CHE 232 Organic Chemistry II
Exam 3
April 3, 2013
Name: KEY
Student number:
Before you begin this exam: First: You are allowed to have a simple model set at your
seat. Please put away all other materials. Second: Place your student identification on your
desk. A proctor will come around to check everyone’s ID. Third: Read through the entire
exam. Your goal, as always, is to score as many points as possible. Do not waste time on
problems that you can’t do if there are others that look easy. Fourth: READ EACH
QUESTION CAREFULLY. Be sure you answer the question that is asked. Fifth: This exam
must be turned in by 12:50 PM SHARP. There will be no extensions, so budget your time
carefully. Sixth: Efficiency and cleanliness count. Don’t propose reactions that require
excessively long times or difficult purifications if more efficient paths and reagents are
available.
1.
2. 3. 4. 5. 6. 7. 8. 12 points 30 points 12 points 16 points 5 points 10 points 5 points 10 points Total: 1 1. (12 points) For each of the equilibria shown below, circle the side that would be favored. O
O
+
CH3NH2
+
CH3OH
NHCH3
OCH3
The right side O
O
O
+
CH3OH
+
O
CH3CO2H
OCH3
The right side O
O
+
NaCl
+
NHCH3
CH3NH Na
Cl
The left side O
O
+
CH3S
+
OCH3
SCH3
CH3O
The left side 2. (30 points). For any SIX of the following, draw the expected major organic product. If you believe that two products (like ortho and para isomers) will be formed in significant amounts, show both. INDICATE WHICH PROBLEMS YOU WANT GRADED. a) Br
2. NaOH, H2O
3. HCl, H2O
grade? (Y/N) 1. KCN
CO2H
2 b) O
CO2H
OH
O
cat. H2SO4
grade? (Y/N) c) 1. NaOH, H2O
O
CH2OH
2. HCl, H2O
grade? (Y/N) O
CO2H
d) O
O
HOAc, Br2
grade? (Y/N) Br
e) O
O
O
CH3NH2
O
CO2H
CH3NH
grade? (Y/N) f) EtO2C
1. NaOH
Br
grade? (Y/N) 2 NaOEt
CO2Et
Br
2. HCl, H2O
CO2H
3 g) O
O
1. LDA, THF, -78 ˚C
2. CH3CH2CH2Br
grade? (Y/N) h) O
O
N
N
H
grade? (Y/N) Cl
Cl
N
N
(excess)
N
N
3. (12 points) Draw in arrow to the position of the most acidic proton on each of the following molecules. O
O
O
CH2CH3
CH3
CH2
CH2
HO2C
CH2
O
Ph
CH2
H
H
CH2
H
CH2
H
H
CH2
N
O
CH2
O
H
H
H
H
4 4. (16 points) Write in the reagents needed to carry out the transformations given below. If two (or more) steps are needed, be sure that you give both and designate the separate steps as 1) reagent A and 2) reagent B, etc. a) 1. NaOEt, C3H7Br
2. NaOH, H2O
3. HCl, H2O
O
CO2Et
O
b) O
DCC
H
N
H2N
H
N
CO2H
N
H
CO2CH3
O
CO2CH3
O
c) O
O
1. LDA, THF, -78˚C
2. EtBr
d) 1. SOCl2
O
2.
O
H2N
N
H
OH
5. (5 points) Offer a brief explanation as to why the hydrogen shown is not particularly acidic, even though it is adjacent to a carbonyl group. One sentence, and perhaps a drawing, will be plenty. Do not exceed the space provided. O
H
The resulting anion is not resonance stabilized. 5 6. (10 points) Alkyl lithium compounds are very strong bases, yet BuLi will NOT produce the kinetic enolate of a ketone, not of the ketone shown below and not of any other ketone. O
O
BuLi, THF, -78 ˚C
a) In ONE SENTENCE state why this reaction does not work. BuLi will react as a nucleophile and add to the carbonyl group. b) Draw the product that would actually form (after the obligatory acid workup step, of course). HO
7. (5 points) Attempts to make the dimethyl acetal of the keto ester shown below using methanol (as solvent) are unsuccessful. However, when ethanol is used instead of methanol, the desired product is formed. Draw the product that actually forms when methanol is used. O
OCH3
CH3O
OCH2CH3
CH3CH2O
CH3CH2OH
CH3OH
CO2CH2CH3
CO2CH2CH3
cat. TsOH
cat. TsOH
CO2CH2CH3
OCH3
CH3O
CO2CH3
(transesterification) 6 8. (10 points) Show how the diketone shown can be prepared from ethyl acetoacetate. You can use any inorganic reagents you need (including Ph3P) and any organic compounds of 4 carbons or less. Please show each step (reagents and product) in your synthesis. O
O
several steps
CO2Et
O
1.
CH3CH2Br + Mg
OH
H
CH3CH2MgBr
2. HCl, H2O
PBr3
O
+
Br
O
NaOEt
+
CO2Et
CO2Et
1. NaOH, H2O
2. HCl, H2O
O
7