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Infrared Radiation: Molecular Vibrations

Infrared Radiation: Molecular Vibrations . Electromagnetic Radiation: Light, Energy, Heat IR Tutor: http://chemistry.beloit.edu/Warming/pages/infrared.html. What do the sun’s energy, a molecule’s shape and a TV remote have to do with greenhouse gases?.

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Infrared Radiation: Molecular Vibrations

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  1. Infrared Radiation: Molecular Vibrations

  2. Electromagnetic Radiation: Light, Energy, HeatIR Tutor:http://chemistry.beloit.edu/Warming/pages/infrared.html

  3. What do the sun’s energy, a molecule’s shape and a TV remote have to do with greenhouse gases? http://chemistry.beloit.edu/Stars/EMSpectrum/index.html

  4. Infrared Absorbance

  5. Infrared Absorbance TV Remote

  6. Infrared Absorbance Sample TV Remote

  7. Infrared Absorbance & Molecular Vibrations for CCl4Stretching & Bending

  8. Infrared Spectroscopy

  9. Infrared Absorbance

  10. IR- Empirical Comparisons Identifying functional groups in organic molecules

  11. Infrared Spectroscopy Region of infrared that is most useful lies between2.5-16 mm (4000-625 cm-1) depends on transitions between vibrational energy states Stretching: higher energy / higher wave number (cm-1) Bending: lower energy / lower wave number (cm-1)

  12. A bond must have a dipole or an induced dipole in order to have an absorbance in the IR spectrum. When the bond stretches, the increasing distance between the atoms increases the dipole moment. Therefore, the greater the dipole, the more intense the absorption. (i.e., The greater the molar extinction coefficient () in Beer’s law, A = bc.

  13. Analyzing Structure: Functions & Infrared Spectra The molecular formula is a critical piece of information, which limits the functional possibilities. The presence & absence of absorption bands must be considered in identifying a possible structure in IR spectroscopy. Empiricism is critical to successful identification. NOTE: Bonds which lack dipole moments are not detected.

  14. Structural/Functional Components

  15. An Infrared Spectrum The peaks are quantized absorption bands corresponding to molecular stretching and bending vibrations

  16. The fingerprint region The functional group stretching region

  17. Infrared Absorption Frequencies Structural unit Frequency, cm-1 Stretching vibrations (single bonds) O—H (alcohols) 3200-3600 O—H (carboxylic acids) 3000-3100 First examine the absorption bands in the vicinity of 4000-3000 cm–1

  18. Infrared Absorption Frequencies Structural unit Frequency, cm-1 Stretching vibrations (single bonds) sp C—H 3310-3320 sp2 C—H 3000-3100 sp3 C—H 2850-2950 sp2 C—O 1200 sp3 C—O 1025-1200

  19. C O Infrared Absorption Frequencies Structural unit Frequency, cm-1 Stretching vibrations (carbonyl groups) Aldehydes and ketones 1710-1750 Carboxylic acids 1700-1725 Acid anhydrides 1800-1850 and 1740-1790 Esters 1730-1750 Amides 1680-1700

  20. Cyclic aliphatic ketone

  21. Mono substituted aromatic methyl ketone

  22. Mono substituted aromatic ketone

  23. Aliphatic ester I

  24. Aliphatic ester II

  25. Aliphatic ester III

  26. Mono substituted aromatic ester

  27. Mono substituted aromatic conjugated ester

  28. Infrared Absorption Frequencies Structural unit Frequency, cm-1 Stretching vibrations (single bonds) sp2 C—O 1200 sp3 C—O 1025-1200

  29. Dihexyl Ether ~1100 cm-1 1025-1200 cm-1

  30. Carboxylic Acid ~1200 cm-1

  31. Distinctive Stretch of C–H Bond in an Aldehyde (the “waggle” vibration)

  32. Aliphatic aldehyde

  33. Mono-substituted aromatic aldehyde

  34. Mono substituted aromatic ester

  35. Para di-substituted aromatic ether & aldehyde

  36. Infrared SpectroscopyCommon Functional Groups Handout

  37. Acetate Esters: Smell / Pheromones http://chemconnections.org/COT/COT-chemcomm-eg.html Pheromone Synthesishttp://chemconnections.org/organic/chem226/Labs/acetate%20syn/Z-selective%20Insect%20Pheromones%20syn.pdf http://www.learner.org/resources/series61.html [20:40-23:51]

  38. Infrared SpectroscopyCommon Functional GroupsQuestions

  39. Question #1 C7H6O Identify the compound from the IR above. • benzyl alcohol • 2,4,6-cycloheptaheptatrien-1-one • acetophenone • benzaldehyde • phenylacetic acid

  40. Question #2 C10H12O Identify the compound from the IR above. • 2,4,5-trimethylbenzaldehyde • p-allylanisole • 2-allyl-4methylphenol • 1-phenyl-2-butanone

  41. Question #3 C3H4O Identify the compound from the IR above. • cyclopropanone • propynol • acrylaldehyde • propenoic acid

  42. Question #4 C8H8O2 Identify the compound from the IR above. • methylbenzoate • o-hydroxyacetophenone • o-toluic acid • p-anisaldehyde (p-methoxybenzaldehyde)

  43. Question #5 C8H8O2 Identify the compound from the IR above. • benzylformate • o-hydroxyacetophenone • 2-methoxytropone • p-toluic acid • o-anisaldehyde (p-methoxybenzaldehyde)

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