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ORGANIC CHEMISTRY (CH_334_001_F2011)
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1. Multiple Choice: The sugar ribose is shown in a Fische...
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Points: 1
The sugar ribose is shown in a Fischer projection below. The correct assignment of
configuration is:
a. 1-R, 2-R, 3-R
b. 2-R, 3-R, 4-R
c. 2-R, 3-S, 4-R
d. 2-R, 3-R, 4-S
2. Multiple Choice: A stereoselective reaction (which I w...
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Points: 1
A stereoselective reaction (which I will not specify) creates a mixture of two
enantiomers: 95% of one, and 5% of the other. The enantiomeric excess in this reaction
is:
a. 95%
b. 5%
c. 90%
d. 100%
3. Multiple Choice: In the monobromination of 3-methylhep...
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Points: 1
In the monobromination of 3-methylheptane, the stereochemical outcome of the
reaction is:
a. A single enantiomer.
b. A pair of enantiomers in a 1:1 mixture (racemic).
c. A pair of enantiomers with one being formed in an ee > 0.
d. Two diastereomeric pairs of enantiomers, 4 stereoisomers total.
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4. Multiple Choice: Monochlorination of methylcyclohexane...
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Points: 1
Monochlorination of methylcyclohexane gives which outcome, including sterochemical
isomerism?
a. A single enantiomer of one isomer.
b. Two enantiomers of one regioisomer.
c. 5 regioisomers, each in a single enantiomer.
d. A total of 12 regio- and stereochemically distinct isomers.
5. Multiple Choice: Imagine the 1-phenylethyl radical (Ph...
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Points: 1
Imagine the 1-phenylethyl radical (Ph(CH3)CH·) reacting with chlorine (Cl2). Select the
answer that best relates the stereochemical outcome to a potential energy diagram.
a. A given molecule of the radical will have a fixed stereochemical configuration at
carbon, so there is only a single pathway available to produce a single enantiomer.
b. The planar radical can be approached from either side to give two different
transition states leading to the two enantiomers. Because these two have identical
energies (they are enantiomeric), a racemic product is formed.
c. The planar radical can be approached from either side to give two different
transition states leading to the two enantiomers. However, because these two have
different energies (they are diastereomeric), one enantiomer of the product is formed
in preference to the other.
d. The delocalized radical provides a mechanism for placing chlorine at every carbon
in the molecule.
6. Multiple Choice: Choose the best method for determning...
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Answer
Points: 1
Choose the best method for determning the ee if I try to stereoselectively make
R-1-phenyl-1-chloroethane (shown below).
a. Measure the melting point, since this will vary linearly with ee.
b. Measure the boiling point, since this will vary linearly with ee.
c. Measure the rotation of plane-polarized light by the product, even if I don't know
the rotations of the pure enantiomer.
d. Perform chromatography on a chiral medium, as the interactions between
enantiomeric molecules and the chiral medium creates a diastereomeric relationship
that allows separation and measurement.
7. Multiple Choice: How do the outcomes for monobrominati...
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Answer
Points: 1
How do the outcomes for monobromination of the two isomers (cis, trans) of
1,3-dimethylcyclohaxane compare?
a. Stereochemically distinct radical intermediates lead stereospecifically to
diastereomeric products, one from each isomer.
b. The cis isomer gives one stereoisomer in a stereoselective reaction but the trans
isomer is nonstereoselective and gives a mixture.
c. Both isomers give the same intermediate, which produces identical mixtures of
products from each isomer. The reaction is slightly stereoselective, but
nonstereospecific.
d. Each isomer gives a different mixture of products, and is thus stereospecific but
not highly stereoselective.
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8. Multiple Choice: 4-chloromethylcyclohexane can be isol...
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Points: 1
4-chloromethylcyclohexane can be isolated as either of two different stereoisomers.
What is their relationship?
Answer
a. Diastereomers (cis/trans).
b. Enantiomers (4-R, 4-S).
c. Enantiomers (1-R, 1-S).
d. Racemates.
9. Multiple Choice: How do enzymes accomplish enantiosele...
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Points: 1
How do enzymes accomplish enantioselective reactions?
Answer
a. They can turn racemic products into diastereomeric derivatives, one of which the
organism will not use.
b. Enzymes are chiral molecules, so production of different enantiomers within the
enzyme will have different potential energy curves.
c. Enzymes cannot react with achiral molecules.
d. Enzymes incorporate self-correction chemistry to turn the "wrong" enantiomer into
its mirror image.
10. Multiple Choice: An enzyme called "chloroperoxidase" c...
Points: 1
Question An enzyme called "chloroperoxidase" can catalyze the following conversion using free radical
chemistry. Select the most likely mechanism by which this enzyme achieves enantioselectivity.
Answer
a. Creation of a chiral radical intermediate.
b. Equilibration of enantiomeric products in a chiral environment.
c. Differential metabolism of the enantiomeric products.
d. Selective delivery of the chlorinating agent to one face of the radical intermediate.
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