Chemistry 51 DS
Quiz 2/26/99
1. What is the name of the molecule below
H
Cl
FH2C
C
F
In each of the following molecules classify each chiral carbon as R or S.
2.
CHO
CH2F
HO
CH3
3.
CHO
F
CF3
F
Cl
H
4 Complete the saw horse type diagram based on the Fischer Projection
Cl
H
OH
H
Br
Cl
Br
Cl
5. If the pure R form of a molecule has a specific rotation of -30 and you a given a mixture
of the two enantiomers which has a specific rotation of +20 degrees
a) which enantiomer is present in excess?
b) what is the optical purity of the mixture
Chemistry 51 DS
Quiz 3/3/99
In each of the following molecules classify each chiral carbon as R or S.
1.
H
C
Cl
CH3
F
2.
CHO
HO
H
CH3
3.
CHO
F
H
F
CHO
H
4 Draw the following as a Fischer Projection
F
H
Cl
H
Cl
Cl
F
Cl
5. If the pure R form of a molecule has a specific rotation of -60 and you a given a mixture
of the two enantiomers which has a specific rotation of +40 degrees calculate
a) the compostion of the mixture in terms of the percentage of the R and S enantiomers
b) the optical purity of the mixture
Chemistry 51
Oct. 2. 1998
Give products of the following reactions showing stereochemistry, Indicate whether
each structure is optically active (A) or inactive(I).
CH3
1.
H2,Ni
CH3
2.
CH3
CH3
H
F
H
Cl2
light
F
use Fischer projections
3. Pure R 1-chloroethanol has a specific rotation of 50. A particular sample of 1-clhloroethanol
has a specific rotation of -25.
What is the optical purity?
What is the percentage of R stereoisomer in the sample?
What is the percentage of S stereoisomer in the sample?
Quiz No. 3
Chemistry 51 DT
1. What are the products of the free radical monochlorination of methyl cyclopropane. Show
all unique stereochemical isomers that are produced, Indicate which are optically active. (A)
and which are optically inactive (I). Be mindful of the three dimensional structure of the parent
molecule. Several skeleton outlines are given for the answers. If racemic pairs are produced
circle the pairs.
Cl2
CH3
2. R 2-bromobutane has a specific rotation of +50.0 . When you visit the stockroom Carl gives
you 100 mL of 2-bromobutane that has a specific rotation of -40.0 (financial crisis, you know).
a) What is the percent composition in terms of R and S enantiomers?
%R =
%S =
When your bromobutane is reacted with isotopically labelled sodium bromide
for a short period of time and the bromide is analyzed it is found that 10.0% of the
2-bromobutane is now isotopically labelled and that the specific rotation has dropped
to -34.0
RBr + Na*Br
R*Br + NaBr
b) What fraction of the original bromobutane has undergone reaction?
c) What fraction of the 2-bromobutane has reacted with inversion of configuration?
What fraction with retention?
% inversion =
%retention=
Chemistry 51 DS
9/22/99
Shown below is a Fischer projection of 1 R,2 S 2-bromo-1-chloro-2-fluoro-1-iodoethane, 1.
H
I
Cl
Br
F
H
1
Classify each structure below by its relationship to 1. Use the letter S
for the same, E for enantiomer, D for diastereomer, M for meso, X for any other
relationship. Note that conformational differences are unimportant in this question.
H
I
I
F
Br
H
Cl
H
Cl
Cl
H
H
Br
H
I
F
H
Br
F
H
Cl
I
F
Br
H
H
Br
I
F
Cl
R1-chloro-2-methylbutane, 2, is monochlorinated and the product mixture is carefully distilled.
During the distillation compounds are collected at several different boiling points.Each such collection
is called a fraction. What are the expected monochloroproducts? Use the partial Fischer
projections below. Keep the Cl of the original molecule at the top of the diagram.Indicate
which compounds will be distilled in the same fraction by circling the compounds that have the same
boiling point. Indicate by the letter I or A if each fraction is optically inactive or active. Assume
no rearrangement.
CH2Cl
CH3
H
H
H
CH3
2
Chemistry 51 DX
Quiz no. 2
1. Using the graph provided below sketch the potential energy curve for rotation
about the C2-C3 bond of 2-methylbutane. The starting conformation, 0 degrees rotation,
is provided for you below. Be very careful about showing relative energy levels.
H
CH3
H
H
CH3
E
CH3
0
180
90
270
360
2. What is the major product for
2-methylpropane subjected to monobromination (relative reactivities are 1:80:1200)
CH3
3. Consider the following molecules.
CH3
2-bromobutane
Br
CH3
H
Br
H
CH3
CH3
A
B
C
Which are compounds that may exhibit optical activity in the lab
(for which enantiomers may exist)? Answer by letter
4.Compound X is optically active. The pure R form has a specific rotation of +50. What is
the expected specific rotation of a mixture formed from 10.0 g of the R form and 20.0 g of the
S form?
Chemistry 51 DX
Quiz 3
February 24 2000
Classify the chiral carbon in the following molecules as R or S. (2 pts correct answer, -1
for each wrong answer, probably not a good idea to make random guesses)
1.
Cl
C
Br
F
H
2.
H
Br
C
Cl
F
H
3.
Cl
F
Br
4. (4 pts) Show all steps in the synthesis of 2,2-dimethylpropane from alcohols
having four or fewer carbon atoms.
