Absorption spectroscopy

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Absorption spectroscopy

  1. 1. Absorption and Mass Spectroscopy Presenter: Cynthia Echefu
  2. 2. Absorption Spectroscopy Infrared (IR)- Used to determine functional groups (molecular vibration, which includes bending, stretching and rotation)Ultraviolet- Used to identify conjugated double bondsVisible – sequence of light color the eye can see
  3. 3. AAMC: Must know about IR• intramolecular vibrations and rotations• recognizing common characteristic group absorptions, fingerprint region
  4. 4. Infrared spectrumviolate , indigo, blue, green, yellow, orange, red
  5. 5. Vibrations: bonds can stretch, compress and bend like a spring. It is this vibration that is measured in IR-spec. Rotations: molecules can rotate. Rotations produce waves mainly in the microwave region. However, part of the rotation spectra does overlap with the vibration spectra.http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/InfraRed/infrared.htm
  6. 6. Wave number (1/ƛ) (cm-1)4000 500 3500 3000 2500 2000 1500 1000
  7. 7. Infrared Spectrum
  8. 8. Common functional group characteristics• Anything around 3000 cm-1 involves a hydrogen atom, be it O-H, N-H, or C-H.• Anything around 2000 cm-1 and below does not involve hydrogen, be it C=O, C=C, C-C, or C-O.• Remember this: 1700 cm-1 is for the carbonyl group..
  9. 9. Continues…• Remember this: 3300 cm-1 can be O- H, N-H, or alkyne C-H.• Broad peaks are due to hydrogen bonding (OH and NH).• Below 1100 cm-1 is called the fingerprint region.
  10. 10. Wave number (cm-1) Functional Group Wave number Fingerprint region Less than 1100 Carbon oxygen single bond (c-o) 1100 Carbon single bond (c-c) 1100 Carbon double bond (c=c) 1750 Aldehyde, ketone and acid (c=o) 1700- 1750Aliphatic hydrogen (non-aromatic) Less than 3000 Aromatic (or multiple bond) Greater than 3000 Alcohol (O-H) 3500 (broad) Amine (N-H) 3500 (slightly sharp) Alkynes (C-H) 3500 ( very sharp)
  11. 11. Must Know Alcohol (broad) Acid (sharp) Ketone (sharp)Amine (slightly sharp) Alkyne (C-H)(sharp)
  12. 12. AAMC: Must know about UV• π -electron and nonbonding electron transitions• conjugated systems
  13. 13. Ultraviolet Spectroscopy Electrons absorption UV energy, which causes the electrons totransition from a low energy level(ground state) to a higher energy level (excited state).
  14. 14. Bonding, non-bonding and anti-bonding• Electron excitation
  15. 15. Ultraviolet Spectroscopy Conjugated vs. isolated double bonds• Conjugated (single bond between two double bonds) C=C-C=C• Isolated (two or more single bonds between double bonds) C=C-C-C=C
  16. 16. AAMC: Must know about visible• absorption in visible region yielding complementary color• effect of structural changes on absorption
  17. 17. Visible Spectroscopy Remember: ROY G. BIV violate , indigo, blue, green, yellow, orange, redRange: 400nm - 700nm
  18. 18. Absorption in visible regionThink of the flame test in high school chemistry
  19. 19. AAMC: Must know about mass spec.•Mass-to-charge ratio (m/z)•Molecular ion peak
  20. 20. Mass spectroscopy Used to identify chemicalformula and molecular mass,by bombarding with electrons and fragmenting sample.
  21. 21. m/z =18 (H20)+ since O + H + H = 16 + 1 + 1 = 18 amum/z=17 (HO)+ since O + H = 16 + 1 = 17 amum/z=16 (O)+ since O = 16 amum/z=1 (H)+ since H = 1 amu
  22. 22. Any questions? Comments? Suggestions?
  23. 23. Questions 1A chemist isolated a compound of interest. H e needs to verify that his product is a conjugated diene. What spectroscopic method can he use?a) NMR spectroscopyb) IR spectroscopyc) Ultraviolet spectroscopyd) Mass Spectroscopy
  24. 24. Questions 1A chemist isolated a compound of interest. H e needs to verify that his product is a conjugated diene. What spectroscopic method can he use?a) NMR spectroscopyb) IR spectroscopyc) Ultraviolet spectroscopyd) Mass Spectroscopy
  25. 25. Question 2A stretch at 3400 cm-1 in an IR spectrum indicates the presence of what functional group?a) Alkyneb) Ketonec) Alkened) Alcohol
  26. 26. Question 2A stretch at 3400 cm-1 in an IR spectrum indicates the presence of what functional group?a) Alkynesb) Ketonec) Alkenesd) Alcohol
  27. 27. Question 3 13Which peak is referred to as the parental peak?a) 44b) 87c) 72d) 13
  28. 28. Question 3 13Which peak is referred to as the parental peak?a) 44b) 87c) 72d) 13
  29. 29. References• Dr. Flowers MCAT• Google Images: IR spectroscopy, visible spectroscopy,• http://mcat-review.org/molecular-structure- spectra.php• http://www.users.muohio.edu/gungbw/functi onalgroups.html• http://chemicalinstrumentation.weebly.com/ir -spectrometry.html
  30. 30. Answers: Visible spectrum passage28. D29. C30. C31. D32. B33. A

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