HOOC−COOH \mathrm {HOOC-COOH}HOOC−COOH
HOH2C−CH2OH\mathrm{HOH}_{2} \mathrm{C}-\mathrm{CH}_{2} \mathrm{OH}HOH2C−CH2OH
HCHO \mathrm {HCHO}HCHO
OHC−CHO\mathrm {OHC-CHO}OHC−CHO