定义Definition
构造异构体（结构异构体）是分子式相同、但原子连接顺序不同的化合物。常见类型有碳链异构、位置异构和官能团异构。构造异构体的物理性质不同，官能团不同时化学性质也不同。
Structural (constitutional) isomers have the same molecular formula but atoms joined in a different order. The common kinds are chain, positional and functional group isomerism. They differ in physical properties, and in chemical properties too when the functional groups differ.
三种类型The three kinds
碳链异构：C₅H₁₂ 有戊烷、2-甲基丁烷和 2,2-二甲基丙烷三种。位置异构：官能团位置不同，如丁-1-醇与丁-2-醇，1-氯丙烷与 2-氯丙烷。官能团异构：官能团不同，如 C₂H₆O 的乙醇与甲醚，C₃H₆O 的丙醛与丙酮。
Chain isomers: C₅H₁₂ exists as pentane, 2-methylbutane and 2,2-dimethylpropane. Positional isomers: the functional group is in a different place, as in butan-1-ol and butan-2-ol, or 1-chloropropane and 2-chloropropane. Functional group isomers: different groups, as in ethanol and methoxymethane (C₂H₆O), or propanal and propanone (C₃H₆O).
异构体数目增长很快Numbers grow quickly
烷烃的构造异构体数：C₄H₁₀ 2 种，C₅H₁₂ 3 种，C₆H₁₄ 5 种，C₇H₁₆ 9 种，C₁₀H₂₂ 75 种。
Numbers of structural isomers of alkanes: C₄H₁₀ 2, C₅H₁₂ 3, C₆H₁₄ 5, C₇H₁₆ 9, C₁₀H₂₂ 75.