1. Dr. Wolf's CHM 201 & 202 13- 1 Chapter 13 Spectroscopy Infrared spectroscopy Ultraviolet-Visible spectroscopy Nuclear magnetic resonance spectroscopy Mass Spectrometry

2. Dr. Wolf's CHM 201 & 202 13- 2 13.1 Principles of Molecular Spectroscopy: Electromagnetic Radiation

3. Dr. Wolf's CHM 201 & 202 13- 3 is propagated at the speed of light has properties of particles and waves the energy of a photon is proportional to its frequency Electromagnetic Radiation

4. Dr. Wolf's CHM 201 & 202 13- 4 Figure 13.1: The Electromagnetic Spectrum 400 nm750 nm Visible Light Longer Wavelength ( )Shorter Wavelength ( ) Higher Frequency ( )Lower Frequency ( ) Higher Energy (E)Lower Energy (E)

5. Dr. Wolf's CHM 201 & 202 13- 5 Figure 13.1: The Electromagnetic Spectrum UltravioletInfrared Longer Wavelength ( ) Shorter Wavelength ( ) Higher Frequency ( ) Lower Frequency ( ) Higher Energy (E) Lower Energy (E)

6. Dr. Wolf's CHM 201 & 202 13- 6 Cosmic rays  Rays X-rays Ultraviolet light Visible light Infrared radiation Microwaves Radio waves Cosmic rays  Rays X-rays Ultraviolet light Visible light Infrared radiation Microwaves Radio waves Figure 13.1: The Electromagnetic Spectrum Energy

7. Dr. Wolf's CHM 201 & 202 13- 7 13.2 Principles of Molecular Spectroscopy: Quantized Energy States

8. Dr. Wolf's CHM 201 & 202 13- 8 Electromagnetic radiation is absorbed when the energy of photon corresponds to difference in energy between two states.  E = h  E = h

9. Dr. Wolf's CHM 201 & 202 13- 9 electronicvibrationalrotational nuclear spin UV-Visinfraredmicrowaveradiofrequency What Kind of States?

10. Dr. Wolf's CHM 201 & 202 13- 10 13.20 - 13.22 Infrared Spectroscopy Gives information about the functional groups in a molecule

11. Dr. Wolf's CHM 201 & 202 13- 11 region of infrared that is most useful lies between 2.5-16  m (4000-625 cm -1 ) depends on transitions between vibrational energy states stretchingbending Infrared Spectroscopy

12. Dr. Wolf's CHM 201 & 202 13- 12 Stretching Vibrations of a CH 2 Group SymmetricAntisymmetric

13. Dr. Wolf's CHM 201 & 202 13- 13 Bending Vibrations of a CH 2 Group In plane

14. Dr. Wolf's CHM 201 & 202 13- 14 Bending Vibrations of a CH 2 Group Out of plane

15. Dr. Wolf's CHM 201 & 202 13- 15 Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved.200035003000250010001500500 Wave number, cm -1 Figure 13.31: Infrared Spectrum of Hexane CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 C—H stretching bending

16. Dr. Wolf's CHM 201 & 202 13- 16200035003000250010001500500 Wave number, cm -1 Figure 13.32: Infrared Spectrum of 1-Hexene H 2 C=CHCH 2 CH 2 CH 2 CH 3 H—C C=C—H C=C H 2 C=C Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved.

17. Dr. Wolf's CHM 201 & 202 13- 17 Structural unitFrequency, cm -1 Stretching vibrations (single bonds) sp C—H3310-3320 sp 2 C—H3000-3100 sp 3 C—H2850-2950 sp 2 C—O1200 sp 3 C—O1025-1200 Infrared Absorption Frequencies

18. Dr. Wolf's CHM 201 & 202 13- 18 Structural unitFrequency, cm -1 Stretching vibrations (multiple bonds) Infrared Absorption Frequencies C C 1620-1680—CN —CC— 2100-2200 2240-2280

19. Dr. Wolf's CHM 201 & 202 13- 19 Structural unitFrequency, cm -1 Stretching vibrations (carbonyl groups) Aldehydes and ketones1710-1750 Carboxylic acids1700-1725 Acid anhydrides1800-1850 and 1740-1790 Esters1730-1750 Amides1680-1700 Infrared Absorption Frequencies C O

