CHEM460 EXAM #3 Name .
Fall, 2017
Professor Sasaki
100 points TOTAL Good Luck!
Note: Only answers in the box will be graded.
1. (25) Consider 1 H-NMR of the following compounds, and answer the questions.
CH
3
O O
H
3
C
O
O
CH
3
O O
CH
3
(a) Which compound(s) has an A4 spin system?
O O
O
(b) Which compound(s) has a pair of diastereotopic protons? Write the structure of the compound(s), and show the location of diastereotopic protons.
(c) Which compound(s) has an AA'BB' or AA'XX' spin system? Write the structure of the compound(s), and label the protons with letters (A, A', X, etc).
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(d) For each compound, describe the 1 H-spin system by using the Pople notation (A, B,
C, M, X etc.
(i) (iii)
Cl
Cl
Cl
Cl
Cl Cl https://www.coursehero.com/file/36475791/Chem460-2017-Exam3pdf/
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Chem460 page 2
2. (25) For each problem below, compare the magnitude of the coupling constants indicated. Provide a brief (1-2 sentence) explanation for the expected difference in magnitude for J .
(a)
Ha Hc
Hb CH
3
2 J ab
vs 3 J ac
vs 3 J bc
> >
Smaller J Larger J
(b)
Hb
3 J ab
vs 3 J ac
Hc
Ha
>
Larger J
(c)
Smaller J
Ha
4 J ab
vs 4 J ac
Hb
Hc
>
(d)
Smaller J Larger J This study resource was shared via CourseHero.com
>
Smaller J Larger J https://www.coursehero.com/file/36475791/Chem460-2017-Exam3pdf/
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Chem460 page 3
3. (25) (a) Consider the two methyl decalin isomers, A and B . Circle the isomer whose methyl group has the larger linewidth. Provide your reasoning.
CH
3
CH
3
A B
(b) Analyze the following multiplet by using the Inverted Splitting Tree Generation and determine J values.
15 10 5 0 -5 -10 -15 Hz
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Chem460 page 4
4. (30) (a) The 1 H- and 13 C-NMR of an unknown compound (C
6
H
10
O) are shown in the next page. Determine the structure of this compound. Be sure to show the basis for your conclusions.
C1
C2
C3
C4
C5
C6
H2
H4
H3
H1
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(b) The following splitting pattern may represent the 2 protons of an AB system or the X proton of an A
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Chem460 page 5
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CHEM460 page 6
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