Downloaded 58 times
Absorption spectroscopy
- 1. Absorption and Mass Spectroscopy Presenter: Cynthia Echefu
- 2. Absorption Spectroscopy Infrared (IR)- Used to determine functional groups (molecular vibration, which includes bending, stretching and rotation) Ultraviolet- Used to identify conjugated double bonds Visible – sequence of light color the eye can see
- 3. AAMC: Must knowabout IR • intramolecular vibrations and rotations • recognizing common characteristic group absorptions, fingerprint region
- 4. Infrared spectrum violate ,indigo, blue, green, yellow, orange, red
- 5. Vibrations: bonds canstretch, 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. Wave number (1/ƛ) (cm-1) 4000 500 3500 3000 2500 2000 1500 1000
- 7.
- 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. 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.
- 12. 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- 1750 Aliphatic 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)
- 14. Must Know Alcohol (broad) Acid (sharp) Ketone (sharp) Amine (slightly sharp) Alkyne (C-H)(sharp)
- 15. AAMC: Must knowabout UV • π -electron and nonbonding electron transitions • conjugated systems
- 16. Ultraviolet Spectroscopy Electronsabsorption UV energy, which causes the electrons to transition from a low energy level (ground state) to a higher energy level (excited state).
- 17. Bonding, non-bonding andanti-bonding • Electron excitation
- 18. 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
- 19. AAMC: Must knowabout visible • absorption in visible region yielding complementary color • effect of structural changes on absorption
- 20. Visible Spectroscopy Remember: ROY G. BIV violate , indigo, blue, green, yellow, orange, red Range: 400nm - 700nm
- 21. Absorption in visibleregion Think of the flame test in high school chemistry
- 22. AAMC: Must knowabout mass spec. •Mass-to-charge ratio (m/z) •Molecular ion peak
- 23. Mass spectroscopy Usedto identify chemical formula and molecular mass, by bombarding with electrons and fragmenting sample.
- 25. m/z =18 (H20)+since O + H + H = 16 + 1 + 1 = 18 amu m/z=17 (HO)+ since O + H = 16 + 1 = 17 amu m/z=16 (O)+ since O = 16 amu m/z=1 (H)+ since H = 1 amu
- 26. Any questions? Comments? Suggestions?
- 27. Questions 1 A chemistisolated a compound of interest. H e needs to verify that his product is a conjugated diene. What spectroscopic method can he use? a) NMR spectroscopy b) IR spectroscopy c) Ultraviolet spectroscopy d) Mass Spectroscopy
- 28. Questions 1 A chemistisolated a compound of interest. H e needs to verify that his product is a conjugated diene. What spectroscopic method can he use? a) NMR spectroscopy b) IR spectroscopy c) Ultraviolet spectroscopy d) Mass Spectroscopy
- 29. Question 2 A stretchat 3400 cm-1 in an IR spectrum indicates the presence of what functional group? a) Alkyne b) Ketone c) Alkene d) Alcohol
- 30. Question 2 A stretchat 3400 cm-1 in an IR spectrum indicates the presence of what functional group? a) Alkynes b) Ketone c) Alkenes d) Alcohol
- 31. Question 3 13 Which peak is referred to as the parental peak? a) 44 b) 87 c) 72 d) 13
- 32. Question 3 13 Which peak is referred to as the parental peak? a) 44 b) 87 c) 72 d) 13
- 33. References • Dr. FlowersMCAT • 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
- 34. Answers: Visible spectrumpassage 28. D 29. C 30. C 31. D 32. B 33. A