CH3CH2CH2CO

CH3CH2CH2CO commonly denotes the butanoyl (butyryl) acyl fragment, more precisely written CH3CH2CH2C(=O)–. It is the four‑carbon acyl group derived from removal of the hydroxyl hydrogen from butanoic (butyric) acid or from cleavage of a C–O bond in a carbonyl derivative. The group is often encountered as part of larger molecules (for example, butanoyl chloride, esters, amides or thioesters such as butyryl‑CoA) rather than as an isolated neutral species.

Chemically, the carbonyl carbon in the butanoyl group is electrophilic due to resonance and polarization of the C=O bond, making it susceptible to nucleophilic acyl substitution and addition reactions. In radical or gas‑phase chemistry the corresponding acyl radical (CH3CH2CH2CO•) can form and participates in combustion, pyrolysis and certain organic synthesis pathways. Spectroscopically, carbonyl-containing derivatives display a strong IR stretch near 1700 cm−1 and a 13C NMR carbonyl signal typically downfield around 170–180 ppm, depending on substitution and solvent.

Butanoyl-containing structures appear in synthetic organic chemistry, biochemical intermediates (notably butyryl‑CoA), pharmaceuticals and in flavor and fragrance compounds. The term “butyryl” is commonly used in biochemistry and industry, while “butanoyl” is the preferred IUPAC name for the acyl group.