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Infrared Spectroscopy

Infrared Spectroscopy. Gives information about the functional groups in a molecule. Infrared Spectroscopy. region of infrared that is most useful lies between 2.5-16 m m (4000-625 cm -1 ) depends on transitions between vibrational energy states stretching bending.

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Infrared Spectroscopy

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  1. Infrared Spectroscopy Gives information about the functional groups in a molecule

  2. 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 bending

  3. Stretching Vibrations of a CH2 Group Symmetric Antisymmetric

  4. Bending Vibrations of a CH2 Group In plane In plane

  5. Bending Vibrations of a CH2 Group Out of plane Out of plane

  6. Example of infrared spectrum Transmittance (%) 100 Hexane bending C—H stretching bending bending 0 4400 3600 2800 2000 1600 1200 800 Wave number, cm-1

  7. Example of infrared spectrum Transmittance (%) 100 Hexane no peaks higher than 3000 cm-1 0 4400 3600 2800 2000 1600 1200 800 Wave number, cm-1

  8. Infrared spectrum of 1-hexene Transmittance (%) 100 C=C—H C=C CH2=C— peak higher than 3000 cm-1 0 4400 3600 2800 2000 1600 1200 800 Wave number, cm-1

  9. Table 13.4 (p 519)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

  10. C C —C C— —C N Table 13.4 (p 519)Infrared Absorption Frequencies Structural unit Frequency, cm-1 Stretching vibrations (multiple bonds) 1620-1680 2100-2200 2240-2280

  11. C O Table 13.4 (p 519)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

  12. RCH CH2 R2C CH2 cis-RCH CHR' trans-RCH CHR' R2C CHR' Table 13.4 (p 519)Infrared Absorption Frequencies Structural unit Frequency, cm-1 Bending vibrations of alkenes 910-990 890 665-730 960-980 790-840

  13. Infrared spectrum of 1-hexene Transmittance (%) 100 C=C stretch CH2=C— bend 0 4400 3600 2800 2000 1600 1200 800 Wave number, cm-1

  14. Infrared spectrum of tert-butylbenzene Transmittance (%) 100 Ar—H stretch; > 3000 monosubstituted benzene 0 4400 3600 2800 2000 1600 1200 800 Wave number, cm-1

  15. Table 13.4 (p 519)Infrared Absorption Frequencies Structural unit Frequency, cm-1 Stretching vibrations (single bonds) O—H (alcohols) 3200-3600 O—H (carboxylic acids) 3000-3100 N—H 3350-3500

  16. Infrared spectrum of 2-hexanol Transmittance (%) 100 C—H stretch O—H stretch 0 4400 3600 2800 2000 1600 1200 800 Wave number, cm-1

  17. Infrared spectrum of 2-hexanone Transmittance (%) 100 C—H stretch C=O stretch 0 4400 3600 2800 2000 1600 1200 800 Wave number, cm-1

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