20. Dr. Wolf's CHM 201 & 202 13- 20 Structural unitFrequency, cm -1 Bending vibrations of alkenes Infrared Absorption Frequencies CH 2 RCH R2CR2CR2CR2C CHR' cis-RCH CHR' trans-RCH CHR' R2CR2CR2CR2C910-990 890 665-730 960-980 790-840

21. Dr. Wolf's CHM 201 & 202 13- 21 Structural unitFrequency, cm -1 Bending vibrations of derivatives of benzene Monosubstituted730-770 and 690-710 Ortho-disubstituted735-770 Meta-disubstituted750-810 and 680-730 Para-disubstituted790-840 Infrared Absorption Frequencies

22. Dr. Wolf's CHM 201 & 202 13- 22200035003000250010001500500 Wave number, cm -1 Figure 13.33: Infrared Spectrum of tert-butylbenzene H—C Ar—H Monsubstituted benzene C 6 H 5 C(CH 3 ) 3 Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved.

23. Dr. Wolf's CHM 201 & 202 13- 23 Structural unitFrequency, cm -1 Stretching vibrations (single bonds) O—H (alcohols)3200-3600 O—H (carboxylic acids) 3000-3100 N—H3350-3500 Infrared Absorption Frequencies

24. Dr. Wolf's CHM 201 & 202 13- 24200035003000250010001500500 Wave number, cm -1 Figure 13.34: Infrared Spectrum of 2-Hexanol H—C O—H OH CH 3 CH 2 CH 2 CH 2 CHCH 3 Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved.

25. Dr. Wolf's CHM 201 & 202 13- 25200035003000250010001500500 Wave number, cm -1 Figure 13.35: Infrared Spectrum of 2-Hexanone H—C C=O O CH 3 CH 2 CH 2 CH 2 CCH 3 Francis A. Carey, Organic Chemistry, Fifth Edition. Copyright © 2003 The McGraw-Hill Companies, Inc. All rights reserved.

26. Dr. Wolf's CHM 201 & 202 13- 26 13.23 Ultraviolet-Visible (UV-VIS) Spectroscopy Gives information about conjugated  electron systems

27. Dr. Wolf's CHM 201 & 202 13- 27 gaps between electron energy levels are greater than those between vibrational levels gap corresponds to wavelengths between 200 and 800 nm Transitions between electron energy states  E = h  E = h

28. Dr. Wolf's CHM 201 & 202 13- 28 X-axis is wavelength in nm (high energy at left, low energy at right) max is the wavelength of maximum absorption and is related to electronic makeup of molecule— especially  electron system max is the wavelength of maximum absorption and is related to electronic makeup of molecule— especially  electron system Y axis is a measure of absorption of electromagnetic radiation expressed as molar absorptivity (  ) Conventions in UV-VIS

29. Dr. Wolf's CHM 201 & 202 13- 29 200220240260280 1000 2000 Wavelength, nm max 230 nm max 230 nm  max 2630 Molar absorptivity (  ) UV Spectrum of cis,trans-1,3-cyclooctadiene

30. Dr. Wolf's CHM 201 & 202 13- 30 Most stable  -electron configuration  -Electron configuration of excited state          * Transition in cis,trans-1,3-cyclooctadiene HOMO LUMO  E = h  E = h

31. Dr. Wolf's CHM 201 & 202 13- 31  * Transition in Alkenes HOMO-LUMO energy gap is affected by substituents on double bond as HOMO-LUMO energy difference decreases (smaller  E), max shifts to longer wavelengths

32. Dr. Wolf's CHM 201 & 202 13- 32 Methyl groups on double bond cause max to shift to longer wavelengths C C H H H H C C H H CH 3 max 170 nm max 170 nm CH 3 max 188 nm max 188 nm

33. Dr. Wolf's CHM 201 & 202 13- 33 Extending conjugation has a larger effect on max ; shift is again to longer wavelengths C C H H H H C C H H max 170 nm max 170 nm max 217 nm max 217 nm H C C H H H

