IR Spectroscopy Tutorial: Carbonyl Compounds

All carbonyl compounds absorb in the region 1760-1665 cm-1 due to the stretching vibration of the C=O bond. This distinctive carbonyl band is particularly useful for diagnostic purposes because it has a characteristic high intensity and few other functional groups absorb in this region. Different carbonyl compounds absorb in narrow ranges within the general carbonyl region.

The exact wavenumber of the C=O stretch can give you clues as to whether the compound is a ketone, aldehyde, ester, or carboxylic acid; furthermore it can tell you whether it is an alpha, beta- carbonyl.

range type of compound such as:
1750-1735 cm-1 saturated aliphatic esters
1740-1720 cm-1 saturated aliphatic aldehydes
1730-1715 cm-1 α, β-unsaturated esters
1715 cm-1 saturated aliphatic ketones
1710-1665 cm-1 α, β-unsaturated aldehydes and ketones

Need a refresher on alpha-beta nomenclature of carbonyls? Click on the following link: