Exam II
004:121
Organic I
Spring 2007
3/21/07
Exam II Last Name ______________________ First Name ______________________ (PRINTED) (PRINTED) UI ID #
_________________________________
Write your name on each page. Please read each question carefully before answering. Answer the questions in ink in the spaces provided inside. If you make changes as you go, please make sure your final answer is clearly indicated. You have 90 min. Good Luck! _______________________________________________________________________
Grading: Q.#
Score
(Max)
1.
__________ (30 pts)
2.
__________ (14 pts)
3.
__________ (16 pts)
4.
__________ (32 pts)
5.
__________ (8 pts)
Total:__________ (100 pts)
Chem. 121
Exam II (3/21/07)
Name_____________________________________
1.
(3 pts each) Please circle one answer for each question.
A.
How many chiral centers are present in the following compound? A. 0 B. 1 C. 2 D. 3 E. 4
B.
Designate the following stereogenic centers as R or S (from left to right). A. R,S. B. S,S. C. S,R. D. R,R. E. None of the above. CH3 A H HO
Consider the following pairs of molecules:
C. Which pair of molecules represents a pair of enantiomers?
B
D. Which pair of molecules represents constitutional isomers? E. Which pair of molecules does not represent isomers?
C
F. Which pair of molecules are identical? D
CH2OH
OH CH3 HOH2C H CH3 H HO CH2OH
OH H HOH2C CH3 CH3 H HO CH2OH CH2OH H HO CH2OH
G.
Which of the following has the molecules in order of increasing nucleophilicity? A. ACBDE B. CADBE H2O OHOO OH C. BADEC D. CDAEB E A B C D E. ADCEB
H.
What is the correct stereochemical assignment for each of the following alkenes?
H CH2OH H
HOH2C H HOH2C
CH2OH H
Cl
A
A. B. C D. E.
B
C
D
A = E; B = Z; C = E; D = Z A = Z; B = E; C = E; D = E A = E; B = E; C = Z; D = Z A = E; B = E; C = Z; D = E A = E; B = E; C = E; D = E Page 2
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Chem. 121
Exam II (3/21/07)
Name_____________________________________
I.
Which of the labeled hydrogens in the compound below is most readily abstracted under conditions of E2 elimination? Hb A. Ha Hc Ha B. Hb H3C CH2 C. Hc H D. Hd He d Br E. He
J.
Predict the two most likely mechanisms for the reaction of 3-iodopentane with sodium ethoxide in DMSO (an aprotic solvent). A. SN2 and SN1 B. E1 and E2 C. SN2 and E2 D. E1 and SN1 E. E2 and SN1
Page 3
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Chem. 121
2.
Exam II (3/21/07)
Name_____________________________________
Stereochemistry
A.
(2 pts) How many stereogenic centers does the following compound have?
B.
(6 pts) Label all the stereogenic center(s) in each compound. OH
OH OH
OH
OH
OH
O
C.
The specific rotation of the commercial drug l-Meradicin is [α] = -10˚*ml*g-1*dm-1. For a newly synthesized sample of 0.1 g/ml l-Meradicin the measured α was -0.5˚ (1 dm cell). 1)
(3 pts) What is the ee of the newly synthesized drug? Show your calculations.
2)
(3 pts) What is the percentage of d- and of l-Meradicin in that sample?
Page 4
%
Chem. 121
Name_____________________________________
Understanding Organic Reactions A. (4 pts) Draw the mechanism for CH3I + HCl CH3Cl + HI.
B. (4 pts) Is the above reaction exothermic? What is ΔH˚? (use the table at the end of the exam)
C. Consider the following energy diagram for the overall reaction: (CH3)3CI
Energy
3.
Exam II (3/21/07)
water
(CH3)3COH + HI:
(CH3)3C+ + I+ (H3C)3C OH2 + I(H3C)3C OH + HI
(H3C)3C I
Reaction coordinate
1. (6 pts) Draw the structure of the transition state for each step and indicate its location on the energy diagram.
2.
(2 pts) If a catalyst lowers the second barrier to half its value, will the reaction rate increase? Explain.
Page 5
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Chem. 121
4.
