异构 - 定义，类型，结构，例子

有机化学是一门涉及共价键中含有碳的有机分子的结构、特征和相互作用的化学学科。它们的结构式是通过研究它们的结构来确定的。研究物理和化学质量以及化学反应性，以更好地了解它们的行为。天然产物、药物和聚合物的化学合成，以及单个有机分子的实验室和理论（计算机）研究，都是有机过程研究的一部分。

碳氢化合物（仅包含碳和氢的化合物）和基于碳但还包括其他元素的化合物，例如氧、氮、硫、磷（在许多生化产品中发现）和卤素，是有机化学研究的物质之一。碳-金属键合的研究被称为有机金属化学。

异构

One of the most essential features of organic molecules is their propensity to show isomerism. Two or more compounds with the same molecular formula but different physical and chemical properties are known as isomers. Isomerism is the term for this phenomenon.

异构的类型

异构可以分为两类：

1. 结构或组成异构
2. 立体异构。

结构异构或宪法异构

The constitution of a molecule refers to the quantity, kind, and connection of its atoms. The structural isomers or constitutional isomers differ in the connection of their atoms, and this phenomenon is known as constitutional isomerism or structural isomerism.

因为它们具有相同的分子式，乙醇和二甲醚是异构体。 C ₂ H ₆ O。由于每种化学物质中的原子键合方式不同，因此它们是结构异构体。以下是各种形式的结构异构的一些例子：

• 链异构
• 位置异构
• 功能异构
• 同色异谱
• 互变异构
• 环链异构

链异构

Chain isomers are isomeric substances that differ solely in the arrangement of carbon atoms in the base chain, and chain isomerism is isomerism between them. The carbon atom chain or skeleton differs amongst isomers of this type. 

碳原子可以排列成直链或支链。最多包含三个碳原子的分子中不存在链异构现象，因为它们是连续链，没有机会分支。具有四个或更多碳原子的化合物证明了这一点。

• 烷烃中的链异构：含有四个或更多碳原子的烷烃。例如，两种链异构体由化学式C ₄ H ₁₀表示。

• 烯烃中的链异构：写烯烃的链异构体时，不应修改双键的位置。例如，两个链异构体由化学式C ₄ H ₈表示。

• 炔烃中的链异构：链异构发生在炔烃中，炔烃是具有五个或更多碳原子的化合物。这两种链异构体由化学式C ₅ H ₈表示。

位置异构

Position isomerization is a phenomenon that occurs when two or more compounds differ in the position of a component atom or functional group on the carbon skeleton.

例如，C ₃ H ₈ O 由两种醇组成：

功能异构

Two or more molecules with the same chemical formula but distinct functional groups are called functional isomers. Functional isomerism is the term for this occurrence. 

例如，化学式 C ₃ H ₆ O 表示醛和酮：

同色异谱

Metamers are molecules that have the same chemical formula but differ in atomic or group locations on both sides of bridge functional groups. Metamers are distinguished by the nature of the alkyl groups surrounding a certain functional group. 

结果，他们有联系。例如，化学式 C ₄ H ₁₀ O 包含三种异构异构醚。

互变异构

Tautomers are functional isomers that exist in dynamic equilibrium at the same time. The most prevalent kind is keto-enol tautomerism, which is caused by the 1,3 movement of the hydrogen atom from carbon to oxygen and vice versa.

例如，

醛或酮中的互变异构需要存在参与 1,3-迁移的氢。在缺乏a-氢的情况下，互变异构不存在。例如，丙酮、乙醛和苯乙酮可能由于 a-氢的存在而显示互变异构，而苯甲醛和二苯甲酮由于不存在 a-氢而不会显示。

环链异构

Ring chain isomerism is structural isomerism that differs from the other structural isomers discussed previously. It is present in isomeric open-chain and cyclic molecules. Compounds with the same chemical formula but open-chain or cyclic structures are known as ring chain isomers. And this phenomenon is known as ring chain isomerism.

环链异构体由化学式C ₃ H ₆表示。

立体异构

Stereoisomers are compounds that have the same chemical and structural formulae but differ in the relative arrangement of the atoms or groups in space, a phenomenon known as stereoisomerism.

立体异构可分为两类：

1. 构象异构体：构象异构体是在分子内具有不同原子相对位置的立体异构体，可以通过围绕sigma链旋转相互转换。换句话说，不需要为了使这些异构体相互转化而破坏和重新形成共价键。
2. 构型异构体：只能通过破坏和重建共价键而不是围绕σ键旋转的立体异构体称为构型异构体。几何异构和光学异构是构型异构的两种类型。
   • 几何异构体或顺反异构体：由围绕分子中的链接的受限旋转产生的异构体称为几何异构体或顺反异构体。多种物质表现出几何异构现象，其特点如下：
     • C=C、C=N、N=N是具有双键的化合物的例子。
     • 环状分子，包括同环、杂环和稠环系统。
     • 防止围绕单键旋转的空间位阻化合物。以联苯为例。
   • 光学异构：某些化学物质可以以两种互不相容的立体异构形式存在。尽管原子排列发生变化，但这些异构体具有相同的物理性质，如熔点、沸点、折射率、密度、溶解度等。它们的大部分化学相互作用也相似。它们仅在平面偏振光方面的行为不同。一个将其向右旋转，而另一个将其向左旋转，但角度相同。光学异构体是一对具有相同光学性质的化学物质。光学异构体是两种化合物，它们包含相同数量和类型的原子、键和原子的空间构型，但彼此不是可叠加的镜像。对映异构体是彼此不可叠加的镜面反射的异构体。

示例问题

问题1：什么是异构？

回答：

Two or more compounds with the same molecular formula but distinct physical and chemical properties are known as isomers. Isomerism is the term for this phenomenon.

问题2：异构的类型有哪些？

回答

Isomerism can be divided into two categories. Stereoisomerism and structural isomerism are the two types.

• Structural isomerism
  1. Chain isomerism
  2. Positional isomerism
  3. Functional isomerism
  4. Metamerism
  5. Tautomerism
  6. Ring chain isomerism
• Stereoisomerism
  1. Constitutional isomerism
  2. Conformational isomerism
     • Optical isomerism
     • Geometrical isomerism

问题3：什么是环链异构？

回答：

Compounds with the same chemical formula but open-chain or cyclic structures are known as ring chain isomers. Ring-chain isomerism is the term for this phenomena.

For example,  the molecular formula C₃H₆ represents the ring chain isomers

问题4：什么是结构异构？

回答：

The structural isomers or constitutional isomers differ in the connection of their atoms, and this phenomenon is known as constitutional isomerism. There are six types of structural isomerism.

1. Chain isomerism
2. Positional isomerism
3. Functional isomerism
4. Metamerism
5. Tautomerism
6. Ring chain isomerism

问题 5：什么是位置异构？

回答：

Position isomers are two or more compounds that differ in the position of a constituent atom or functional group on the carbon skeleton, and the phenomenon is known as position.

 For example,C₃H₈O, represents two alcohols: