CH Bocknack 310N Spring 2007 Midterm Exam #1 Answer Key Part I All answers to questions on this page must be submitted on the bubble sheet, using a #2 pencil. Only answers submitted on the bubble sheet will be graded!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
In Questions 1 through 3, a spectrum (IR, H NMR, or C NMR) is shown. Near each spectrum, four structures are given. Pick the structure that produced the spectrum, and indicate your choice on the answer sheet. 1. (10 points) What compound produced the IR spectrum given below? (+5 awarded if choice A was picked) H3C O C. A.
1 13
OH
B. O
1
H
D.
O
2. (10 points) What compound produced the H NMR spectrum given below? Please note that the multiplicity of each signal (i.e. singlet, doublet, triplet, etc.) is not given. You don't need to know this information to answer this question!
6H
2H 1H
1H
A.
B.
13
C.
D.
3. (10 points) What compound produced the in this spectrum.
C NMR spectrum given below? There are only 4 signals
CH3 CH3 A. C.
H3C CH3
CH3 B.
A. Polar molecule B. Nonpolar molecule
CH2CH3 D. CH3
2
Bocknack CH 310N Spring 2007 Midterm Exam #1 Answer Key Part I All answers to questions on this page must be submitted on the bubble sheet, using a #2 pencil. Only answers submitted on the bubble sheet will be graded!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
In Questions 4 through 8, you need to predict the number of signals that would be expected to appear in 1 the H NMR spectrum of each compound shown, ignoring spin-spin splitting. You should assume that each set of nonequivalent protons produces one signal, but don't worry about whether each signal is a singlet, a doublet, a triplet, etc. Indicate your choice on the answer sheet (Each type of nonequivalent proton is indicated with a different color in the structures below) 4. (5 points) How many signals would appear in the H NMR spectrum?
1
H H H
H H
H H
A. B.
1 2
C. D.
3 4
E. F.
5 6
G. H.
7 8
I. J.
9 10
H H
H H
H
1
5. (5 points) How many signals would appear in the H NMR spectrum?
H H
H H
H H
A. B.
1 2
C. D.
3 4
E. F.
5 6
G. H.
7 8
I. J.
9 10
H3C
H H
H
1
6. (5 points) How many signals would appear in the H NMR spectrum? (diastereotopic) H H H A. 1 C. 3 E. 5 B. 2 D. 4 F. 6 H H
G. H.
7 8
I. J.
9 10
H
H
H H
H
(+2 awarded if choice E was picked)
1
7. (5 points) How many signals would appear in the H NMR spectrum?
H3C H3C
O
CH3
A. B.
1 2
C. D.
3 4
E. F.
5 6
G. H.
7 8
I. J.
9 10
CH3 H C CH3 3
1
8. (5 points) How many signals would appear in the H NMR spectrum? (diastereotopic) A. 1 C. 3 E. 5 H H H B. 2 D. 4 F. 6 H
G. H.
7 8
I. J.
9 10
H H H H H OH
(+2 awarded if choice E was picked)
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Bocknack CH 310N Spring 2007 Midterm Exam #1 Answer Key Part I All answers to questions on this page must be submitted on the bubble sheet, using a #2 pencil. Only answers submitted on the bubble sheet will be graded!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
In Questions 9 through 13, determine whether the circled protons are homotopic, enantiotopic, diastereotopic, or constitutionally nonequivalent (i.e., a "substitution test" would give constitutional isomers). Indicate your choice on the answer sheet. 9. (5 points) What is the relationship between the circled protons?
H H H3 C CH3 Br H
C
A. B.
Homotopic Enantiotopic
C. D.
Diastereotopic Constitutionally nonequivalent
10. (5 points) What is the relationship between the circled protons?
H H
H H
H H
D
A. B.
Homotopic Enantiotopic
C. D.
Diastereotopic Constitutionally nonequivalent
H
H
Br
H
11. (5 points) What is the relationship between the circled protons?
H 3C H H H H H
B
A. B.
Homotopic Enantiotopic
C. D.
Diastereotopic Constitutionally nonequivalent
12. (5 points) What is the relationship between the circled protons?
