CHEM 122: Introduction to Organic Chemistry
Chapter 6: Chirality: The Handedness of Molecules.
1. Which of the following objects are chiral (assume that there is no label or other
identifying mark)?
a)
b)
c)
d)
e)
Pair of scissors
Tennis ball
Paper clip
Beaker
The swirl created in water as it drains out of a sink or bathtub.
2. 2-Pentanol is chiral, but 3-pentanol is not. Explain.
3. 2-Butene exists as a pair of cis-trans isomers. Is cis-2-butene chiral? Is trans-2butene chiral? Explain.
4. Which of the following compounds contain stereocenters?
a)
b)
c)
d)
2-Chloropentane
3-Chloropentane
3-Chloro-1-butene
1,2-Dichloropropane
5. Which of the following compounds contain stereocenters?
a)
b)
c)
d)
Cyclopentanol
1-Chloro-2-propanol
2-Methylcyclopentanol
1-Phenyl-1-propanol
6. Draw the mirror image for each molecule:
COOH
H
H2 N
C
H
CH3
a)
OH
b)
CH 2 OH
H
H
OH
O OH
H
HO
c)
H3 C
H
H
OH
d)
NH 2
7. Mark each stereocenter in these molecules with an asterisk. Note that not all
contain stereocenters.
OH
CH3
O
N
CH3
a)
OH
b)
O
O
OH
NH 2
c)
d)
8. Label all stereocenters in each molecule with an asterisk. How many
stereoisomers are possible for each molecule?
OH
CH2COOH
a) CH3CHCHCOOH
b)
CHCOOH
OH
c)
HO—CHCOOH
OH
d)
9. For centuries, Chinese herbal medicine has used extracts of Ephedra sinica to
treat asthma. The asthma-relieving component of this plant is ephedrine, a very
potent dilator of the air passages of the lungs. The naturally occurring
stereoisomer is levorotatory and has the following structure.
HO
H
C
H
NHCH 3
C
CH3
Ephedrine
a) Mark each stereocenter in ephedrine with an asterisk.
b) How many stereoisomers are possible for this compound?
c) The specific rotation of naturally occurring ephedrine is -41o. What is the
specific rotation of its enantiomer?
10. What is a racemic misture? Is a racemic mixture optically active? That is, will it
rotate the plane of polarized light?
11. Which of the eight alcohols with a molecular formula of C5H12O are chiral?
12. Write the structural formula of an alcohol with the molecular formula C6H14O that
contains two stereocenters.
13. Consider a cyclohexane ring substituted with one hydroxyl group and one methyl
group. Draw a structural formula for a compound of this composition that:
a) Does not show cis-trans isomerism and has no stereocenters.
b) Shows cis-trans isomerism but has no stereocenters.
c) Shows cis-trans isomerism and has two stereocenters.
14. Compound A (C5H8) is not optically active and cannot be separated into
enantiomers. It reacts with bromine in carbon tetrachloride to discharge the
orange color of bromine and form Compound B (C5H8Br2). When Compound A
is treated with H2 in the presence of a transition metal catalyst, it is converted to
compound C (C5H10). When treated with HCl, compound A is converted to
compound D (C5H9Cl). Given this information, propose structural formulas for
compounds A, B, C, D. Hint: There are at least three possibilities for Compound
A and, in turn, three possibilities for Compounds B, C, and D.
15. Following is a chair conformation of glucose, the most prevalent carbohydrate in
the biological world (Chapter 12).
HO HO
CH2OH
O
OH
OH
a) Identify the five stereocenters in this molecule.
b) How many stereoisomers are possible
c) How many pair of enantiomers are possible?