CH3CHO\mathrm{CH}_{3} \mathrm{CHO}CH3CHO
CH3COOH\mathrm{CH}_{3} \mathrm{COOH}CH3COOH
(CH3CO)2O\left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O}(CH3CO)2O