CH3CO2H\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}CH3CO2H
HCO2H\mathrm{HCO}_{2} \mathrm{H}HCO2H
(CH3CO)2O\left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O}(CH3CO)2O
CH3CHO\mathrm{CH}_{3} \mathrm{CHO}CH3CHO