H H CH3 H H H H CH3 H H
A
A. B.
Homotopic Enantiotopic
C. D.
Diastereotopic Constitutionally nonequivalent
13. (5 points) What is the relationship between the circled protons?
H3C CH2CH2 H C C H CH2CH2 H
C
A. B.
Homotopic Enantiotopic
C. D.
Diastereotopic Constitutionally nonequivalent
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Bocknack CH 310N Spring 2007 Midterm Exam #1 Answer Key Part I All answers to questions on this page must be submitted on the bubble sheet, using a #2 pencil. Only answers submitted on the bubble sheet will be graded!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
Questions 14 through 18 refer to the H NMR spectrum shown below. Each signal in this spectrum is marked with a letter. Match the letter corresponding to each signal with the proton(s) responsible for producing the signal. The structure of the molecule is provided below the spectrum The proton(s) you need to look at to answer each question are marked with the question number. Indicate your choice for each question on the answer sheet.
1
C
(6H, singlet)
B
(1H, singlet)
D
(6H, doublet)
A
(1H, septet)
14
H3 C H3 C
OH CH3
16
C A
14. (3 points) Which signal was produced by the set of protons marked 14? 15. (3 points) Which signal was produced by the proton marked 15? 16. (3 points) Which signal was produced by the proton marked 16?
15
H
CH3
17
B
D B
17. (3 points) Which signal was produced by the set of protons marked 17? 18. (3 points) Which signal in the H NMR spectrum above will disappear upon shaking the sample with D2O?
1
Note: The signal produced by hydroxyl proton will disappear upon D2O shake, due to chemical exchange. You received full credit for Q18 only if your answer to Q18 was the same as your answer to Q16!
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Bocknack CH 310N Spring 2007 Midterm Exam #1 Answer Key Part I All answers to questions on this page must be submitted on the bubble sheet, using a #2 pencil. Only answers submitted on the bubble sheet will be graded!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
Questions 19 through 23 refer to the H NMR spectrum shown below. Each signal in this spectrum is marked with a letter. Match the letter corresponding to each signal with the proton(s) responsible for producing the signal. The structure of the molecule is provided to the right of the spectrum The proton(s) you need to look at to answer each question are marked with the question number. Indicate your choice for each question on the answer sheet.
1
D C
(2H, triplet) (3H, singlet)
B
(2H, quartet)
E
(3H, triplet)
20
22
O
CH3CH2OCH2CH2CCH3 19
A
(2H, triplet)
21
23
E B A C D
19. (3 points) Which signal was produced by the set of protons marked 19? 20. (3 points) Which signal was produced by the set of protons marked 20? 21. (3 points) Which signal was produced by the set of protons marked 21? 22. (3 points) Which signal was produced by the set of protons marked 22? 23. (3 points) Which signal was produced by the set of protons marked 23?
Note: You received 1 point for Q21 if your Q21 choice = C and your Q22 choice = A You received 1 point for Q22 if your Q22 choice = A and your Q21 choice = C
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Bocknack CH 310N Spring 2007 Midterm Exam #1 Answer Key Part I All answers to questions on this page must be submitted on the bubble sheet, using a #2 pencil. Only answers submitted on the bubble sheet will be graded!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
Questions 24 through 28 refer to the C NMR spectrum shown below. Each signal in this spectrum is marked with a letter. Match the letter corresponding to each signal with the carbon atom responsible for producing the signal. The structure of the molecule is provided to the right of the spectrum The carbon atoms you need to look at to answer each question are marked with the question number. Indicate your choice for each question on the answer sheet.
13
A B D C E
24 28
25 27
O
26
H
CH3CH2CH2CH2OC
E C A B D
24. (3 points) Which signal was produced by the carbon atom marked 24? 25. (3 points) Which signal was produced by the carbon atom marked 25? 26. (3 points) Which signal was produced by the carbon atom marked 26? 27. (3 points) Which signal was produced by the carbon atom marked 27? 28. (3 points) Which signal was produced by the carbon atom marked 28?
