The $\mathrm{IUPAC}$ name for ${\mathrm{CH}}_3\mathrm{CO}-{\mathrm{CH}}_3$ is

$\stackrel{1}{{\mathrm{CH}}_3}-\stackrel{2}{\mathrm{CO}}-\stackrel{3}{{\mathrm{CH}}_3}$ Ketones are named by adding the suffix '-one' in place of '-e' of alkane. Thus IUPAC name is propanone.