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
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