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SURVEY OF SPECTRA

HALIDES. CH Out -of-Plane Bending. Making Decisions on a Functional Group / What you need to know. SURVEY OF SPECTRA. 2.5 . 4. 5. 5.5. 6.1. 6.5. 15.4. 4000. 2500. 2000. 1800. 1650. 1550. 650. Typical Infrared Absorption Regions. C-Cl. WAVELENGTH ( m m). C-Cl. C=O.

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SURVEY OF SPECTRA

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  1. HALIDES CH Out -of-Plane Bending Making Decisions on a Functional Group / What you need to know SURVEY OF SPECTRA

  2. 2.5 4 5 5.5 6.1 6.5 15.4 4000 2500 2000 1800 1650 1550 650 Typical Infrared AbsorptionRegions C-Cl WAVELENGTH (mm) C-Cl C=O C=N O-H C-H C N Very few bands C-O C=C N-H C C C-N X=C=Y C-C * N=O N=O (C,O,N,S) FREQUENCY (cm-1)

  3. The C-X stretching region • C-Cl 785 to 540 cm-1, often hard to find amongst the fingerprint bands!! • C-Br and C-I appear outside the useful range of infrared spectroscopy. • C-F bonds can be found easily, but are not that common.

  4. Often used as a solvent for IR spectra. When it is used, spectra show C-Cl absorptions. Carbon Tetrachloride C-Cl

  5. benzene ring combination bands Chlorobenzene oops benzene C=C C-Cl

  6. =C-H OUT OF PLANE BENDING

  7. OUT-OF-PLANE BENDING (OOPS) PLANE above H ALKENES H H below also with H BENZENES

  8. m 10 11 12 13 14 15 ALKENES s s Monosubstituted Disubstituted cis-1,2- s trans-1,2- s 1,1- s Trisubstituted m =C-H OUT OF PLANE BENDING Tetrasubstituted 1000 900 800 700 cm-1

  9. m 10 11 12 13 14 15 BENZENES Monosubstituted s s Disubstituted s ortho m s s meta para s RING H’s Trisubstituted OOPS m s 1,2,4 1,2,3 s m 1,3,5 s m combination bands 1000 900 800 700 cm-1

  10. YOU DO NOT NEED TO MEMORIZE THE ALKENE AND AROMATIC OOP ABSORPTION CHARTS ! If they are needed to solve a problem on an exam, I will provide them.

  11. BACKGROUND SPECTRUM MODERN FT-IR INSTRUMENTS SUBTRACT THE “BACKGROUND”

  12. “BACKGROUND” Carbon Dioxide and Water H-O-H H-O-H O=C=O

  13. MAKING DECISIONS DECISION FLOW CHART Tables 11-8 and 11-9

  14. YES C=O present ? YES anhydride 2 C=O Peaks acid OH present ? amide NH present ? ester C-O present ? aldehyde CHO present ? ketone NO

  15. NO C=O present ? YES alcohol OH present ? NH present ? amine C-O present ? ether = nitrile C=N present ? = alkyne C=C present ? alkene C=C present ? (benzene ?) aromatic NO2 present ? nitro cpds C-X present ? halides

  16. YES NO C=O present ? YES YES anhydride 2 C=O Peaks alcohol OH present ? acid OH present ? NH present ? amine amide NH present ? C-O present ? ether = ester C-O present ? nitrile C=N present ? = aldehyde CHO present ? alkyne C=C present ? alkene C=C present ? ketone NO (benzene ?) aromatic NO2 present ? nitro cpds C-X present ? halides

  17. GUIDELINES DECISION FLOW CHART Tables 11-8 and 11-9

  18. How to Use an Infrared Spectrum Molecular formula: 1) calculate index of hydrogen deficiency 2) Check for carbonyl: note any shift from 1715 cm-1 Check for O-H, N-H 3) Check for triple bonds 4) Check for C=C, benzene rings 5)

  19. How to Use an Infrared Spectrum CONTINUED Look below 1550 cm-1; check for C-O and 6) nitro Go back over spectrum for refinements; check the C-H region for aldehydes and for peaks above 3000 cm-1 7) (alkenes and terminal alkynes)

  20. FINAL SUMMARY WHERE YOU SHOULD HAVE A SECURE GRASP WHEN READING INFRARED SPECTRA

  21. THE MINIMUM YOU NEED TO KNOW EXPANDED CH 3000 BASE VALUES OH 3600 NH 3400 CH 3000 C N 2250 C C 2150 C=O 1715 C=C 1650 C-O 1100 3300 3100 2900 2850 2750 C-H =C-H -C-H -CHO CH2 and CH3 bend :1465and1365 1800 1735 1725 1715 1710 1690 aldehyde acid acid chloride ester amide ketone anhydride : 1810 and 1760 EXPANDED C=O benzene C=C : between1400and1600 Know also the effects of H-bonding, conjugation and ring size.

  22. WHERE CAN I GET MORE SPECTRA FOR PRACTICE?

  23. ADDITIONAL SOURCES OF INFRARED SPECTRA In the back of your laboratory book is an index of all the infrared spectra in the book. 1) Pavia, Lampman, Kriz and Engel, Introduction to Organic Laboratory Techniques, Saunders College Publishing In the Chemistry Department computer lab in the ChemApps/Spectroscopy folder are two programs called “Spectrabook I” and “Spectrabook II”. 2) These programs can display the IR spectra of many compounds and the selection lists can be grouped by functional group. When you click on a peak with the mouse the group of atoms resposible for the absorption is shown.

  24. There are several web sites that have spectra, including: 3) http://www.dq.fct.unl.pt/qoa/jas/ir.html http://www.aist.go.jp/RIODB/SDBS/menu-e.html http://webbook.nist.gov/chemistry/ http://www.chem.ucla.edu/~webnmr/index.html http://www.nd.edu/~smithgrp/structure/workbook.html Books on the subject of spectroscopy, such as: 4) D.L.Pavia, G.M.Lampman, and G.S.Kriz, Introduction to Spectroscopy, 3rd ed., Harcourt. You will probably be able to find some local WWU students who have this book (it is used in Chem 454 and 455) - but it is more advanced than you probably need.

  25. The program “IR Tutor” can be found in the ChemApps folder in the Chemistry Department computer lab. 5) This program contains a number of sample spectra and the vibrations responsible for each peak can be viewed as an animation.

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