The compound CH3-CO-CH3 has three carbon atoms and a ketone functional group (-CO-) in the middle. The IUPAC naming conventions: 'Prop-' indicates three carbon atoms, '-an-' indicates single bonds between carbon atoms in the main chain, and '-one' is the suffix for a ketone. Thus, its IUPAC name is Propanone (common name: acetone). Propanal has an aldehyde group, Propanoic acid has a carboxylic acid group, and Ethanal has two carbon atoms.