34. Dr. Wolf's CHM 201 & 202 13- 34 max 217 nm (conjugated diene) max 217 nm (conjugated diene) H C CHH C C H H H C C H CH 3 H H C C H3CH3CH3CH3CH C C H H max 263 nm conjugated triene plus two methyl groups max 263 nm conjugated triene plus two methyl groups

35. Dr. Wolf's CHM 201 & 202 13- 35 LycopeneLycopene max 505 nm max 505 nm orange-red pigment in tomatoes

36. Dr. Wolf's CHM 201 & 202 13- 36 13.24 Mass Spectrometry

37. Dr. Wolf's CHM 201 & 202 13- 37 Atom or molecule is hit by high-energy electron Principles of Electron-Impact Mass Spectrometry e–e–e–e–

38. Dr. Wolf's CHM 201 & 202 13- 38 Atom or molecule is hit by high-energy electron electron is deflected but transfers much of its energy to the molecule e–e–e–e– Principles of Electron-Impact Mass Spectrometry

39. Dr. Wolf's CHM 201 & 202 13- 39 Atom or molecule is hit by high-energy electron electron is deflected but transfers much of its energy to the molecule e–e–e–e– Principles of Electron-Impact Mass Spectrometry

40. Dr. Wolf's CHM 201 & 202 13- 40 This energy-rich species ejects an electron. Principles of Electron-Impact Mass Spectrometry

41. Dr. Wolf's CHM 201 & 202 13- 41 This energy-rich species ejects an electron. Principles of Electron-Impact Mass Spectrometry forming a positively charged, odd-electron species called the molecular ion e–e–e–e– +

42. Dr. Wolf's CHM 201 & 202 13- 42 Molecular ion passes between poles of a magnet and is deflected by magnetic field amount of deflection depends on mass-to-charge ratio highest m/z deflected least lowest m/z deflected most Principles of Electron-Impact Mass Spectrometry +

43. Dr. Wolf's CHM 201 & 202 13- 43 Principles of Electron-Impact Mass Spectrometry If the only ion that is present is the molecular ion, mass spectrometry provides a way to measure the molecular weight of a compound and is often used for this purpose. However, the molecular ion often fragments to a mixture of species of lower m/z.

44. Dr. Wolf's CHM 201 & 202 13- 44 The molecular ion dissociates to a cation and a radical. Principles of Electron-Impact Mass Spectrometry +

45. Dr. Wolf's CHM 201 & 202 13- 45 The molecular ion dissociates to a cation and a radical. Principles of Electron-Impact Mass Spectrometry + Usually several fragmentation pathways are available and a mixture of ions is produced.

46. Dr. Wolf's CHM 201 & 202 13- 46 mixture of ions of different mass gives separate peak for each m/z intensity of peak proportional to percentage of each ion of different mass in mixture separation of peaks depends on relative mass Principles of Electron-Impact Mass Spectrometry + + + + + +

47. Dr. Wolf's CHM 201 & 202 13- 47 mixture of ions of different mass gives separate peak for each m/z intensity of peak proportional to percentage of each atom of different mass in mixture separation of peaks depends on relative mass ++++ ++ Principles of Electron-Impact Mass Spectrometry

48. Dr. Wolf's CHM 201 & 202 13- 48 20406080100 120 m/z m/z = 78 10080 60 40 20 0 Relative intensity Some molecules undergo very little fragmentation Benzene is an example. The major peak corresponds to the molecular ion.

49. Dr. Wolf's CHM 201 & 202 13- 49 HHH HH H HHH HH H HHH HH H all H are 1 H and all C are 12 C one C is 13 C one H is 2 H Isotopic Clusters 78 7979 93.4%6.5%0.1%

50. Dr. Wolf's CHM 201 & 202 13- 50 20406080100 120 m/z10080 60 40 20 0 Relative intensity 112 114 Isotopic Clusters in Chlorobenzene visible in peaks for molecular ion 35 Cl 37 Cl

51. Dr. Wolf's CHM 201 & 202 13- 51 20406080100 120 m/z Relative intensity 77 Isotopic Clusters in Chlorobenzene no m/z 77, 79 pair; therefore ion responsible for m/z 77 peak does not contain Cl H H H H H+ 10080 60 40 20 0

