1
Name
Answer Key
CHEM 247
Exam 3
10 November, 2008
University Honor Code Acknowledgment
I have neither given nor received assistance during this exam.
Your Signature
Question 1
(20)
Question 6
(10)
Question 2
(10)
Question 7
(15)
Question 3
(20)
Question 8
(10)
Question 4
(10)
Question 9
_______ (20)
Question 5
______ (10)
Total
Points (out of 125)
2
1. a) The following compound contains 2 types of acidic α-hydrogens. Draw structures of
i) the thermodynamic enolate and ii) the kinetic enolate derived from this ketone. (10 pts)
O
Thermodynamic enolate:
O-
Kinetic Enolate:
O-
3
b) Below are results of reactions of an α,β-unsaturated ketone with various
organometallic species (10 pts).
O
H3C
1) CH3M in THF, O oC
+
2) H2O
Reaction
1
Organometallic Reagent
CH3-Li
O
OH
CH3
1,2-addition
1,4-addition
1,2-addition
1,4-addition
>99
<1
2
CH3-MgBr
79
21
3
(CH 3) 2-CuLi
2
98
A) Which of the reactions 1-3, if any, are under kinetic control?
1 and 2
B) Which organometallic reagent is the weakest base?
(CH3)2-CuLi
4
2a). When levulinic acid 1 was reduced with NaBH4 a single product, compound 2
(C5H8O2), was isolated after aqueous work-up. Compound 2 lacked a hydroxyl
absorption in its infrared spectrum. What is the structure of 2? (5 pts)
O
O
O
1) NaBH4
OH
2
2) H3O+
O
1
b) Over time compound 3 rearranges to a more stable isomer 4. Acid hydrolysis of both
3 and 4 gives the amino alcohol 5. Suggest a reasonable structure for 4. (5 pts)
O
NH2
O
O
N
H
OH
4
3
HCl, H2O, !
HCl, H2O, !
NH2
OH
5
5
3. Synthesis (20 pts). Show all reagents and intermediates needed to convert compounds
on the left to ones on the right. You may use carbon sources with 2 or less carbons.
a)
O
O
O
O
O
HCN
O
H3O+
C
N
OH
heat
O
1) NaBH4
2)H3O+
O
O
b)
O
OH
H
O
H3C
O
1) LDA, THF
H2C
H
O
O
H
+
_
H
_
1) THF
OH
O
H
H2C
H
2) H2O
H+ or OH-, heat
OH
O
NaBH4, MeoH
H
6
4. a) Estradiol 4 exists primarily as the enol tautomer. Draw the enol form of 4. (5 pts)
OH
OH
HO
O
Estradiol 4
Keto Form
Estradiol 4
Enol Form
b) Why is estradiol’s enol tautomer favored over its keto tautomer? (5 pts)
It’s aromatic
7
5. Provide a stepwise mechanism for 1 of the following 2 reactions. Show all the
intermediates and the proper arrows for electron flow. ONLY DO ONE (10 pts).
O
O
H 3C
OH_
H 3C
H2 O
or
O
O
OH_
CH3
H2 O
H 3C
O
H 3C
O
O
H 3C
H O
H
H
CH3
H 3C
H
H
OH_
OH_
H O
H
OH_
OH_
H
O
Retro-Aldol
O
H 3C
CH3
H2 O
O
H 3C
H2 O
CH3
O
H
O
CH3
Aldol
O
O
Dehydration
HO
CH3
CH3
8
6. (10 points) Draw the products from reaction of carvone with the following reagents.
O
Carvone
a. HOCH2CH2OH, HCl
b. 1) LiAlH4 2) H3O+
OH
O
O
b.
d.1) C6H5MgBr 2) H3O+
c) CH3NH2
O
OH
NHMe
e) 2 Equivalents of H2/Pd
O
9
7. (15 pts) Acid-catalyzed hydrolysis of the 2 acetals shown below 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 (15 pts).
H
O
H
HCl (cat)
Reaction is complete in 1 hour at 20 oC
+ H2O
O
THF
H
O
H
HCl (cat)
+
O
O
THF
O
H
O
O
Reaction is complete in 24 hours at 60 oC
H2O
H+
O
H
+ H
O H
+
O
OH
H
+
O
OH
This carbocation is
stabilized
by resonance
H
O
O
H+
O
H
+ H
O H
+
O
OH
This carbocation is NOT
stabilized by resonance
10
8. Ketone 1 reacts with acetic anhydride and pyridine to give 2. However, unsubstituted
ketone 3 does not react under the same conditions. Given this information, show a
reasonable mechanism for conversion of 1 to 2. Remember that pyridine is a base (10 pts)
O
OH
O
OH
O
pyridine
O
O
1
O
2
O
O
O
pyridine
No Reaction
O
3
First, Nucleopilic Acyl Substitution to form an ester.
Second, an intramolecular Claisen condensation.
O
OH
O
O
O
O
pyridine
O
O
O
O
O
H
O
N
O
O
-
H
N+
-
O
O
O
OH
O
O
11
9. Each multiple choice part a)-d) is worth 5 points. Circle the best answer. (20 pts)
a) Circle the best value for the following reaction's equilibrium constant.
O
_
O
Keq
O
O
+
+
OH
Keq= 10-40
b)
10-15
1
O
C)
1015
10
Circle the compound with the most nucleophilic double bond.
H3C
CH3
NMe2
NH
CH3
H3C
CH3
H3C
H3C
CH3
Circle the compound that is most easily hydrated.
O
H
H3C
H3C
O
H
H3C
CH3
O
NH2
d) Circle the organic product that is expected from this reaction sequence.
O
Br
N
H
(C)
O
(B)
H3O+
O
OH
(A)
_
O
(D)
O
1040