Benzoic acid has an IR spectroscopy with large peaks present in the 2500 to 3300 centimeter^-1 region, in the 1680 to 1750 region, in the 1300 region and in the 900 to 1100 region. All of these absorptions coincide with functional groups present in the compound.
The peak noted in the 2500 to 3300 centimeter ^-1 region is indicative of an OH group present in benzoic acid. The absorption between 1680 and 1750 is indicative of a carbon oxygen double bond present in benzoic acid. The absorption present around 1300 is also indicative of an OH group, and it correlates with the peak between 2500 and 3300. Finally, the absorption peak at 900 to 1100 is indicative of the benzene ring present in the benzoic acid compound.