Exam II (3/21/07)
Name_____________________________________
Substitution and Elimination Reactions A. (6 pts) Determine (and write) the mechanism of nucleophilic substitution for each reaction and draw the products, including stereochemistry. acetone
H
1)
Br
+ CN-
Br
+ CH3CH2O-
acetone
2)
3)
Br
ethanol + CH3CH2OH
B.
(4 pts) Draw detailed mechanisms for the following reaction.
C. D. E.
(3 pts) Name the mechanism for each reaction (E1, E2, SN1, or SN2). (2 pts) Which one of the elimination products is the major product? (2 pts) What is the stereochemistry of the substitution product? ethanol
Cl
O
+
+
+ HCl
F. (3 pts) Which of the following compounds (A and B) will eliminate HBr through E1 mechanism and which through E2? Draw the transition state(s) for each elimination reaction. Br
A
Br
B Page 6
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Chem. 121
Exam II (3/21/07)
Name_____________________________________
G. (4 pts) cis-4-methyl-1-bromocyclohexane in water reacts with the water to yield two alcohols. The same bromoalkane reacts with sodium hydroxide (NaOH) in DMSO ((CH3)2S=O) to yield only one of these alcohols. Draw the two reactions and name the two products.
H. The alkylbromide trans-2-methyl-1-bromocyclohexane reacts with potassium tert-butoxide in DMSO to yield only one product. 1) (2 pts) Draw this product.
2)
(6 pts) Table 1 give the reaction rates at various concentrations of reactants. What is the reaction mechanism? Write the rate equation.
Reaction Rate [s-1] 1.0 2.0 4.0
3)
R-X [M] 0.1 0.2 0.2
K+ -OC(CH3)3 [M] 0.5 0.5 1.0
(bonus 5 pts) Calculate the rate constant (k) for this reaction. Specify the units of this constant.
Page 7
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Chem. 121
5.
Exam II (3/21/07)
Name_____________________________________
Alcohols A. (4 pts) Give an IUPAC name for each alcohol. (CH3)2CHCH2CH2CH2OH
HO
B. (4 pts) Name each ether and epoxide:
O
O
Page 8
%
Chem. 121
Exam II (3/21/07)
Name_____________________________________
Page 9
%
Organic I
Spring 2007
3/21/07
Exam II Last Name ______________________ First Name ______________________ (PRINTED) (PRINTED) UI ID #
_________________________________
Write your name on each page. Please read each question carefully before answering. Answer the questions in ink in the spaces provided inside. If you make changes as you go, please make sure your final answer is clearly indicated. You have 90 min. Good Luck! _______________________________________________________________________
Grading: Q.#
Score
(Max)
1.
__________ (30 pts)
2.
__________ (14 pts)
3.
__________ (16 pts)
4.
__________ (32 pts)
5.
__________ (8 pts)
Total:__________ (100 pts)
Chem. 121
Exam II (3/21/07)
Name_____________________________________
1.
(3 pts each) Please circle one answer for each question.
A.
How many chiral centers are present in the following compound? A. 0 B. 1 C. 2 D. 3 E. 4
B.
Designate the following stereogenic centers as R or S (from left to right). A. R,S. B. S,S. C. S,R. D. R,R. E. None of the above. CH3 A H HO
Consider the following pairs of molecules:
C. Which pair of molecules represents a pair of enantiomers?
B
D. Which pair of molecules represents constitutional isomers? E. Which pair of molecules does not represent isomers?
C
F. Which pair of molecules are identical? D
CH2OH
OH CH3 HOH2C H CH3 H HO CH2OH
OH H HOH2C CH3 CH3 H HO CH2OH CH2OH H HO CH2OH
G.
Which of the following has the molecules in order of increasing nucleophilicity? A. ACBDE B. CADBE H2O OHOO OH C. BADEC D. CDAEB E A B C D E. ADCEB
H.
What is the correct stereochemical assignment for each of the following alkenes?
H CH2OH H
HOH2C H HOH2C
CH2OH H
Cl
A
A. B. C D. E.
B
C
D
A = E; B = Z; C = E; D = Z A = Z; B = E; C = E; D = E A = E; B = E; C = Z; D = Z A = E; B = E; C = Z; D = E A = E; B = E; C = E; D = E Page 2
%
Chem. 121
Exam II (3/21/07)
Name_____________________________________
I.
