1. The C=O stretching frequency
aldehydes and ketones

2. A summary of the principle infrared bands and their assignments
A summary of the principle infrared bands and their assignments. R is an aliphatic group.

3. Aliphatic Aldehyde
Figure IR-14. Butanal, neat liquid, thin film: CH3CH2CH2CHO

4. Aliphatic Ketone
Figure IR Hexene-2-one, neat liquid: CH2=CH2CH2CH2COCH3

5. The C=O stretching frequency
esters

6. A summary of the principle infrared bands and their assignments
A summary of the principle infrared bands and their assignments. R is an aliphatic group.

7. Aliphatic Ester
Figure IR-33. Methyl acetate in 0.1 mm NaCl cells: CH3CO2CH3

8. neat
CCl4

9. Aliphatic Ester
Figure IR-34. Vapor and liquid spectra of ethyl n-hexanoate: CH3CH2CH2CH2CH2CO2CH2CH3

10. The C=O stretching frequency
aliphatic acids

11. A summary of the principle infrared bands and their assignments
A summary of the principle infrared bands and their assignments. R is an aliphatic group.

12. Aliphatic Acid Figure IR-26. The liquid, vapor and CCl4 soln
spectra of hexanoic acid:
CH3(CH2)4 CO2H

13. The C=O stretching frequency
aliphatic amides

14. A summary of the principle infrared bands and their assignments
A summary of the principle infrared bands and their assignments. R is an aliphatic group.

15. KBr pellet
Amide I 
1662 cm-1
Amide II; 1634 cm-1

16. Secondary Amide
Figure IR-21. N-Methyl acetamide, neat liquid; thin film: CH3CONHCH3

17. Tertiary Amide
Figure IR-23. N,N-Dimethylacetamide, neat liquid; thin film: CH3CON(CH3)2

18. The C=O stretching frequency
anhydrides

19. A summary of the principle infrared bands and their assignments
A summary of the principle infrared bands and their assignments. R is an aliphatic group.

20. Figure IR-36. Propionic anhydride, neat liquid: CH3CH2CO2COCH2CH3
Anhydrides
Figure IR-36. Propionic anhydride, neat liquid: CH3CH2CO2COCH2CH3

21. The C=O stretching frequency
carboxylates

22. A summary of the principle infrared bands and their assignments
A summary of the principle infrared bands and their assignments. R is an aliphatic group.

23. C=O in an acid 1700 cm-1; C-O-C stretch 1300 to 1000 cm-1,
say in ethers  1150 cm-1. Averaging a C=O with a C-O-C results in: ( )/2 = 1425 cm-1. Naively, we would estimate a bond and a half would have a frequency of 1425 cm-1

24. 1410 cm-1
1560 cm-1
( )/2 = cm-1

26. The C=C bond stretch

27. A summary of the principle infrared bands and their assignments
A summary of the principle infrared bands and their assignments. R is an aliphatic group.

30. Figure IR-9. 1-Heptene; neat sample, thin film:
H2C=CH-CH2CH2CH2CH2CH3

31. The C=C bond stretch when next to a heteroatom

32. A summary of the principle infrared bands and their assignments
A summary of the principle infrared bands and their assignments. R is an aliphatic group.

33. Figure IR-40. 2,5-Dimethoxy2,5-dihydrofuran, neat liquid:

34. Figure IR-41. 2,3-Dihydrofuran, neat liquid:

36. The cumulative C=C bond stretch

38. The NO2 stretching frequency

39. A summary of the principle infrared bands and their assignments
A summary of the principle infrared bands and their assignments. R is an aliphatic group.

41. Aromatic Rings
Ring breathing motions
Both often appear as doublets

42. Benzene, neat, thin film:

44. 4-Chloro-2-nitrophenol, KBr pellet: