HCOOH\mathrm{HCOOH}HCOOH
CH3CH2COOH\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}CH3CH2COOH
C6H5−COOH\mathrm{C}_{6} \mathrm{H}_{5}-\mathrm{COOH}C6H5−COOH
CH3−COOH\mathrm{CH}_{3}-\mathrm{COOH}CH3−COOH