Group frequency and fingerprint regions of the mid-infrared spectrum These types of infrared bands are called group frequencies because they tell us about the presence or absence of specific functional groups in a sample. This makes these bands diagnostic markers for the presence of a functional group in a sample. For example, C-H stretching vibrations usually appear between 32cm -1 and carbonyl(C=O) stretching vibrations usually appear between 18cm -1.
\)Īn important observation made by early researchers is that many functional group absorb infrared radiation at about the same wavenumber, regardless of the structure of the rest of the molecule.
