羧酸有2种CH3CH2CH2COOH 正丁酸(CH3)2CHCOOH 异丁酸（或2-甲基丙酸）酯有4种HCOOCH2CH2CH3 甲酸正丙酯HCOOCH(CH3)2 甲酸异丙酯CH3COOCH2CH3 乙酸乙酯CH3CH2COOCH3 丙酸甲酯
CH3CH2COOCH3CH3COOCH2CH3HCOOCH2CH2CH3HCOOCH(CH3)2 （有支链）
