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CHEM 241 (Davis) Organic Chemistry II
Final Exam
Friday December 14, 2007
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(Last, First)
DISCUSSION SECTION #
_____
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• Please put your discussion section number in the space provided.
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2
Name
CHEM 241
Final Exam
14 December, 2007
University Honor Code Acknowledgment
I have neither given nor received assistance during this exam.
Your Signature
Total
Part 1
(100)
Part 2
(40)
Part 3
(60)
Points (out of 200)
3
PART 1-Multiple choice with 20 questions at 5 points each (100 pts).
1.
Circle the best value for the pKA of methanol (CH3OH).
-10
2.
-5
0
16
40
60
Circle the best value for the pKA of acetone (CH3COCH3).
-10
3.
5
0
10
20
40
60
Circle the best value for the following equilibrium constant.
O
_
O
Keq
O
O
+
+
_
OH
10-15
4.
O
1
1015
Circle the number of different types of hydrogen atoms in the following compound.
H3C
O
O
O
0
5.
15
2
CH3
O
4
5
6
9
Circle the strongest base.
_
_
OH
O
N
_
N
H
N
4
6.
PAGE 2
Circle the compound that is the best Lewis acid.
O
O
H
O O
OH
O
N
C
C
O
N
H
H
B
Cl
7.
Circle the best value for the strength of a hydrogen bond X-H......Y.
0.01-0.1
8.
3-8
3-8
80-100
1000-1200
O
O
(kcal/mol)
O
O
OH
H
S
O
Circle the most reactive carbocation.
CH3
F3C + CF3
11.
(kcal/mol)
Circle the compound that is reduced slowest by LiAlH4.
O
10.
1000-1200
Circle the best value for the strength of a C-C single bond.
0.01-0.1
9.
80-100
O
CH3
F3C
+
H3C + CH3
CH3
CH3
CH3
H3C + CH3
Circle the compound that reacts fastest with Br2.
O
H3C
CH3
H3C
NMe2
NH
CH3
H3C
CH3
H3C
CH3
H
5
12.
Circle the compound that reacts fastest with NaBH4.
O
H
H3C
13.
O
H
H3C
O
CH3
H3C
NH2
Circle the compound that can form the most hydrogen bonds with water.
O
O
O
H3C
H2N
H
CH3
H
CH3
CH3
14. Circle the conformation that can react with base to give an epoxide.
OH
OH
Br
H
H
Br
CH3
H3C
Br
H
CH3
H
CH3
H
CH3
CH3
Br
OH
HO
H
CH3
H
H
15. Circle the name of the author of our Organic chemistry text.
Breeze
Bobwhite
Bruice
Biochem
16. Circle the most acidic H in the following compound.
O
O
H
O
H 3C
CH3
H
17. Circle the least electrophilic carbonyl in the compound below.
O
H2N
O
O
H
CH3
Baltic
6
18. Circle the compound with the most acidic hydrogen
O
O
O
O
H
H
O
O
O
19. Circle the compound that has the highest enol content.
O
O
O
O
H
H
O
O
O
20. If exactly one equivalent of OH- is added to the cyclobutane 1, a mono-carboxylic acid is formed.
Draw the structure of the expected hydrolysis product.
O
OMe
Cl
O
O
NH2
O
O
O
1
OHTHF
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Part 2-Short Answer
21. Reaction of ethanol with H2CrO4 in H2O gives acetic acid while reaction of ethanol with pyridinium
chlorochromate (PCC) in CH2Cl2 gives acetaldehyde. Both H2CrO4 and PCC are Cr (VI) oxidants.
Clearly explain why the product obtained upon oxidation of ethanol by Cr (VI) is so dependant on the
solvent. (10 pts)
OH
H2CrO4
H2O
O
PCC
OH
OH
CH2Cl 2
O
H
8
22. As shown below, HCN reacts with an α,β-unsaturated aldehyde to give primarily the 1,4conjugate addition product, rather than the 1,2-addition product.
H
+
H-C N
NC
H
H
+
O
O
NC
1,4-addition
major product
OH
1,2-addition
minor product
Briefly explain, then, why reaction of HCN and benzaldehyde gives only cyanohydrin (the 1,2-addition
product) and none of the 1,4-addition product aldehyde (10 pts).
H + H-C N
O
H
HO CN
1,2-addition
Only product
+
H
CN
O
No 1,4-addition
product observed
9
23.The acid-catalyzed hydrolysis of the following 2 acetals occurs at much different rates. Draw
structures of reaction intermediates and provide a brief explanation to illustrate why these 2 acetals
undergo hydrolysis at such different rates (10 pts).
H
O
O
Reaction is complete in 1 hour at 20 oC
+ H2O
THF
H
O
O
H
p-TsOH
O
H
p-TsOH
+
H2O
THF
O
Reaction is complete in 24 hours at 60 oC
10
24. Treatment of the 2 compounds with Ag+ gives the respective benzyl cations. Circle the more
stable benzyl cation. Use resonance forms to illustrate and justify your answer. (10 pts)
Cl
+
+
Ag+
AgCl
+
OMe
OMe
Cl
+
OMe
+
Ag+
OMe
AgCl
+
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Part 3. Mechanism with 2 questions at 20 points each (60 pts).
25.
Provide a stepwise mechanism for the following reaction:
O
O
OH
+
Cl
S
O
Cl
Cl
+
SO2
+
HCl
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26. Provide a stepwise mechanism for the following reaction:
CH3
+
H3C
Cl
AlCl3
N
N
H
H
CH3
CH3
CH3
+
HCl
13
27. Show a step-wise mechanism for the following base-catalyzed rearrangement:
OH
OHO
H
O
OH
H2O
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BLANK PAGE FOR SCRATCH WORK