CH3(CH2)3−COOH\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3}-\mathrm{COOH}CH3(CH2)3−COOH
CH3(CH2)2−COOH\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2}-\mathrm{COOH}CH3(CH2)2−COOH
CH3−COOH\mathrm{CH}_{3}-\mathrm{COOH}CH3−COOH
HOOC−COOH\mathrm{HOOC}-\mathrm{COOH}HOOC−COOH