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Bocknack CH 310N Spring 2007 Midterm Exam #1 Answer Key Part I All answers to questions on this page must be submitted on the bubble sheet, using a #2 pencil. Only answers submitted on the bubble sheet will be graded!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
Questions 29 through 33 are designed to test your understanding of spin-spin splitting. Indicate the multiplicity (i.e. total number of lines) that would be observed in the signal for each set of protons with marked a question number below. Pick from the "menu" of choices below to answer each question on this page. The molecule you need to look at is given below this menu. Indicate your choice for each question on the answer sheet.
A. B.
singlet doublet
C. D.
triplet quartet
E. F.
quintet sextet
G. H.
septet other multiplet not indicated
30
CH3CH2 O CH2
32
CH3 C O CH CH3
33
29
31
C D A B G
29. (5 points) What would be the appearance of the signal produced by the set of protons marked 29? 30. (5 points) What would be the appearance of the signal produced by the set of protons marked 30? 31. (5 points) What would be the appearance of the signal produced by the set of protons marked 31? 32. (5 points) What would be the appearance of the signal produced by the set of protons marked 32? 33. (5 points) What would be the appearance of the signal produced by the proton marked 33?
End Part I. Part II begins on Page 9...
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Bocknack CH 310N Spring 2007 Midterm Exam #1 Answer Key Part II Write your answers to all questions on this page in the space provided. If you use a pen, only blue or black ink is acceptable!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
34. (25 points) Compound X has molecular formula C6H12O. The IR, H NMR, and C NMR spectra for this compound are given below. Propose a structure for Compound X. Write your answer in the "answer box" at the bottom of this page. A correct structure is worth 15 points. To earn the remaining 10 points, you have to EXPLAIN why your proposed structure is consistent with the spectral data. Please limit your explanation to the space provided.
1 13
3H
(singlet)
(doublet) c
3H
a
3H
(triplet)
e What is the structure of X?
1H
(multiplet)
O C H3C
a
d,d' 1H
(multiplet)
d,d' b
b
CH
c
CH2CH3
e
CH3
1H
(multiplet)
Why is your proposed structure consistent with the spectral data? C6H12O has unsaturation number =1, so 1 pi bond or ring is present. 1 IR absorption near 1710 cm is consistent with the presence of a carbonyl group, which 13 accounts for the one unsaturation unit. The C NMR signal near 210 is also consistent with a carbonyl group 1 Since there is no H NMR signal near 910, the carbonyl compound is not an aldehyde. It must be a ketone. 1 The 3 separate 3H signals in the H NMR are due to 3 nonequivalent methyl groups. The one marked a above has no neighboring protons, and would yield a singlet. The one marked c above has one neighboring proton, and would yield a doublet. The one marked e above has two neighboring protons, and would yield a triplet. The proton marked b above would yield a multiplet, due to a total of 5 nonequivalent neighbors d and d' are diastereotopic, and therefore each produce Part II continues on Page 10... a 1H multiplet.
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Bocknack CH 310N Spring 2007 Midterm Exam #1 Answer Key Part II Write your answers to all questions on this page in the space provided. If you use a pen, only blue or black ink is acceptable!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
In Questions 35 through 39, predict the structure(s) of the major organic product(s) that will form when the organic starting material given is subjected to the indicated reaction conditions. If two different products are formed, draw both of them, one structure in each box. Be sure to show any stereochemistry clearly and unambiguously in each structure you draw. Remember, stereoisomers are different compounds, so you should draw both stereoisomers if they are both formed in the reaction. If only one product is formed in the reaction, draw it in one of the boxes, and fill the other box with the symbol "X". If no reaction occurs under the given conditions, fill both boxes with the symbol "X".
35. (12 points) CH3 CH3 CH2I2 Zn/Cu couple H (enantiomers) H + CH3
36. (12 points) OH H2O H2SO4 (cat.) (achiral) H OH +
O H
37. (12 points) O CH3 H C N pH = 1
pH is too low for cyanohydrin formation!!!
+
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Bocknack CH 310N Spring 2007 Midterm Exam #1 Answer Key Part II Write your answers to all questions on this page in the space provided. If you use a pen, only blue or black ink is acceptable!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
Please follow the instructions given at the top of Page 10.
