Chris Schaller

Chem 235 and Chem 236 - Organic Chemistry

Infrared Spectroscopy


Red Herrings: Overtones and Water

There are some practical problems that can make IR interpretation in real life more difficult. Being aware of these problems may make you double-check your suspicions:

 water in the sample. Since water contains O-H bonds, water in a sample will make it appear as if the compound contains O-H bonds. There are experimental techniques for removing water from a sample but they must be done carefully.

 overtones in a spectrum. Overtones are absorptions occurring at different multiples of the normal frequency. Strong overtones of carbonyl peaks often occur at about twice the normal wavenumber. A large peak at 1750 cm-1 might be accompanied by a smaller peak at 3500 cm-1, and could be confused with an O-H peak.



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