Spectroscopy Worksheet Page 2
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1
2CHEM 8L
IR Problems
Exercises
451
1. How could you use IR spectroscopy to distinguish between the following pairs of isomers:
a) CH
CH
OH and CH
OCH
b) cyclohexane and 1-hexene
3
2
3
3
Infrared Spectroscopy
c) CH
CH
CO
H and HOCH
CH
CHO (an aldehyde)
3
2
2
2
2
12.27 How might you use IR spectroscopy to distinguish among the three isomers
1-butyne, 1,3-butadiene, and 2-butyne?
2. What functional groups might the following molecules contain?
12.28 Would you expect two enantiomers such as (R)-2-bromobutane and
-1
a) A compound with a strong absorption at 1710 cm
(S)-2-bromobutane to have identical or different IR spectra? Explain.
-1
b) A compound with a strong absorption at 1540 cm
-1
-1
c) A compound with strong absorptions at 1720 cm
and 2500-3100 cm
12.29 Would you expect two diastereomers such as meso-2,3-dibromobutane and
(2R,3R)-dibromobutane to have identical or different IR spectra? Explain.
12.30 Propose structures for compounds that meet the following descriptions:
3. Acetone (CH
COCH
) and 2-propen-1-ol (H
C=CHCH
OH) are isomers. How could you
3
3
2
2
1
(a) C
H
, with IR absorptions at 3300 and 2150 cm
distinguish them by IR spectroscopy?
5
8
1
(b) C
H
O, with a strong IR absorption at 3400 cm
4
8
1
(c) C
H
O, with a strong IR absorption at 1715 cm
4
8
1
(d) C
H
, with IR absorptions at 1600 and 1500 cm
4. Propose structures for compounds that meet the following descriptions:
8
10
-1
a) C
H
, with IR absorptions at 3300 and 2150 cm
12.31 How could you use infrared spectroscopy to distinguish between the follow-
5
8
-1
b) C
H
O, with a strong IR absorption at 3400 cm
ing pairs of isomers?
4
8
(a) HC q CCH
NH
and CH
CH
C q N
2
2
3
2
(b) CH
COCH
and CH
CH
CHO
3
3
3
2
5. Two IR spectra are below. One is for cyclohexane and the other for cyclohexene. Identify
12.32 Two infrared spectra are shown. One is the spectrum of cyclohexane, and the
them and explain your answer.
other is the spectrum of cyclohexene. Identify them, and explain your answer.
(a)
100
80
60
40
20
0
4000
3500
3000
2500
2000
1500
1000
500
–1
Wavenumber (cm
)
(b)
100
80
60
40
20
0
4000
3500
3000
2500
2000
1500
1000
500
–1
Wavenumber (cm
)
th
IR problems reproduced from McMurry, J. “Organic Chemistry, 8
edition.”
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