Constitutional isomers, also called structural isomers, are isomers that differ in their connectivity, that is, in how the atoms are bonded together. They matter as the most basic kind of isomerism, in which the very skeleton of the molecule changes. They take several forms, including chain isomers, positional isomers and functional-group isomers; this contrasts with stereoisomers, which share the same connectivity and differ only in spatial arrangement.

构造异构体,又称结构异构体,是指连接方式(即原子如何成键连接在一起)不同的异构体。它们是最基本的一类同分异构,其中分子的骨架本身发生改变,因而很重要。它们有多种形式,包括链异构、位置异构和官能团异构;这与连接方式相同、仅空间排列不同的立体异构体形成对照。