1. 13.20 Infrared Spectroscopy
Gives information about the functional groups in a molecule 1

2. Infrared Spectroscopy
region of infrared that is most useful lies between m ( cm-1)
depends on transitions between vibrational energy states
stretching
bending 2

3. Stretching Vibrations of a CH2 Group
Symmetric
Antisymmetric 2

4. Bending Vibrations of a CH2 Group
In plane
In plane 2

5. Bending Vibrations of a CH2 Group
Out of plane
Out of plane 2

6. Figure 13.31: Infrared Spectrum of Hexane
bending
C—H stretching
bending
bending
CH3CH2CH2CH2CH2CH3
2000
3500
3000
2500
1000
1500
500
Wave number, cm-1
Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved. 8

7. Figure 13.32: Infrared Spectrum of 1-Hexene
C=C
H—C
C=C—H
H2C=C
H2C=CHCH2CH2CH2CH3
2000
3500
3000
2500
1000
1500
500
Wave number, cm-1
Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved. 8

8. Table 13.4 (p 583) Infrared Absorption Frequencies
Structural unit Frequency, cm-1
Stretching vibrations (single bonds)
sp C—H
sp2 C—H
sp3 C—H
sp2 C—O 1200
sp3 C—O 8

9. Table 13.4 (p 583) Infrared Absorption Frequencies
Structural unit Frequency, cm-1
Stretching vibrations (multiple bonds) C —C C— —C N 8

10. Table 13.4 (p 583) Infrared Absorption Frequencies
Structural unit Frequency, cm-1
Stretching vibrations (carbonyl groups)
Aldehydes and ketones
Carboxylic acids
Acid anhydrides and
Esters
Amides 8

11. Table 13.4 (p 583) Infrared Absorption Frequencies
Structural unit Frequency, cm-1
Bending vibrations of alkenes
CH2
RCH
CH2
R2C
890
CHR'
cis-RCH
CHR'
trans-RCH
CHR'
R2C 8

12. Table 13.4 (p 583) Infrared Absorption Frequencies
Structural unit Frequency, cm-1
Bending vibrations of derivatives of benzene
Monosubstituted and
Ortho-disubstituted
Meta-disubstituted and
Para-disubstituted 8

13. Figure 13.33: Infrared Spectrum of tert-butylbenzene
Ar—H
C6H5C(CH3)3
H—C
Monsubstituted benzene
2000
3500
3000
2500
1000
1500
500
Wave number, cm-1
Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved. 8

14. Table 13.4 (p 583) Infrared Absorption Frequencies
Structural unit Frequency, cm-1
Stretching vibrations (single bonds)
O—H (alcohols)
O—H (carboxylic acids)
N—H 8

15. Figure 13.34: Infrared Spectrum of 2-Hexanol
H—C
O—H OH
CH3CH2CH2CH2CHCH3
2000
3500
3000
2500
1000
1500
500
Wave number, cm-1
Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved. 8

16. Figure 13.35: Infrared Spectrum of 2-Hexanone
CH3CH2CH2CH2CCH3
H—C
C=O
2000
3500
3000
2500
1000
1500
500
Wave number, cm-1
Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved. 8