1. INFRARED SPECTROSCOPY
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2. WWU Chemistry

3. Infrared Spectrometer
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4. Molecular vibrations IR-Tutor available in CB 280 is great!
Basically two types
stretching vibrations
bending vibrations
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5. IR TUTOR Select Chemistry Applications icon
Select Structure Drawing icon
Select Spectroscopy icon
Select IR Tutor icon
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6. Typical Infrared Absorption Regions
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7. C-H stretching region Alkanes C-H sp3 stretch < 3000 cm-1
Alkenes C-H sp2 stretch > 3000 cm-1
Alkynes C-H sp stretch ~ 3300 cm-1

8. C-H bending region CH2 bending ~ 1460 cm-1
CH3 bending (asym) appears near the same value
CH3 bending (sym) ~ 1380 cm-1

9. Hexane
CH3 bend
CH2 bend
C-H stretch
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10. How do you think the infrared
spectrum of polyethylene would
differ from the spectrum of
hexane?????

11. cm-1
The C=C is found at about 1650 cm-1. Monomers would be expected to show the C=C bond, but in polymers the double bond will be absent, unless there is a benzene ring.
The double bonds in a benzene ring are found in the range of about 1600 to 1450 cm-1
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12. 1-Hexene sp2 C-H C=C stretch out of plane bendings (oops) sp3
C-H stretch
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13. Toluene
sp2
C-H
sp3
C-H
aromatic
C=C
aromatic oops
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14. O-H stretching region
O-H cm-1 (alcohol). Common polymers with O-H: cellulose and PVA
O-H cm-1 (acid, broad and ugly). Dicarboxylic acids are monomers. When the carboxylic acid is polymerized with an diol, you get an polyester.

15. Cyclohexanol bending O-H stretch C-O stretch sp3 C-H stretch
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16. Butanoic Acid
O-H stretch
C=O stretch
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17. 2250 cm-1 C≡N 2250 cm-1 The only common polymers with this functional
group: polyacrylonitrile and ABS
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18. Propanenitrile
sp3 C-H
C≡N
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19. N-H stretching region 3300 - 3400 cm-1
–NH2 Primary amines give a pair of peaks. You don’t see primary amines in polymers.
-NH Secondary amines give a single peak
The N-H in polyamides and polyurethanes show a very prominent singlet peak!

20. 1-Butanamine N-H bend CH2 N-H CH3 stretch bend doublet sp3 C-H stretch
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21. 3-Methylbenzenamine sp2 & sp3 C-H N-H stretch Aromatic C=C N-H bend
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22. N-Ethylbenzenamine N-H sp2 & sp3 C-H stretch Aromatic C=C
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23. cm-1
This is the carbonyl region!! All bands are very strong!!
The following polymers would be expected to show prominent C=O peaks:
Polyesters
Acrylics
Polyamides and polyurethanes
Poly ether ketone (PEEK)
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24. C=O Stretching in monomers and polymers
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25. 2-Butanone
sp3 C-H
stretch
C=O stretch
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26. 4-Methyl-2-pentanone C-H < 3000, C=O @ 1715 cm-1
C-H stretch
C=O stretch
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27. Ethyl Butanoate
C-O stretch
sp3 C-H
C=O stretch
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28. Butanoic Acid
O-H stretch
C=O stretch
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29. Propanamide
sp3 C-H
C=O and
N-H stretch
(pair)
N-H bend
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30. Conjugation of C=O with C=C
Conjugation of a carbonyl with a C=C bond shifts values to lower frequencies
For ketones and esters, subtract about 30 cm-1 for conjugation with C=O
Conjugated ketone = 1690 to 1680 cm-1
Conjugated ester = 1710 to 1700 cm-1
C=C becomes quite strong!!
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31. 4-Methyl-3-penten-2-one
C-H stretch
C=O
stretch
C=C
stretch
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32. Acetophenone
C-H stretch
aromatic C=C
conj C=O
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33. C-X stretching region
C-Cl 785 to 540 cm-1, often hard to find amongst the fingerprint bands!!
C-Br and C-I appear outside the useful range of infrared spectroscopy.
C-F can be found easily, but aren’t that common - exception! polytetrafluoroethylene
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34. Carbon Tetrachloride
no C-H!
C-Cl stretch
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