Which of the labeled hydrogens in the compound below is most readily abstracted under conditions of E2 elimination? Hb A. Ha Hc Ha B. Hb H3C CH2 C. Hc H D. Hd He d Br E. He
J.
Predict the two most likely mechanisms for the reaction of 3-iodopentane with sodium ethoxide in DMSO (an aprotic solvent). A. SN2 and SN1 B. E1 and E2 C. SN2 and E2 D. E1 and SN1 E. E2 and SN1
Page 3
%
Chem. 121
2.
Exam II (3/21/07)
Name_____________________________________
Stereochemistry
A.
(2 pts) How many stereogenic centers does the following compound have?
B.
(6 pts) Label all the stereogenic center(s) in each compound. OH
OH OH
OH
OH
OH
O
C.
The specific rotation of the commercial drug l-Meradicin is [α] = -10˚*ml*g-1*dm-1. For a newly synthesized sample of 0.1 g/ml l-Meradicin the measured α was -0.5˚ (1 dm cell). 1)
(3 pts) What is the ee of the newly synthesized drug? Show your calculations.
2)
(3 pts) What is the percentage of d- and of l-Meradicin in that sample?
Page 4
%
Chem. 121
Name_____________________________________
Understanding Organic Reactions A. (4 pts) Draw the mechanism for CH3I + HCl CH3Cl + HI.
B. (4 pts) Is the above reaction exothermic? What is ΔH˚? (use the table at the end of the exam)
C. Consider the following energy diagram for the overall reaction: (CH3)3CI
Energy
3.
Exam II (3/21/07)
water
(CH3)3COH + HI:
(CH3)3C+ + I+ (H3C)3C OH2 + I(H3C)3C OH + HI
(H3C)3C I
Reaction coordinate
1. (6 pts) Draw the structure of the transition state for each step and indicate its location on the energy diagram.
2.
(2 pts) If a catalyst lowers the second barrier to half its value, will the reaction rate increase? Explain.
Page 5
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Chem. 121
4.
Exam II (3/21/07)
Name_____________________________________
Substitution and Elimination Reactions A. (6 pts) Determine (and write) the mechanism of nucleophilic substitution for each reaction and draw the products, including stereochemistry. acetone
H
1)
Br
+ CN-
Br
+ CH3CH2O-
acetone
2)
3)
Br
ethanol + CH3CH2OH
B.
(4 pts) Draw detailed mechanisms for the following reaction.
C. D. E.
(3 pts) Name the mechanism for each reaction (E1, E2, SN1, or SN2). (2 pts) Which one of the elimination products is the major product? (2 pts) What is the stereochemistry of the substitution product? ethanol
Cl
O
+
+
+ HCl
F. (3 pts) Which of the following compounds (A and B) will eliminate HBr through E1 mechanism and which through E2? Draw the transition state(s) for each elimination reaction. Br
A
Br
B Page 6
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Chem. 121
Exam II (3/21/07)
Name_____________________________________
G. (4 pts) cis-4-methyl-1-bromocyclohexane in water reacts with the water to yield two alcohols. The same bromoalkane reacts with sodium hydroxide (NaOH) in DMSO ((CH3)2S=O) to yield only one of these alcohols. Draw the two reactions and name the two products.
H. The alkylbromide trans-2-methyl-1-bromocyclohexane reacts with potassium tert-butoxide in DMSO to yield only one product. 1) (2 pts) Draw this product.
2)
(6 pts) Table 1 give the reaction rates at various concentrations of reactants. What is the reaction mechanism? Write the rate equation.
Reaction Rate [s-1] 1.0 2.0 4.0
3)
R-X [M] 0.1 0.2 0.2
K+ -OC(CH3)3 [M] 0.5 0.5 1.0
(bonus 5 pts) Calculate the rate constant (k) for this reaction. Specify the units of this constant.
Page 7
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Chem. 121
5.
Exam II (3/21/07)
Name_____________________________________
Alcohols A. (4 pts) Give an IUPAC name for each alcohol. (CH3)2CHCH2CH2CH2OH
HO
B. (4 pts) Name each ether and epoxide:
O
O
Page 8
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Chem. 121
Exam II (3/21/07)
Name_____________________________________
Page 9
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