Infra red spectra can be used to deduce the functional groups and hence the structure of an organic compound. The vertical axis is % transmittance and the horizontal axis is wavenumber (cm-1) which is 1/wavelength. At specific wavenumbers there are troughs (absorption peaks) with different intensities or transmittance values.The fingerprint region is from 1500 to 500 cm-1. Most of the absorptions result from bending vibrations and are characteristic of the molecule.The -OH group of an alcohol shows a broad absorption peak between 3200 and 3550 cm-1. (The O-H of a carboxylic acid gives a very broad absorption from 2500 to 3300 cm-1.)