CHAPTER 9
9.64.
a)
H O
H
H
HOH
Methyl
Shift
9.65.
H
2
(PPh
3
)
3
RhCl
c)
1) BH
3
THF
2) H
2
O
2
, NaOH
OH
CHAPTER 9
197
9.66.
a) Hydroboration-oxidation gives an anti-Markovnikov addition. If 1-propene is the
starting material, the OH group will not be installed in the correct location. Acid-
9.67.
Br
2
Br
Br Br Br
(meso)
9.69. The reaction proceeds via a resonance-stabilized carbocation, which is even lower
in energy than a tertiary carbocation:
198
CHAPTER 9
9.70.
OH Br
HBr
ROOR
OH
OH
Cl
2
HBr Br
2
H
2
O
Cl
1) BH
3
THF
2) H
2
O
2
, NaOH
OsO
4
, NMO
CHAPTER 9
199
9.71.
O
HO OH
HO
Br
HBr
ROOR
1) BH
3
THF
2) H
2
O
2
, NaOH
1) O
3
2) DMS
9.72. Addition of HBr to 2-methyl-2-pentene should be more rapid because the reaction
can proceed via a tertiary carbocation. In contrast, addition of HBr to 4-methyl-1-
pentene proceeds via a less stable, secondary carbocation.
9.73.
HS
9.74.
OH
1) NaOMe
200
CHAPTER 9
9.75.
H
2
Pt OH
2,4-d imethy lpentan-1-olCompound X
1) BH
3
THF
2) H
2
O
2
, NaOH
9.76.
Cl t-BuOK HBr Br Br
+ +
B
r
9.77.
9.78.
H
H
CHAPTER 9
201
9.79.
a)
O
OH
H O S O
O
O
H
O
OH
H
b)
O
H O S O
O
O
H
O
H
202
CHAPTER 9
9.81.
a)
Br
Br
OH OH
Br
O
H
Br
Br
O
Br
9.82.
OH
OO
I
O
I
I
I
OH
O
I
O
I
O
H