1. Infrared Radiation: Molecular Vibrations1

2. Electromagnetic Radiation: Light, Energy, Heat IR Tutor:

3. What do the sun’s energy, a molecule’s shape and a TV remote have to do with greenhouse gases?

4. Infrared Absorbance

5. Infrared Absorbance TV
Remote

6. Infrared Absorbance
Sample TV
Remote

7. Infrared Absorbance & Molecular Vibrations for CCl4 Stretching & Bending

8. Infrared Spectroscopy1

9. Infrared Absorbance

10. IR- Empirical Comparisons
Identifying functional groups in organic molecules

11. Infrared Spectroscopy
Region of infrared that is most useful lies between mm ( cm-1)
depends on transitions between vibrational energy states
Stretching: higher energy / higher wave number (cm-1)
Bending: lower energy / lower wave number (cm-1) 2

12. A bond must have a dipole or an induced dipole in order to have an absorbance in the IR spectrum.
When the bond stretches, the increasing distance
between the atoms increases the dipole moment.
Therefore, the greater the dipole, the more intense the absorption. (i.e., The greater the molar extinction coefficient () in Beer’s law, A = bc.

13. Functions & Infrared Spectra
Analyzing Structure:
Functions & Infrared Spectra
The molecular formula is a critical piece of information, which limits the functional possibilities.
The presence & absence of absorption bands must be considered in identifying a possible structure in IR spectroscopy. Empiricism is critical to successful identification.
NOTE: Bonds which lack dipole moments are not
detected.

14. Structural/Functional Components
Figure: UN
Caption:
The IR spectrum has distinct regions. The left of the spectrum shows the C-H, O-H, and N-H stretches. The triple bonds absorb around 2200 cm-1 followed by the double bonds to the right at around 1700 cm-1. The region below 1400 cm-1 is called the fingerprint region.

16. An Infrared Spectrum
The peaks are quantized absorption bands corresponding to molecular stretching and bending vibrations

17. The functional group
stretching region
The fingerprint
region

18. Infrared Absorption Frequencies
Structural unit Frequency, cm-1
Stretching vibrations (single bonds)
O—H (alcohols)
O—H (carboxylic acids)
First examine the absorption bands in the vicinity of
cm–1 8

20. 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

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

22. Cyclic aliphatic ketone

23. Mono substituted aromatic methyl ketone

24. Mono substituted aromatic ketone

25. Aliphatic ester I

26. Aliphatic ester II

27. Aliphatic ester III

28. Mono substituted aromatic ester

29. Mono substituted aromatic conjugated ester

30. Infrared Absorption Frequencies
Structural unit Frequency, cm-1
Stretching vibrations (single bonds)
sp2 C—O 1200
sp3 C—O 8

31. Dihexyl Ether
~1100 cm-1
cm-1 8

32. Carboxylic Acid
~1200 cm-1

33. Distinctive Stretch of C–H Bond in an Aldehyde (the “waggle” vibration)

34. Aliphatic aldehyde

35. Mono-substituted aromatic aldehyde

36. Mono substituted aromatic ester

37. Para di-substituted aromatic ether & aldehyde

38. Infrared Spectroscopy Common Functional Groups Handout1

39. Acetate Esters: Smell / Pheromones
Pheromone Synthesis
[20:40-23:51]

40. Infrared Spectroscopy Common Functional Groups Questions1

41. 2,4,6-cycloheptaheptatrien-1-one
Question #1
C7H6O
Identify the compound from the IR above.
benzyl alcohol
2,4,6-cycloheptaheptatrien-1-one
acetophenone
benzaldehyde
phenylacetic acid

42. 2,4,5-trimethylbenzaldehyde
Question #2
C10H12O
Identify the compound from the IR above.
2,4,5-trimethylbenzaldehyde
p-allylanisole
2-allyl-4methylphenol
1-phenyl-2-butanone

43. Question #3 Identify the compound from the IR above. cyclopropanone
C3H4O
Identify the compound from the IR above.
cyclopropanone
propynol
acrylaldehyde
propenoic acid

44. Question #4 Identify the compound from the IR above. methylbenzoate
C8H8O2
Identify the compound from the IR above.
methylbenzoate
o-hydroxyacetophenone
o-toluic acid
p-anisaldehyde (p-methoxybenzaldehyde)

45. Question #5 Identify the compound from the IR above. benzylformate
C8H8O2
Identify the compound from the IR above.
benzylformate
o-hydroxyacetophenone
2-methoxytropone
p-toluic acid
o-anisaldehyde (p-methoxybenzaldehyde)