University of North Florida

HSC 3578

CHAPTER 12 INFRARED SPECTROSCOPY

MULTIPLE CHOICE

1)Which of the following regions in the electromagnetic spectrum corresponds to the radiation with the highest energy?

1. 1. radio waves
   2. ultraviolet
   3. infrared
   4. visible
2. Which of the following regions in the electromagnetic spectrum corresponds to the radiation with the longest wavelength?
   1. radio waves
   2. ultraviolet
   3. infrared
   4. visible
3. What range of wavelengths corresponds to the infrared region of the electromagnetic spectrum? a.        200-400 nm

b. 400-700 nm

c.     2.5-50 ?m

d. 2-10 mm

4. Which of the following processes takes place upon absorption of infrared radiation?
   1. bond vibration
   2. electron excitation
   3. nuclear spin flip
   4. electron spin flip

5. 

   What are the units of wavenumber, , in infrared spectroscopy?
   1. cm
   2. cm^?1
   3. J?mol^?1
   4. none, wavenumber is a dimensionless quantity
6. Which of the following relationships is not valid as applied to infrared spectroscopy?
   1. wavenumber = 1/? (in cm)
   2. ?E = h ?

c.     ?E = ? ?

d. ? = 4.12 ?(K/?)

7. Which of the following laws relates the frequency of a stretching vibration to the masses and spring constant of a simple harmonic oscillator?
   1. Pan's law
   2. Hooke's law
   3. Peter's law
   4. Barrie's law
8. What is required for a bond to give an infrared absorption?
   1. a change in bond length during vibration
   2. a change in bond angle during vibration
   3. a change in bond dipole during vibration
   4. a change in reduced mass during vibration
9. Which of the following bonds (circled) gives a very weak or no stretching absorption in the infrared spectrum?

1. 1. 1
   2. 2
   3. 3
   4. 4

10. Which of the following bonds gives the weakest peak in the infrared spectrum for a stretching vibration?

1. 1. 1
   2. 2
   3. 3
   4. 4

11. Which of the following bonds undergoes stretching at the highest frequency?
    1. C=O
    2. C?O
    3. C=C
    4. C?C

12. Which of the following bonds undergoes stretching at the highest frequency?
    1. O?H
    2. C?H
    3. C=O
    4. C?C
13. Which of the following carbon-carbon bonds undergoes stretching at the highest frequency?
    1. sp³ C ? sp³ C
    2. alkene sp² C ? sp² C
    3. arene sp² C ? sp² C
    4. C?C
14. Which of the following bonds (circled) vibrates at the highest frequency?

1. 1. 1
   2. 2
   3. 3
   4. 4

15. Which of the following bonds (circled) gives the weakest absorbance in the infrared spectrum?

1. 1. 1
   2. 2
   3. 3
   4. 4

16. Which of the following bonds gives rise to a strong absorbance at approximately 1630-1820 cm^?1 in the infrared spectrum?
    1. C=O
    2. C?O
    3. C=C
    4. C?C

17. Which of the following bonds gives rise to an absorbance at approximately 2700-3300 cm^?1 in the infrared spectrum?
    1. C?C
    2. C=O
    3. C=C
    4. C?H
18. Which of the following bonds gives rise to a strong, broad, absorbance at approximately 3200-3650 cm^?1 in the infrared spectrum?
    1. C=O
    2. O?H
    3. C=C
    4. C?H
19. Which of the following bonds gives rise to a medium strength absorbance at approximately 1600-1680 cm^?1 in the infrared spectrum?
    1. C?H
    2. C?C
    3. C=C
    4. C?C
20. Which of the following functional groups is likely to be present in a molecule that has peaks in the infrared spectrum at 1630-1820 cm^?1 (strong, broad) and 1000-1250 cm^?1; but does not have peaks at 3200-3650 cm^?1?
    1. alcohol
    2. aldehyde or ketone
    3. ether
    4. ester
21. Which of the following functional groups is likely to be present in a molecule that has peaks in the infrared spectrum at 1630-1820 cm^?1 (strong, broad), but does not have peaks at 3200-3650 or 1000-1250 cm^?1
    1. alcohol
    2. aldehyde or ketone
    3. ether
    4. ester
22. Which of the following functional groups is likely to be present in a molecule that has peaks in the infrared spectrum at 3200-3650 cm^?1 (strong), but does not have peaks at 1630-1820 or 1000-1250 cm?1
    1. alcohol
    2. aldehyde or ketone
    3. ether
    4. ester

23. Which of the following functional groups is likely to be present in a molecule that has peaks in the infrared spectrum at 1000-1250 cm^?1 (strong), but does not have peaks 3200-3650 at 1630-1820 or cm^?1?
    1. alcohol
    2. aldehyde or ketone
    3. ether
    4. ester
24. Which of the following compounds gives an infrared spectrum with peaks in the ranges of 3200-3650 (strong, broad) and 1600-1640 cm^?1 (medium); but does not have peaks at 1630-1820 (strong)?

