Acetone, $\mathrm{CH}{}_3\mathrm{COCH}{}_3$, and prop-1-en-2-ol, $\mathrm{CH}{}_2=\mathrm{C}(\mathrm{OH})\mathrm{CH}{}_3$, are best described as

The two have the same formula $\mathrm{C}{}_3\mathrm{H}{}_6\mathrm{O}$ and differ in functional group (ketone versus enol), interconverting by a hydrogen shift. They are tautomers (functional isomers in rapid equilibrium); the keto form is the one that predominates at room temperature.