Exam 2
Name __________________________
CHEM 210
1. (8 pts) Draw both the cis and trans isomer of 1-chloro-2-ethylcyclohexane (pictured), each as a pair of
chair conformers. Which isomer is most stable and why?
Cl
Cl
Cl
Cl
both have one axial, one eq.
cis-
Cl
Cl
Cl
both eq.
trans-
since this isomer can achieve
a diequitorial conformation, it is
lower in potential energy
2. (8 pts) Consider 1-bromo-2-methylpropane (shown).
Br
a. On the templates below, draw the most stable conformer and
1
2
calculate the total interaction energy.
b. Draw the least stable conformer and calculate the total interaction energy.
c. Label each drawing as staggered or eclipsed overall and indicate any gauche or
anti-relationships within each conformer.
d. What is the total barrier to rotation? ________________ kcal·mol-1
Most stable
Interaction
H,H eclipsed
H,CH3 eclipsed
H, Br eclipsed
CH3, Br gauche
CH3, Br eclipsed
Least Stable
gauche, 0.9 kcal/mole
4.8
CH 3
Br CH 3
Br
H
H
H
CH 3
Br, CH 3 are anti
H
1.0
H
H
CH 3
1.4
eclipsed: H,H is
4.8 + 1.4 + 1.0 = 7.2
3. (6 pts) Assign R or S configurations to all of the chirality centers in the anti-hypertension agent, Captopril®:
S
S
Other copies of the
molecules for scratch work
(final answers must be on
structure to left!).
kcal·mol
1
1.4
1.8
0.9
4.8
-1
4. (10 pts) Pseudofed® is an over-the-counter antihistamine that also acts as a stimulant. Draw all possible
stereoisomers of Pseudofed® and label the inter-relationships between all of them. Assign R & S
configurations to every center. The benzene ring can be abbreviated as –Ph.
HN
Enantiomers
HO
HN
(R)
NH
(S)
OH
(R)
(S)
Diastereomers
HO
HN
(S)
NH
(S)
(R)
OH
(R)
Enantiomers
5. (16 pts) Name the following compounds using IPUAC nomenclature:
a.)
2,3,3-trimethylhexane
b.)
4-sec-butyl-1,1-dimethylcycloheptane
c.)
4-methylcyclopentene
d.)
cis-6,6-dimethylhept-2-ene
OH
OH
e.)
5-isopropyl-6-methyloctan-3-ol
f.)
4-methylcyclohexanol
h.)
5-ethyl-3-heptyne
Br
g.)
9-bromobicyclo[3.3.1]nonane
CH 3
H
H
i.)
OH
CH 3
3-methyl-2-pentanol
OH
6. (10 pts) Draw the following compounds:
a.) isobutylcyclooctane
b.) trans-4-methyl-2-octen-1-ol
c.) 4,4-dimethyl-1-pentyne
OH
d.) 6-methylbicyclo[3.1.0]hexane
e.) cis-1-iodo-2-butene
f.) S-2-butanol
OH
H
I
CH 3
H 3C
H
H
As a Newman projection using C2/C3 bond
7. (8 pts) How is each compound related to the simple sugar D-erythrose? Is it an enantiomer, diastereomer or identical?
H
a.
OH
OHC
OH
OHC
H
(S)
HO
(R)(R)
OH
HO
b.
HO
CHO
H
D-erythrose
c.
(S)
HO
H
OH
H
Diastereomer
H
Diastereomer
NH 2
NH 2
b.
NH 2
A
Diastereomer
Identical
OH
(R) (S)
HO
Enantiomer
9. (8 pts) How is compound A related to compounds a. through d.?
constitutional isomers or identical molecules.
H
OHC
H
OH
H
8. (8 pts) Consider Newman projections (A-D) for four carbon carbohydrates:
CHO
CHO
CHO
CHO
H
HO
H
H
H
OH
OH
OH
H
H
HO
HO
OH
OH
H
H
OH
OH
OH
OH
A
B
D
C
a.
OH
(S) (S)
HO
OH
d.
H
OHC
(R)
(R)
OH
Diastereomer
How is each pair related?
a.
A and B? Identical
b.
A and C? Enantiomers
c.
A and D? Diastereomers
d.
C and D? Diastereomers
Choose from enantiomers, diastereomers,
c.
d.
NH 2
Enantiomer
NH 2
Const. Isomer
10. (8 pts) Assign one true statement (A. to F.) to each of the following compounds. Answers (A. to F.) may be used
more than once or not at all.
OH
Cl
OH
HO
OH
C
OH
E (meso)
D
A. Has a mirror image but no enantiomer
B. Has a mirror image that is a diastereomer
(impossible)
C. Has an enantiomer and no diastereomer
Cl
D
A
D. Has both and enantiomer and diastereomer
E. Has a diastereomer but no enantiomer
F. Has no constitutional isomers (this is
impossible for these compounds)
11. (5 pts) Compare the structure of cyclodecane in an all-chair conformation
with that of trans-decalin. Explain why all-chair cyclodecane is highly
strained and yet trans-decalin is nearly strain free.
all-chair cyclodecane
trans-decalin
There is only one difference between the two compounds as represented.
The all-chair cyclodecane has two hydrogens pointing inwards at the place where trans-decalin has a C-C bond. The
C-C bond makes the favored chair conformer of trans-decalin more rigid; while the two inward pointing H’s in all chair
cyclodecane introduces steric hindrance – two atoms vying for the same space.
12. (5 pts) Consider the following compounds:
A
B
C
a. Which of the following compounds are chiral? A,B and C
b. Which, if any are meso? None
c. Which, if any does not have a possible diastereomer? D, not chiral
Score ________/100 Approx. Course Grade:
A
A-
B+
B
B-
D
C+
C
D
F