CHE231 SSCC – Exam III
Organic Chemistry
Monday, November 27th, 2006
Name ______
Multiple choice section (20pts-2pts each). Please circle your answers.
1. Molecules which contain stereogenic centers and a plane of symmetry are called:
A)chiral molecules
B)enantiomers
C)diastereomers
D)meso compounds
2. Which atom is acting as an electrophile in the following reaction?
A)The O atom of the cyclohexanone
B)The C atom of CN-
C)The N atom of CN-
D)The double-bonded C atom of cyclohexanone
3. A sample of 2-methyl-1-butanol has a specific rotation of [] = +1.151.
(S)-(-)-2-methyl-1-butanol, [] = - 5.756 and (R)-(+)-2-methyl-1-butanol, [] = +5.756. What is the actual stereoisomeric composition of the mixture above?
A)80% (R), 20% (S)
B)20% (R), 80% (R)
C)50% (R), 50% (S)
D)60% (R), 40% (S)
E)40% (R), 60% (S)
4. (R) -2-chlorobutane is represented by:
A)I
B)II
C)III
D)IV
E)V
5. The two compounds shown below are
A)Enantiomers.
B)Diastereomers.
C)Constitutional isomers.
D)Identical.
E)Different but not isomeric.
6. Which one of the following can exist in optically active forms?
A)cis-1,3-dichlorocyclohexane
B)trans-1,3-dichlorocyclohexane
C)cis-1,4-dichlorocyclohexane
D)trans-1,4-dichlorocyclohexane
E)cis-1,2-dichlorocyclohexane
7. The activation energy (G‡)
A)is always a negative quantity in terms of free energy change.
B)is the energy difference between reactants and products.
C)is the energy difference between reactants and transition state.
D)is the energy difference between products and transition state.
8. Identify the leaving group in the following reaction:
A)CH3OH
B)CH3OH2+
C)CH3OCH3
D)H2O
E)None of the above
9. How many stereogenic centers are there in the anabolic steroid methenolone?
A)4
B)5
C)6
D)7
E)8
10. Consider the pair of stereoisomers pictured. These stereoisomers are:
A)enantiomers
B)diastereomers
C)meso compounds
D)identical
Short answer section (30pts).
- (10pts) A) Draw all the stereoisomers for 3,4-dibromohexane. Draw them as Fischer projections.
B) Which pairs of the above compounds are (if none, then write none):
Enantiomers:BC
Diastereomers:AB, AC
Meso:A
12. (6pts) What is the relationship of the structures in each pair? Label them as enantiomers (E), diastereomers (D), constitutional isomers (C), or Identical (I).
A)
Diastereomers
B) Identical
C) Enantiomers
13. (7pts) Circle the statements that are true regarding enantiomers and diastereomers:
A)A pair of enantiomers are not mirror images of each other.
B)A racemic mixture is a mixture containing an equal amount of 2 enantiomers.
C)A pair of diastereomers will have the same boiling points and melting points.
D)A pair of enantiomers will rotate plane-polarized light in opposite directions.
E)A pair of enantiomers will have the same molecular weight.
F)A pair of enantiomers will react at the same rate with a chiral enzyme.
G)A pair of diastereomers are superposable on each other.
14. (7pts) Below is the free energy diagram for the SN2 reaction of (R)-2-chlorobutane with hydroxide ion:
A)Draw the structures which correspond to A, B, and C in the free-energy diagram above for the reaction of (R)-2-chlorobutane with hydroxide ion. Include stereochemistry if applicable.
+3 structures A and C
+1 structure B
B)Label the free energy of activation (G ‡ ) and free energy change (G) on the diagram above.
C)Is the reaction exergonic or endergonic? exergonic