Chapter 16: Isomerism

Isomerism is a fundamental concept in chemistry that refers to the existence of two or more substances with the same molecular formula, but with different physical and chemical properties. This is because these substances have different arrangements of atoms or groups of atoms. In the context of preparing for the Enem, it is crucial to understand isomerism, as it is often addressed in test questions.

Types of Isomerism

Isomerism can be classified into two main types: plane isomerism and spatial isomerism.

Flat Isomerism

In planar isomerism, the isomers differ in the way the atoms are connected to each other. There are five types of plane isomerism: chain isomerism, position isomerism, function isomerism, compensating isomerism or tautomerism, and dynamic isomerism or metamerism.

1. Chain Isomerism: Isomers have the same molecular formula but different chain structures. For example, butane and methylpropane are chain isomers.

2. Position Isomerism: Isomers have the same molecular formula and the same chain, but differ in the position of a functional group, an unsaturation or an atom. For example, but-1-ene and but-2-ene are positional isomers.

3. Function Isomerism: Isomers have the same molecular formula but different functional groups. For example, ethyl alcohol and methyl ether are function isomers.

4. Compensation Isomerism or Tautomerism: This is a special case of function isomerism, where one isomer can quickly convert into another under certain conditions. For example, ketone and enol are tautomers.

5. Dynamic Isomerism or Metamerism: In this case, the isomers differ in the position of an atom or group of displaceable atoms in the chain. For example, ethers are typical examples of metamers.

Spatial Isomerism

In spatial isomerism, isomers have the same molecular formula and the same bonding sequence of atoms, but differ in the spatial orientation of the atoms or groups of atoms. There are two types of spatial isomerism: geometric or cis-trans isomerism and optical isomerism.

1. Geometric or Cis-Trans Isomerism: Isomers have the same molecular formula and the same bonding sequence of atoms, but differ in the spatial orientation of groups of atoms around a double bond or a bonding system . For example, 2-butene has two geometric isomers: cis-2-butene and trans-2-butene.

2. Optical Isomerism: Isomers have the same molecular formula and the same bonding sequence of atoms, but differ in the way they interact with polarized light. This is because they have an asymmetric carbon atom, also known as a chiral carbon. For example, the glyceraldehyde molecule has two optical isomers: glyceraldehyde D and glyceraldehyde L.

In summary, isomerism is an important concept that helps to understand the diversity of chemical compounds with the same molecular formula. Understanding isomerism is crucial for solving problems and carrying out experiments in chemistry, and is a topic frequently covered in Enem.