38. (12 points)
I C CH3CH2 C
CH3
(CH3CH2CH2)2CuLi
CH3CH2CH2 C CH3CH2 C
CH3 + CH2CH3
CH2CH3
39. (12 points) HO O CH3CH2 1) CH3CH2Li 2) H3O+ CH3CH2 H CH2CH3 +
Page Total v
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Bocknack CH 310N Spring 2007 Midterm Exam #1 Answer Key Part II Write your answers to all questions on this page in the space provided. If you use a pen, only blue or black ink is acceptable!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
Questions 40 through 42 refer to the sequence of reactions shown below. One of the steps in this proposed synthesis will not work! Determine which step will not work, and explain why it will not work. Then, propose an alternative sequence of reactions that will allow the target compound to be synthesized from the indicated starting material.
Step A
Step B
H3C C H C
H
Br2, H2O
Br H3C
H CH3 OH H (racemic) (CH3CH2)2CuLi
CH3CH2 H3C
H CH3
CH3
(starting material)
OH H (racemic) (target compound)
40. (5 points) Which step in the synthesis shown above will not work to yield the product indicated? Circle your choice below.
Step A will not work
Step B will not work
41. (5 points) In the space below, explain briefly why the step you indicated above will not work as described. A correct explanation should require no more than a sentence or two!
The presence of the hydroxyl group (a proton donor) in the bromohydrin is incompatible with the Gilman reagent. The Gilman reagent will undergo protonolysis rather than the desired organometallic coupling reaction.
42. (15 points) Propose a sequence of reactions which will allow the target compound to be prepared from the indicated starting material. In addition to the starting material indicated, you may use any other organic and/or inorganic reagents necessary during the course of your synthesis. It is only necessary to show the overall transformations involved in your proposed syntheses please do not write curved arrow mechanisms in answering this question!!! Be sure that your final answer is indicated clearly and unambiguously. Points will be deducted if the graders cannot follow your reasoning, or if you do not follow these instructions!!!
H 3C C H C CH 3 H Br2 , H 2 O Br H3C H CH 3 H OH
(racemic)
mCPBA
NaOH (or other strong base) 1) CH 3 CH 2 MgX OR CH 3 CH 2 Li OR (CH 3 CH 2 )2 CuLi 2) H 3 O +
H H3C O
CH 3 H
CH 3 CH 2 H 3C
H CH 3 OH
(racemic)
H
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Bocknack CH 310N Spring 2007 Midterm Exam #1 Answer Key Part II Write your answers to all questions on this page in the space provided. If you use a pen, only blue or black ink is acceptable!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
Questions 43 and 44 refer to the overall transformation shown below:
H C CH3CH2 C
H
K
OC(CH3)3 CHCl3
Cl Cl
CH2CH3
H CH3CH2
H CH2CH3
43. (10 points) This reaction involves a carbene intermediate, which is formed via reaction of the tertbutoxide anion with chloroform. In the space below, propose a mechanism to account for formation of this carbene. Use curved arrows to show movement of electron pairs, and show structures of all important reaction intermediates.
Cl (CH3)3C O H C Cl Cl (CH3)3C O H C
Cl Cl Cl
Cl C Cl Cl
44. (10 points) Show how the carbene you formed in Question 43 reacts with the alkene starting material to yield the cyclopropane product. Once again, use curved arrows to show movement of electron pairs, and show structures of all important reaction intermediates.
Cl H CH3CH2
C C
Cl H CH2CH3
Cl
Cl
C
H CH3CH2
H CH2CH3
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Bocknack CH 310N Spring 2007 Midterm Exam #1 Answer Key Part II Write your answers to all questions on this page in the space provided. If you use a pen, only blue or black ink is acceptable!!! PLEASE READ EACH QUESTION VERY CAREFULLY!!!
45. (20 points) In lecture, we discussed the mechanism for the acid-catalyzed hydration of aldehydes and ketones. This reaction can also occur under basic conditions, as shown in the overall transformation below:
O H Na OH
HO OH H H2 O
In the space below, propose a mechanism for the base-catalyzed hydration of the aldehyde shown in the transformation above. Use curved arrows to show movement of electron pairs, and be sure to show structures of all important reaction intermediates.
O H
H OH
O H
OH
O
OH H
H O
OH H
END OF EXAM!!!
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