Infrared and Raman Spectra

Abstract

The infrared spectra of organic compounds are associated with transitions between vibrational energy levels. Molecular vibrations may be detected and measured either in an infrared spectrum or indirectly in a Raman spectrum. The most useful vibrations, from the point of view of the organic chemist, occur in the narrower range of 3.5–16 μm (1 μm = 10⁻⁶ m). The position of an absorption band in the spectrum may be expressed in microns (μm), but standard practice uses a frequency scale in the form of wavenumbers, which are the reciprocals of the wavelength, cm⁻¹. The useful range of the infrared for an organic chemist is between 4000 cm⁻¹ at the high-frequency end and 600 cm⁻¹ at the low-frequency end.