Chapter 5
Stereoisomerism
Review of Concepts
Fill in the blanks below. To verify that your answers are correct, look in your textbook at
the end of Chapter 5. Each of the sentences below appears verbatim in the section
entitled Review of Concepts and Vocabulary.
• ______isomers have the same connectivity of atoms but differ in their spatial
arrangement.
• Chiral objects are not superimposable on their ____________________. The
most common source of molecular chirality is the presence of a
_______________, a carbon atom bearing ______ different groups.
• A compound with one chirality center will have one non-superimposable mirror
image, called its _______________.
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 5. The answers appear in the section entitled
SkillBuilder Review.
SkillBuilder 5.1 Identifying cis-trans Stereoisomerism
ASSIGN THE CONFIGURATION
OF THE FOLLOWING DOUBLE
BOND AS CIS OR TRANS
CHAPTER 5
79
SkillBuilder 5.3 Drawing an Enantiomer
NH
2
SHOW THREE WAYS TO
DRAW THE ENANTIOMER
OF THE FOLLOWING
COMPOUND. PLACE
YOUR ANSWERS IN THE
BOXES SHOWN.
SkillBuilder 5.6 Calculating % ee
The specific rotation of
optically pure adrenaline is
-53 . A mixture of (R)- and
(S)- adrenaline was found
to have a specific rotation
of – 45 . Calculate the %
ee of the mixture
=
observed [ ]
[ ] of pure enantiomer 100 %
% ee
100 %
=
CALCULATE THE
ENANTIOMERIC EXCESS
GIVEN THE FOLLOWING
INFORMATION:
=
×
×
80
CHAPTER 5
SkillBuilder 5.9 Assigning configuration from a Fischer projection
CH
2
OH
H OH
O OH
ASSIGN THE CONFIGURATION
OF THE CHIRALITY CENTER IN
THE FOLLOWING COMPOUND
Solutions
5.1.
a) trans b) not stereoisomeric
5.2. H
2
CCHCH
2
CH
2
CH
2
CHCH
2
=
Neither double bond exhibits stereoisomerism, so this compound does not have
any stereoisomers.
5.3.
a)
b)
5.4. All chirality centers are highlighted below:
a)
O
O
H
H
O
O
HO
OH
b)
HO
CHAPTER 5
81
5.5.
Br
Br
Br
Br
chirality center
5.6. The phosphorus atom has four different groups attached to it (a methyl group, an
5.7.
a)
HO
H
O
N
HOH
b)
O
OH
N
H
c)
O
O
HO
N
d)
OH
HO
H
O
NCH
3
H
82
CHAPTER 5
5.9.
a)
N
HOH
RS
b)
S R
C
l
Cl
B
r
Cl Br
5.10.
1
2
3
R
5.11.
P
12
3
4
S
5.12. specific rotation = [α] =
l
c
α
×
=
dm) (1.00mL) / g (0.0575
)1.47º(
×
+
= +25.6
CHAPTER 5
83
5.16.
[α] =
l
c
α
×
α = [α]
×
lc
×
= (+13.5)(0.100 g / mL)(1.00 dm) = +1.35 º
5.17.
=
o
b
s
e
r
v
e
d
[
]
[ ] of pure enantiomer 100 %
% ee
5.18.
o
b
s
e
r
v
e
d
[
]
% ee
=
5.19.
=
o
b
s
e
r
v
e
d
[
]
[ ] of pure enantiomer 100 %
% ee
=
84
CHAPTER 5
5.20.
Observed [
α
] =
l
c
α
×
=
dm) (1.00mL) / g (0.350
)º78.0(
×
+
= +
2.2
5.21.
a)
enantiomers
5.22.
There are three chirality centers, and only one of these chirality centers has a
different configuration in these two compounds. The other two chirality centers have the
same configuration in both compounds. Therefore, these compounds are diastereomers.
5.23.
a) yes b) yes c) no d) yes e) yes f) no
5.24.
5.23f has three planes of symmetry.
5.25.
CHAPTER 5
85
5.26.
a)
5.27.
Each of these compounds is a meso compound and does not have an enantiomer.
5.28
There are only four stereoisomers:
OH
OH
HO
OH
OH
HO
OH
OH
HO
not a chirality center
(see problem 5.5)
meso
86
CHAPTER 5
5.30.
O OH
O OH
O OH
5.31.
a)
HO H
H OH
CH
2
OH
HO H
O OH
S
R
S
b)
H OH
H OH
CH
2
OH
H OH
O OH
R
R
R
c)
H OH
HO H
CH
2
OH
H OH
O OH
R
S
R
5.32.
5.33.
NCH
3
OH
O
O
H
5.34.
a) Paclitaxel has eleven chirality centers.
b) The enantiomer of paclitaxel is shown below:
CHAPTER 5
87
5.35.
OH
HO
HO
t
r
a
n
s
n
o
t
s
t
e
r
e
o
i
s
o
m
e
r
i
c
n
o
t
s
t
e
r
e
o
i
s
o
m
e
r
i
c
5.36.
a) enantiomers
b) same compound
c) constitutional isomers
5.37.
a) 8 b) 3 c) 16 d) 3 e) 3 f) 32
5.38.
a)
OH
Cl
b) c)
88
CHAPTER 5
5.39.
a)
S
Me
Et OH
O
b)
S
NH
2
c)
R
Cl
5.40.
96%
ee
5.41.
a) diastereomers
b) diastereomers
c) enantiomers
5.42.
=
o
b
s
e
r
v
e
d
[
]
[ ] of pure enantiomer 100 %
% ee
CHAPTER 5
89
5.43.
a) True.
5.44.
specific rotation = [
α
] =
l
c
α
×
=
dm) (1.00mL) / g (0.0075
)º47.0(
×
−
= –
63
5.45.
a) (
S
)-limonene b) (
R
)-limonene c) (
S
)-limonene d) (
R
)-limonene
5.46.
5.48.
The first compound has three chirality centers:
R S R R
chirality
center
three chirality centers two chirality centers
This is apparent if we assign the configuration at C1 and C3 of the cyclohexane ring. In
the first compound, the configuration at C1 is different than the configuration at C3. As a
90
CHAPTER 5
5.49.
a) enantiomers
b) diastereomers
c) enantiomers
5.50.
a) -61
b) 90 %
ee
c) 95 % of the mixture is (
S
)-carvone
5.51.
a) chiral b) chiral c) achiral d) achiral
5.52.
[
α
] =
l
c
α
×
α
= [
α
]
×
lc
×
= (+24)(0.0100 g / mL)(1.00 dm) = +0.24 º
5.53.
a) optically inactive (meso)
b) optically active
5.54.
a)
OH
O
H
OH
b)
OH
O
H
OH
c)
OH
O
H
OH
d)
ClHO
e)
ClHO
CHAPTER 5
91
5.55.
a)
OH
O
H
OH
5.56.
OOH
HO H
OOH
HO H
OOH
5.57.
a) 3-methylpentane and 2-methylpentane are constitutional isomers.
b)
trans
-1,2-dimethylcyclohexane and
cis
-1,2-dimethylcyclohexane are diastereomers.
5.58.
The following two compounds are enantiomers because they are
CCC
H
H
H
H
5.59.
This compound will be achiral.
5.60.
a) This compound cannot be completely planar because steric hindrance prevents the two
5.61.
The compound is chiral because it is not superimposable on its mirror image.
CH
3
H
H
3
C
5.62.
This compound has a center of inversion, which is a form of reflection symmetry.
As a result, this compound is superimposable on its mirror image and is therefore
optically inactive.