1. 1. 1
   2. 2
   3. 3
   4. 4

25. Which of the following compounds gives an infrared spectrum with a peak in the range of 1630-1820 cm^?1 (strong peak), but does not have peaks at 3200-3650 or 1000-1250 cm^?1?

1. 1. 1
   2. 2
   3. 3
   4. 4

26. Which of the following compounds gives an infrared spectrum with peaks at 1000-1250 cm^?1 (strong), but does not have peaks at 3200-3650 or 1630-1820 cm^?1 (sharp, weak peak)?

1. 1. 1
   2. 2
   3. 3
   4. 4

27. Which of the following compounds gives an infrared spectrum with peaks in the ranges of 3200-3650 (strong, broad), but does not have peaks at 1630-1820 (strong) or 1600-1640 cm^?1 (medium)?

1. 1. 1
   2. 2
   3. 3
   4. 4

28. Which of the following compounds gives an infrared spectrum with peaks at 3300 cm^?1 (sharp peak) and 2150 cm^?1 (sharp peak)?

1. 1. 1
   2. 2
   3. 3
   4. 4

29. Which of the following compounds gives an infrared spectrum with no significant peaks at ~3300 cm^?1 or 1600-1680 cm^?1?

1. 1. 1
   2. 2
   3. 3
   4. 4

30. Which of the following compounds gives an infrared spectrum with peaks at 3000-3500 cm^?1 and

~1750 cm^?1?

1. 1. 1
   2. 2
   3. 3
   4. 4

31. Which of the following compounds gives an infrared spectrum with a peak at ~1750 cm^?1, but no significant peaks at 3000-3500 cm^?1 or 1050-1250 cm^?1?

1. 1. 1
   2. 2
   3. 3
   4. 4

32. Which of the following compounds does not give an infrared spectrum with peak at ~1750 cm^?1?

1. 1. 1
   2. 2
   3. 3
   4. 4

33. Which of the following compounds gives a carbonyl bond absorption at the highest frequency?

1. 1. 1
   2. 2
   3. 3
   4. 4

34. Which of the following compounds gives a carbonyl bond absorption at the highest frequency?

1. 1. 1
   2. 2
   3. 3
   4. 4

35. Which of the following compounds gives a carbonyl bond absorption at the lowest frequency?

1. 1. 1
   2. 2
   3. 3
   4. 4

PROBLEM

1. Provide the structure of three compounds with the molecular formula C₄H₈O that give an absorption peak at 1600-1640 cm^-1 in the infrared spectrum, but no signicant peaks at 3000-3600 cm^-1 or at 1650-1750 cm^-1.

Any three of the following:

2. Provide the structure of four compounds with the molecular formula C₅H₁₀O which give a strong absorption peak at 1700-1740 cm^-1 in the infrared spectrun, but no signicant peaks at 1600-1640 cm^-1 .

Any four of the following:

3. Provide a brief explanation to account for the observation that 1-butyne gives a significantly stronger peak at ~1250 cm^-1 in the infrared spectrum than 2-butyne..

4. Provide a brief explanation to account for the observation that the frequency of the C=O stretching absorption in the infrared spectrum of 2-butanone is higher than that of 3-buten-2-one.

5. Provide a brief explanation to account for the observation that the frequency of the C=O stretching absorption in the infrared spectrum of N,N-dimethylacetamide, CH₃CON(CH₃)₂, is higher than that of methyl acetate, CH₃CO₂CH₃.

6. How could you distingish between 1-hexyne and 2-hexyne by infrared spectroscopy?

7. How could you distingish between 1-butanol and diethyl ether by infrared spectroscopy?

8. How could you distingish between methyl butanoate and pentanoic acid by infrared spectroscopy?

9. Label three peaks in the following spectrum with the bond that gives rise to them, and identify the functional group that is present in the compound (the compound has a formula of C₆H₁₄O)?