Chem 51
Quiz 4
What are the unique products of the following reaction? Show stereochemistry.
CCl3
H3 C
H
H
CH3
Cl2
light
CCl3
C6H7Cl7
Circle which of the following structures are the same as compound A. Draw a box around
those that are enantiomers of A
CH3
F
H
F
H
CH3
A
CH3
F
H
F
H
CH3
CH3
H
CH3
H
F
F
F
H3 C
H
CH3
H
F
CH3
H F
F
H
CH3
Optically pure R 2-butanol has a specific rotation of 50 degrees. A particular
sample of 2-butanol has a specific rotation of -20. What is the make-up of the
sample in terms of the R and S stereoisomers?
Chemistry 51
Quiz 3, February 26 2002
1. Which is the relationship of compounds 1 and 2 to compound A. Answer by a letter:
S for the same compound, E for enantiomer, D for diastereomer, O for other.
Cl
H
Br
Cl
H
Br
Br
H
Cl
Br
Cl
H
Cl
1
H
Br
Cl
Br
H
2
A
2. Circle and classify each chiral carbon in the following molecules as R or S. If the compound
is optically active put an X in the box
CHO
H
H
Br
Br
CO2H
Br
H
CO2H
Br
Br
H
F
H
F
CHO
Cl
H
H
H
3. What are the major monobromo products of the following reaction? Give stereochemistry.
CH3
C2 H5
H
H
C2 H5
CH3
Br2
heat
Chemistry 51
Quiz 3, February 25, 2003
Classify each chiral carbon in the following molecules as R or S.
Br
F
1.
CH3
Is this compound optically active?
CH 3
Br
F
OH
2.
H
Is this compound optically active?
CH 3
HO
H
CH 3
3. Use one or more Fischer projections to show the products of the following reaction. If a careful
fractional distillation is done of the product mixture how many fractions will
be obtained? Indicate which, if any, of the fractions will be optically active?
H
C 2H 5
CH2
Br
CH 3
HBr
CH3
ionic conditions
C 2H 5
(S) 6-Bromo-3,6-dimethyl-oct-3-ene
Chemistry 51
Sept 24 2003
Quiz 3
1. Provide a synthesis to convert methane to deuteriomethane, CH3D. You may use
methane, inorganics and any solvents of your choice.
2. Complete the structure given to show the most stable conformation of 2-methyl butane
about the central C2-C3 bond.
3. a) The specific rotation of R 2-chloro butane is - 60. What will be the specific rotation
of a mixture which is 80% S enantiomer and 20% R enantiomer.
b) What is the optical purity of the mixture?
4. Classify each chiral carbon below as R or S.
F3C
F
CO2H
H
HO
CH3
Cl
H
5. Name each compound in 4 above including the stereochemical designation.
Chem 51, Fall 2004, evening
9/27/2004
1. A mixture of the enantiomers of 2 chlorobutane has the make up shown below
CH3
CH3
H
Cl
Cl
H
C2H5
C2H5
16 grams
8 grams
The pure R enantiomer has a specific rotation of 33 degrees.
a) What is the specific rotation of the mixture?
b) What is the optical purity of the mixture?
2. Name the following compound including the designation of configuration.
HO
Cl
HO
Cl
CO2H
CO2H
3. What is the specific rotation of the compound above? If you cannot
assign a numerical value to the specific rotation can you tell if the specific rotation
is positive or negative?
4. Using Fischer projection diagrams draw all stereoisomers of CH3CHFCHBrCHFCH3.
Circle those that are optically active.
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
use as many of the above templates as needed.
Chemistry 51, Fall 2004
Quiz 4
What are the products of the following reactions? You must show stereochemistry.
Circle the products that are optically active.
1.
H 3C
CH3
H2
catalyst
H3 C
CH3
2.
excess H2
catalyst
3. For the following reaction answer the questions below
CH3
Cl2
H3 C
CH3
uv
H3 C
a) Upon fractional distillation of the product mixture how many fractions are obtained?
b) How many fractions consist of more than one compound?
c) How many fractions consist of a racemic mixture?
d) How many fractions are optically active?
Quiz 2
Chemistry 51, Fall 2005
1. An optically impure sample of 2-bromobutane has a specific rotation of 10 degrees. Optically
pure R 2-bromobutane has a specific rotation of 25 degrees. If 10.0 grams of the impure
mixture are resolved (separated into individual enantiomers) and 1.0 grams of the R enantiomer
is obtained what is the percent yield for the resolution?
2. Classify each chiral carbon as being R or S
OH
H
CH3
H
F
Br
Cl
H
C2H5
Br
front____
rear_____
H
Cl
3. What are the products of the following reactions? Show stereochemistry
H2
catalyst
Cl2
light
Quiz 3, Chemistry 51, Spring 2007
1. Cis 1,2 dimethyl cyclohexane is shown below on the left. Being mindful of the reapidly occuring
ring flip process, classify each of the other compound's relationship to cis 1,2 dimethyl cyclohexane
by the following code: S for same compound, C for constitutional isomer, E for enantiomer, D for
diastereomer.
cis 1,2 dimethylcyclohexane
2. Do as in the question above for the reference compound on the left below
H
H
Br
Br
F
Cl
H
Cl
F
Reference
Br
H
Cl
F
Br
Cl
F