Spectroscopy

1. Spectroscopy PART I: Introduction and Infrared Spectroscopy Organic Chemistry 30B

2. Spectroscopy Spectroscopy is the study of the interaction of electromagnetic radiation and matter Molecular Spectroscopy is the study of which frequencies of radiation are absorbed or emitted by a substance and the correlation of those frequencies with molecular structure

3. Energy, Wavelength, Frequency Key relationships for electromagnetic radiation: E = h? = hc/? E = energy h = Planck’s constant c = Speed of light ? = Frequency ? = Wavelength

4. Energy, Wavelength, Frequency Key relationships: E = h? = hc/? Increase Frequency (?) --> Increase Energy Decrease Frequency (?) --> Decrease Energy Increase Wavelength (?) --> Decrease Energy Decrease Wavelength (?) --> Increase Energy

5. Energy, Wavelength, Frequency

6. Wavelength Units

7. Absorption of Energy by Molecules

8. Effects of Electromagnetic Radiation on Molecules Radiation Outcome hn 109 nm Radiowave Nuclear Spin Flips hn 106 nm Microwave Molecular Rotation hn 104 nm Infrared Bond Vibrations hn 500 nm Visible Electronic Excitation hn 200 nm Ultraviolet Electronic Excitation hn 10 nm X-ray Molecular Ionization hn 0.1 nm Gamma Ray Bond Cleavage

9. Infrared Spectroscopy Absorption of Infrared light in the wavelength range of 2.5x10-6 m to 2.5x 10-5 m (2.5 ?m to 25 ?m) causes bond vibrations Specific wavelengths (or frequencies) can be correlated with specific functional groups

10. Infrared Spectroscopy Infrared Spectrometer

11. Infrared Spectrum

12. Infrared Spectrum Units

13. Bond Vibrations for CH2

14. Bond Vibrations for CH2

15. Bond Vibrations for CH2

16. Theory of Bond Vibrations A vibrating bond can be thought of as two masses connected by a spring

17. Absorption Frequencies

18. Functional Group Absorbances

19. Functional Group Absorbances

20. Absorption Frequencies

21. Comparison of IR Spectra

22. Comparison of IR Spectra

23. IR Spectrum of Decane

24. IR Spectrum of Cyclohexene

25. IR Spectrum of 1-Octyne

26. IR Spectrum of Toluene

27. IR Spectrum of Anisole

28. IR Spectrum of Dibutyl Ether

29. IR Spectrum of 1-Hexanol

30. IR Spectrum of 1-Hexanol

31. IR Spectrum of 1-Butanamine

32. IR Spectrum of Menthone

33. IR Spectrum of Pentanoic Acid

34. IR Spectrum of Ethyl Butanoate

35. Sample IR Spectra

36. Details of Carbonyl Groups C=O Stretching Frequency: Cyclohexanone 1715 cm-1 Cyclopentanone 1745 cm-1 Cyclobutanone 1780 cm-1 Cyclopropanone 1850 cm-1 Cyclohexenone 1695 cm-1

37. Details of Carbonyl Groups - 2 Functional Group Frequencies Ketone C=O 1630-1820 cm-1 Aldehyde C=O 1630-1820 cm-1 C-H 2720 cm-1 Acid C=O 1700-1725 cm-1 O-H 2500-3300 cm-1 Ester C=O 1735-1800 cm-1 C-O 1000-1100 (sp3) or 1200-1250 cm-1 (sp2)

38. Interpreting Infrared Spectra Check for signals near 3000 cm-1 Alkanes vs alkenes vs alkynes Check for signals near 3400 cm-1 OH vs NH vs NH2 Check for signals near 1700 cm-1 Aldehyde vs ketone vs ester vs acid vs amide The principle goal will be identification of functional groups

39. Sample IR Problem 1 Identify functional groups present in molecule using IR spectrum.

40. Sample IR Problem 1 Identify functional groups present in molecule using IR spectrum.

41. Sample IR Problem 1 Identify functional groups present in molecule using IR spectrum.

42. Sample IR Problem 1 Identify functional groups present in molecule using IR spectrum.

43. Sample IR Problem 1 Identify functional groups present in molecule using IR spectrum.

44. Sample IR Problem 1 Identify functional groups present in molecule using IR spectrum.

45. Sample IR Problem 1 Identify functional groups present in molecule using IR spectrum.

46. Sample IR Problem 2 An unknown has the molecular formula C10H15N. Is the amine primary (R-NH2), secondary (R2N-H), or tertiary (R3N)?

47. Sample IR Problem 2 An unknown has the molecular formula C10H15N. Is the amine primary (R-NH2), secondary (R2N-H), or tertiary (R3N)?

48. Sample IR Problem 2 An unknown has the molecular formula C10H15N. Is the amine primary (R-NH2), secondary (R2N-H), or tertiary (R3N)?

49. Sample IR Problem 3 An unknown has the molecular formula C8H11N. Is the amine primary (R-NH2), secondary (R2N-H), or tertiary (R3N)?

50. Sample IR Problem 3 An unknown has the molecular formula C8H11N. Is the amine primary (R-NH2), secondary (R2N-H), or tertiary (R3N)?

51. Sample IR Problem 3 An unknown has the molecular formula C8H11N. Is the amine primary (R-NH2), secondary (R2N-H), or tertiary (R3N)?

52. Sample IR Problem 4 An unknown has the molecular formula C8H11N. Is the amine primary (R-NH2), secondary (R2N-H), or tertiary (R3N)?

53. Sample IR Problem 4 An unknown has the molecular formula C8H11N. Is the amine primary (R-NH2), secondary (R2N-H), or tertiary (R3N)?

54. Sample IR Problem 4 An unknown has the molecular formula C8H11N. Is the amine primary (R-NH2), secondary (R2N-H), or tertiary (R3N)?

55. Sample IR Problem 5 An unknown has the molecular formula C4H8O. Therefore DBE = 1. Is it an alcohol, ketone, or ether? Is there an alkene or is it cyclic?

56. Sample IR Problem 5 An unknown has the molecular formula C4H8O. Therefore DBE = 1. Is it an alcohol, ketone, or ether? Is there an alkene or is it cyclic?

57. Sample IR Problem 5 An unknown has the molecular formula C4H8O. Therefore DBE = 1. Is it an alcohol, ketone, or ether? Is there an alkene or is it cyclic?

58. Sample IR Problem 5 An unknown has the molecular formula C4H8O. Therefore DBE = 1. Is it an alcohol, ketone, or ether? Is there an alkene or is it cyclic?

59. Sample IR Problem 5 An unknown has the molecular formula C4H8O. Therefore DBE = 1. Is it an alcohol, ketone, or ether? Is there an alkene or is it cyclic?

60. End