1. 1 CHAPTER 9 Spectroscopy: the study of the interaction of energy with matter Energy applied to matter can be absorbed, emitted, cause a chemical change, or be transmitted Spectroscopy can be used to elucidate the structure of a molecule

2. 2 Electromagnetic radiation Electromagnetic radiation is the energy that is transmitted through space in the form of waves.. Types of electromagnetic radiation: Radio waves, Ultraviolet (UV), Infrared(IR), Visible (vis).

3. 3 Characterization of waves Waves are characterized by: 1-Wavelength (λ): the distance from the crest of one wave to the crest of the next wave. λ = nm,um, cm

4. 4 2- the waves are also characterized by Frequency (v)= number of complete cycles per second (cps), also called Hertz (Hz).

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6. 6 Wavelength and frequency are inversely proportional. In IR,frequency is expressed as wavenumbers Wavenumbers have units of reciprocal cm (cm -1 )

7. 7 The relationship between wavelength (or frequency) and energy (E) is well defined 1- Wavelength and frequency are inversely proportional. 2- The higher the frequency, the greater the energy of the wave. 3- The shorter the wavelength, the greater the energy of the wave.

8. 8 UVVISIRRADIO waves Increasing wavelength-Decreasing frequencyDecreasing Energy Absorption of UV  Result of promotion of electron to a higher energy level Absorption of IR  Result in increase of vibration of bonds

9. 9 Features of a spectrum An infrared spectrum of a compound is a plot of percent transmission (%T) versus either wavelength of frequency changing. %T = (Intensity/original intensity) x 100

10. 10 Absorption of Infrared Radiation  Cause increase the vibration of bonded atoms  Different type of bonds ( C-H, C-C, C-O, C=O, O-H) absorb IR at different λ.  Type of vibration absorb at different λ. Types of vibrations 1-stretching 2-bending

11. 11 The relative amount of absorbed energy depends on the change of bond moment 1)Non-polar bonds  weak absorption 2)Polar bonds  strong absorption

12. 12 The infrared spectrum The instrument used to measure absorption of infrared radiation  infrared spectrophotometer

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14. 14 Interpretation of IR spectrum Correlation Chart

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16. 16 A.c-c Bonds C-C single bond  weak absorption (not useful) C=C (sp 2 )  1600- 1700 cm -1 C=C( aryl, sp2)  1450-1600cm -1

17. 17 C-H Bonds (sp3) C-H  2800-3000cm -1 (sp2) C-H (=C-H)  3000-3300 cm -1

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21. 21 Aromatic Compounds –Aromatic Compounds The C-C bond stretching gives a set of characteristic sharp peaks between 1450-1600 cm -1

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23. 23 Haloalkanes: C-X  500-1430cm -1

24. 24 Ether:C-O  1050-1260 cm -1 (strong)

25. 25 Alcohol:O-H  3000-3600cm -1 (strong) + C-O

26. 26 Hydrogen bonding  O-H broad No H-bonding  O-H sharp

27. 27 Amines: RNH 2  3000-3600cm -1 (medium or weak double peaks) + C-N (900-1300 CM -1 )

28. 28 Amines: R 2 NH  3000-3600cm -1 (medium or weak one peak) + C-N (900-1300cm -1 )

29. 29 Amines: R 3 N  no N-H peak only C- N at 900-1300cm -1

30. 30 Carbonyl Functional Groups Generally the carbonyl group gives a strong peak which occurs at 1630-1780 cm -1  The exact location depends on the actual functional group present

31. 31 Ketones: C=O  1680-1750 cm -1 (strong)

32. 32 Aldehydes: Carbonyl (C=O) 1720-1740cm -1 Also must show aldehyde C-H bend Two peaks 1) 2820-2900cm -1 2) 2700-2780 cm -1

33. 33 Carboxylic acid: carbonyl (C=O)  1700-1725 cm -1 (strong) Also must show O-H stretching  very broad from 3330- 2500 cm -1

34. 34 Esters: C=O  1735-1760 cm -1 Also shows C-O  1100-1300 cm -1

35. 35 Conclusion IR is used for functional groups identification. Not all the peaks can be analyzed. Example

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