The ratio of mass percent of C and H of an organic compound (${\mathrm{C}}_{\mathrm{x}}{\mathrm{H}}_{\mathrm{y}}{\mathrm{O}}_{\mathrm{z}}$) is 6 : 1. If one molecule of the above compound (${\mathrm{C}}_{\mathrm{x}}{\mathrm{H}}_{\mathrm{y}}{\mathrm{O}}_{\mathrm{z}}$) contains half as much oxygen as required to burn one molecule of compound ${\mathrm{C}}_{\mathrm{x}}{\mathrm{H}}_{\mathrm{y}}$ completely to ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$. The empirical formula of the compound ${\mathrm{C}}_{\mathrm{x}}{\mathrm{H}}_{\mathrm{y}}{\mathrm{O}}_{\mathrm{z}}$ is