CHM 225: Organic Chemistry I
Exam IV
Name: ________________________________________________
16 May 2013
This exam will be graded out of 100 possible points.
Your score on this exam will be worth 15% of your total CHM 225 grade.
Question #
Points possible
1
6
2
4
3
20
4
12
5
6
6
16
7
17
8
7
9 10
12 4ec
This exam is 7 numbered pages, including this page
Any form of cheating or attempted cheating or copying will result in a grade of zero on the exam, and may lead
to further disciplinary action.
1. (6 points) Analyze the following molecules to determine whether they are aromatic, nonaromatic, or antiaromatic.
Molecule
Aromaticity
a.
Aromatic
Non-aromatic
Antiaromatic
b.
Aromatic
Non-aromatic
Antiaromatic
c.
Aromatic
Non-aromatic
Antiaromatic
2. (4 points) Name the following molecule, using cis/trans.
1
3. You are working in lab with Prof. Martian and your mildly incompetent lab partner Ben Zene.
Prof. Martian gives you each a molecule to work with: constitutional isomers with the formula
C4H8O2.
a. (8 points) Ben decides to smell his. He immediately recoils, gags, and says “That’s
nasty!” You feel bad for him and you help him take the IR and 13C NMR spectra, which
are shown below.
IR
Major peaks
3030 cm–1
2971 cm–1
1712 cm–1
13
C NMR
DEPT info:
14 ppm: methyl group
18 ppm: methylene (CH2) carbon
36 ppm: methylene carbon
181 ppm: carbon attached to no hydrogens
Propose a structure for Ben’s molecule.
A brief justification is recommended but not required
2
b. (12 points) Now, consider your molecule (also C4H8O2). It does not smell unpleasant,
nor does it smell fruity. Your spectra are shown below:
IR
Major peaks
3466 cm–1
2985 cm–1
2938 cm–1
1718 cm–1
13
C NMR
DEPT info:
19 ppm: methyl group
25 ppm: methyl group
73 ppm: carbon attached to 1 H
211 ppm: carbon attached to no H
Determine the structure. Describe your logic: Why does the structure you propose fit the data?
Hint: it is NOT a carboxylic acid.
A justification is required for full credit.
3
4. (12 points) Upon returning to your lab bench, you discover that Ben Zene has been goofing off,
and accidentally mixed two other compounds (both C6H14O; structures shown below) together.
Prof. Martian is livid.
Dipropyl ether
1-hexanol
a. Ben offers to purify the chemicals by column chromatography. Which of the chemicals
will have a higher Rf value? (Give a 1-sentence explanation).
b. Prof. Martian tells Ben that a distillation would be much more appropriate.
i.
The compounds have boiling points of and 89 C and 157 C. Which
compound has the lower boiling point? Why?
ii.
Which type of distillation should Ben try first: simple, fractional, or steam
distillation? Explain briefly.
5. (6 points) The molecule imidazole (shown below) is a weak base; upon exposure to a strong
acid, it is protonated. Predict the structure of protonated imidazole, and explain your choice.
Imidazole
A
H+
Explanation:
4
B
6. Prof. Martian tells you to synthesize the following compound from ethyl acetate.
a. (5 points) What is the hybridization (sp, sp2, or sp3) on the oxygen atom in the ring?
Justify your answer.
b. (2 points) Draw the other starting material in the reaction below
c. (8 points) Draw a complete electron-pushing mechanism.
+
-------------------------
+
d. (1 point) This synthesis is an example of a
A. Saponification
B. Transesterification
5
7.
(17 points) Consider the molecule at right.
a. Use the templates below to draw a Newman projection of one of the chair conformers.
b. Draw the two E2 products of the following reaction. Show stereochemistry.
You do not need to show a mechanism.
c. Draw the product of the following reaction, showing all stereocenters
You do not need to show a mechanism.
d. Consider the product above (part c.). Draw both chair structures of this molecule, using
the templates provided. Clearly show whether a substituent is axial or equatorial.
e. The more stable conformer is the
8.
Left
Right
one (circle one).
(7 points) Consider the following molecule (shown as a Fischer Projection).
a. Assign the stereocenter: R
b. The molecule is:
D
L
c. Name the molecule:
6
S
9. (12 points) Consider the following intramolecular Fischer esterification. Draw a mechanism.
10. (4 points Extra Credit). Consider a different route to the same product. This mechanism is not a
Fischer esterification. Draw the structure of the starting material. Draw the intermediate
(what’s the NaHCO3 for?) and describe the mechanism.
7