Ketene

Ketene is the compound $\mathrm{C}{\mathrm{H}}_2=\mathrm{C}=\mathrm{O}$, also called ethenone. More generally, ketenes contain the cumulative $\mathrm{C}=\mathrm{C}=\mathrm{O}$ unit.^[ref] Adjacent double bonds make this a different functional group from an ordinary isolated alkene or ketone.

Attack by a suitable nucleophile at the electrophilic carbon can convert a ketene into a carboxylic-acid derivative; addition of water, for example, gives an acid. Substitution around the terminal carbon affects both reaction selectivity and competing pathways. The displayed parent formula should not be confused with every substituted member of the ketene class.