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Examining IR spectra for the presence of OH

Infrared (IR) spectrometry can serve as a simple method to gather information on the presence of OH. Characteristic OH absorptions occur around the ranges of 3700-3200 cm-1 (OH stretching) and 1200-1000 cm-1 (OH bending). In the case of hydrogen-bonded OH, the band in the region 3700-3200 cm-1 generally appears broad and sometimes can go unnoticed.

Below is the IR spectrum for butanoic acid. The presence of the two bands at 3582 cm-1 and 1150 cm-1 suggest that an OH group is present.

IRforOH_Str_Nov172008 IRforOH_Spec_Nov172008

TIP: An incorrect interpretation may occur for samples that contain impurities with OH groups, for example, water.

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