Infrared Spectroscopy Gives information about the functional groups in a molecule

region of infrared that is most useful lies between  m ( cm -1 ) depends on transitions between vibrational energy states stretchingbending Infrared Spectroscopy

Stretching Vibrations of a CH 2 Group SymmetricAntisymmetric

Bending Vibrations of a CH 2 Group In plane

Bending Vibrations of a CH 2 Group Out of plane

Example of infrared spectrum Hexane Transmittance (%) Wave number, cm C—H stretching bending bending bending

Example of infrared spectrum Hexane Transmittance (%) Wave number, cm no peaks higher than 3000 cm -1

Infrared spectrum of 1-hexene Transmittance (%) Wave number, cm peak higher than 3000 cm -1 C=C—H C=C CH 2 =C—

Structural unitFrequency, cm -1 Stretching vibrations (single bonds) sp C—H sp 2 C—H sp 3 C—H sp 2 C—O1200 sp 3 C—O Table 13.4 (p 519) Infrared Absorption Frequencies

Structural unitFrequency, cm -1 Stretching vibrations (multiple bonds) Table 13.4 (p 519) Infrared Absorption Frequencies C C —CN —CC—

Structural unitFrequency, cm -1 Stretching vibrations (carbonyl groups) Aldehydes and ketones Carboxylic acids Acid anhydrides and Esters Amides Table 13.4 (p 519) Infrared Absorption Frequencies C O

Structural unitFrequency, cm -1 Bending vibrations of alkenes Table 13.4 (p 519) Infrared Absorption Frequencies CH 2 RCH R2CR2CR2CR2C CHR' cis-RCH CHR' trans-RCH CHR' R2CR2CR2CR2C

Infrared spectrum of 1-hexene Transmittance (%) Wave number, cm C=C stretch CH 2 =C— bend

Infrared spectrum of tert-butylbenzene Transmittance (%) Wave number, cm Ar—H stretch; > 3000 monosubstituted benzene

Structural unitFrequency, cm -1 Stretching vibrations (single bonds) O—H (alcohols) O—H (carboxylic acids) N—H Table 13.4 (p 519) Infrared Absorption Frequencies

Infrared spectrum of 2-hexanol Transmittance (%) Wave number, cm O—H stretch C—H stretch

Infrared spectrum of 2-hexanone Transmittance (%) Wave number, cm C=O stretch C—H stretch