52. Dr. Wolf's CHM 201 & 202 13- 52 Alkanes undergo extensive fragmentation m/z Decane 142 43 57 71 85 99 CH 3 —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —CH 2 —CH 3 Relative intensity 10080 60 40 20 0 20406080100 120

53. Dr. Wolf's CHM 201 & 202 13- 53 Propylbenzene fragments mostly at the benzylic position 20406080100 120 m/z Relative intensity 120 91 CH 2 —CH 2 CH 3 10080 60 40 20 0

54. Dr. Wolf's CHM 201 & 202 13- 54 13.25 Molecular Formula as a Clue to Structure

55. Dr. Wolf's CHM 201 & 202 13- 55 Molecular Weights One of the first pieces of information we try to obtain when determining a molecular structure is the molecular formula. However, we can gain some information even from the molecular weight. Mass spectrometry makes it relatively easy to determine molecular weights.

56. Dr. Wolf's CHM 201 & 202 13- 56 The Nitrogen Rule A molecule with an odd number of nitrogens has an odd molecular weight. A molecule that contains only C, H, and O or which has an even number of nitrogens has an even molecular weight. NH2NH2NH2NH2 93 138 NH2NH2NH2NH2 O2NO2NO2NO2N 183 NH2NH2NH2NH2 O2NO2NO2NO2N NO2NO2NO2NO2

57. Dr. Wolf's CHM 201 & 202 13- 57 Exact Molecular Weights CH 3 (CH 2 ) 5 CH 3 Heptane CH 3 CO O Cyclopropyl acetate Molecular formula Molecular weight C 7 H 16 C5H8O2C5H8O2C5H8O2C5H8O2 100100 Exact mass 100.1253100.0524 Mass spectrometry can measure exact masses. Therefore, mass spectrometry can give molecular formulas.

58. Dr. Wolf's CHM 201 & 202 13- 58 Molecular Formulas Knowing that the molecular formula of a substance is C 7 H 16 tells us immediately that is an alkane because it corresponds to C n H 2n+2 C 7 H 14 lacks two hydrogens of an alkane, therefore contains either a ring or a double bond

59. Dr. Wolf's CHM 201 & 202 13- 59 Index of Hydrogen Deficiency relates molecular formulas to multiple bonds and rings index of hydrogen deficiency = 1 2 (molecular formula of alkane – molecular formula of compound)

60. Dr. Wolf's CHM 201 & 202 13- 60 Example 1 index of hydrogen deficiency C 7 H 14 12 (molecular formula of alkane – molecular formula of compound) = 12 (C 7 H 16 – C 7 H 14 ) = 12 (2) = 1 = Therefore, one ring or one double bond.

61. Dr. Wolf's CHM 201 & 202 13- 61 Example 2 C 7 H 12 12 (C 7 H 16 – C 7 H 12 ) = 1 2 (4) = 2 = Therefore, two rings, one triple bond, two double bonds, or one double bond + one ring.

62. Dr. Wolf's CHM 201 & 202 13- 62 Oxygen has no effect CH 3 (CH 2 ) 5 CH 2 OH (1-heptanol, C 7 H 16 O) has same number of H atoms as heptane index of hydrogen deficiency = 1 2 (C 7 H 16 – C 7 H 16 O) = 0 = 0 no rings or double bonds

63. Dr. Wolf's CHM 201 & 202 13- 63 Oxygen has no effect index of hydrogen deficiency = 1 2 (C 5 H 12 – C 5 H 8 O 2 ) = 2 = 2 one ring plus one double bond CH 3 CO O Cyclopropyl acetate

64. Dr. Wolf's CHM 201 & 202 13- 64 If halogen is present Treat a halogen as if it were hydrogen. C C CH 3 Cl H H C 3 H 5 Cl same index of hydrogen deficiency as for C 3 H 6

65. Dr. Wolf's CHM 201 & 202 13- 65 Rings versus Multiple Bonds Index of hydrogen deficiency tells us the sum of rings plus multiple bonds. Catalytic hydrogenation tells us how many multiple bonds there are.