HCOOH\mathrm{HCOOH}HCOOH
CH3COOH\mathrm{CH}_{3} \mathrm{COOH}CH3COOH
(CH3CO)2O\left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O}(CH3CO)2O
CH3COCH3\mathrm{CH}_{3} \mathrm{COCH}_{3}CH3COCH3