Chemistry 110a
SECOND EXAM
October 4, 2013
Name (print)______________________________
A Valid Lewis Structure Note: Your exam should consist of 6 pages including the cover page, appendix, and grade
tabulation sheet. Skim the entire exam and solve the easiest problems first. Exams not returned
at the end of the period will not be graded.
PLEASE DO NOT OPEN THIS EXAM UNTIL YOU
ARE INSTRUCTED TO DO SO
1. Name the following compounds. (4 pts each)
2
CH3
(1S,3R)-3-methylcyclohexan-1-ol
(1R,3S)-1-methylcyclohexan-3-ol
(1R,3S)-3-methylcyclohexan-1-ol
OH
(a)
(1R,3S)-1-methylcyclohexan-3-ol
(b)
(a) _______________________________________________(IUPAC)
(b) (circle the correct name)
2. Consider the twist conformer for a 1,4 disubstituted
cyclohexane, written as shown (1 or 2) in the box at the
right: (a-g, 4 pts each)
(a) On either of the structures (1 or 2) provided,
indicate an interaction making this conformation
less stable than the chair conformation.
H
H
Br
CN
(b) Is this the highest energy twist conformation?
YES
1
NO
2
(c) In the box provided, draw the appropriate chair
conformation(s) for this compound. You can use
the bond-line drawing style used for structure 1.
(d) Use "axial" and "equatorial" at least once in your
drawing to demonstrate your understanding
of these descriptors.
(e) If appropriate, circle the more stable
chair conformation. (the appendix material may
be of some help!)
(f) Name the interaction you used to evaluate the
relative stability of the chair conformations, and label
your drawings to illustrate the interaction.
(g) This compound (1 or 2) contains 2 centers of
chirality in a sample held at room temperature.
c-f
TRUE / FALSE
3. Match the boiling point with the structure (4 pts)
CH3CH3
A. -89 °C
B. 49 °C
C. 106 °C
D. 126 °C
3
4. Circle the letter of the higher energy conformation in each pair. Estimate the energy difference (kcal/mol) between the
two conformations using appendix data. (10 points each)
H
CH3
H
CH3
H
H
CH3
H
CH3
Br
H
CH3
H
CH3
or
H
Br
H
CH3
or
CH3
CH3
CH3
H
A
B
C
D
5. The G° for the equilibrium between E and F shown below is +2 kcal/mol. Use this information to estimate the
energy cost of a 1,3-diaxial interaction between two methyl groups. Hint: use appendix information to quantitatively
estimate the familiar sources of strain in each conformer and combine these estimates with the measured G° value
(+2 kcal/mol) to solve for the diaxial Me-Me interaction. (10 pts)
CH3
CH3
G° = +2 kcal/mol
CH3CH3
H3C
CH3
E
CH3
F
Me-Me 1,3-diaxial
interaction (kcal/mol)
CH3
CH3
CH3
6. G° values are experimentally determined for substituted cyclohexanes by
spectroscopically measuring equilibrium concentrations of the two forms. For
the E/F equilibrium in question 5, what is the approximate (calculator not
required) concentration of each conformational isomer? (4 pts)
E:
F:
This is what you are
seeking to compute.
4
7. Consider the following pairs of structures. Designate each chirality center as R or S and identify the relationship
between them by describing them as representing enantiomers, diastereomers, constitutional isomers, or two
molecules of the same compound (Assume the molecules are at room temperature). 4 pts each.
H
CH3
Br
Br
H
H
F
H3C
CH3
CH3
H
F
CH3
CH3
H
Cl
Br
H
H
Br
Cl
H
CH3
CH3
CH3
F
F
F
F
8. A recent paper in Angewandte Chemie (2013, ASAP) reported the isolation of the analgesic tramadol from the
African peach tree. The bizarre thing about this observation is that before being isolated from a plant, Tramadol was
known only as a synthetic analgesic--discovered and made in the laboratory. The other curious thing about the plant
isolation is that racemic (+/-)-tramadol was recovered (living systems often produce chiral molecules). (10 pts)
(a) Designate each chirality center as R or S in tramadol isomer A. (2 pts)
OCH3
(b) In the box at lower left, write a bond-line structure of the other isomer of tramadol isolated
from the peach tree. (2 pts)
HO
(c) Draw the preferred (lowest energy) conformation of tramadol isomer A. Make sure your
drawing conveys a sense of the stereochemistry and three-dimensional character of the
molecule. The appendix material may be useful. (6 pts)
H
N
A
(b)
Monosubstituted Cyclohexanes - Thermodynamics
H H
H
H
H
X
G°
H
H
H
H
H H
H
H
HH
H
X
H
HH
H
H
H
Conformational Energies (A = G°, kcal/mol)
Appendix 1
D
0.008
CN
0.2
F
0.25
C CH
0.41
Cl
0.53
CH=CH2
1.49
Br
0.48
CH3
1.74
I
0.47
i-Pr
2.21
OH
0.6
Ph
2.8
OMe
0.58
C(CH3)3
4.7
OAc
0.7
Si(CH3)3
2.5
NH2
1.2
Sn(CH3)3
1.0
CO2H
1.4
HgOAc
0.0
CO2Na
2.0
MgBr
0.78
5
6
Chemistry 110a
SECOND EXAM
October 4, 2013
Name (print)______________________________
Page
Points
2
40
3
34
4
26
Total
100
Score