File:Chapter-20 Infrared spectroscopy (Identifying Compounds or ligands) pp 161-173.pdf

An IR spectrum can be visualized in a graph of infrared light absorbance (or transmittance) on the vertical axis (y axis) vs. frequency or wavelength on the horizontal axis (x axis). Typical units of frequency used in IR spectra are reciprocal centimeters (sometimes called wave numbers), with the symbol cm−1. The infrared portion of the electromagnetic spectrum is usually divided into three regions; the near-, mid- and far- infrared. Among these regions, the mid-infrared, approximately 4000–400cm−1 (2.5–25 μm) may be used to study the presence of different moieties or groups present in certain compounds or ligands.