Carboxylic acids show a strong, wide band for the OH stretch. Unlike the OH stretch band observed in alcohols, the carboxylic acid OH stretch appears as a very broad band in the region 3300-2500 cm-1, centered at about 3000 cm-1. This is in the same region as the CH stretching bands of both alkyl and aromatic groups. Thus a carboxylic acid shows a somewhat "messy" absorption pattern in the region 3300-2500 cm-1, with the broad OH band superimposed on the sharp CH stretching bands. The reason that the OH stretch band of carboxylic acids is so broad is becase carboxylic acids usually exist as hydrogen-bonded dimers.
The carbonyl stretch C=O of a carboxylic acid appears as an intense band from 1760-1690 cm-1. The exact position of this broad band depends on whether the carboxylic acid is saturated or unsaturated, dimerized, or has internal hydrogen bonding. See also:
The CO stretch appears in the region 1320-1210 cm-1, and the OH bend is in the region 1440-1395 cm-1 and 950-910 cm-1, although the 1440-1395 band may not be distinguishable from CH bending bands in the same region.