Isomerism

When there are two molecules that have exactly the same number of the same kinds of atoms (and thus the same formula), yet they have different chemical and physical properties, this is known as isomerism. This is mostly due to the fact that diverse structural or spatial arrangements exist. The compounds that exhibit this characteristic are referred to as isomers.

Isomerism also takes into account timing and energy. Molecules are mobile entities that go through various rotating motions that change their shape, all of which require energy. As a result, specific molecules might be identical on one timeline or set of energy circumstances while being different or isomeric on another. Finally, an isomer must be an energy minimum; it must be found in a well of energy.

Types of Isomerism

There are two primary forms of isomerism, each of which can be further divided into subgroups. Structural Isomerism and Stereoisomerism are the two primary forms.

Structural Isomerism

When two isomers have the same molecular formula but distinct structures, they are said to be structural isomers. Structural isomerism can be divided into the following categories. Let’s take them one at a time and learn about them..

Positional, functional group and chain isomerism are three forms of structural isomerism.

Chain Isomerism

Isomers differ in the arrangement of their carbon chains, which might be branched or straight, in chain isomerism.

The chemical with the molecular formula C5H12 has three isomers: n-pentane, 2-methyl butane or isopentane, and 2,2-dimethylpropane or neopentane for example.

Positional isomerism 

Isomers with the same functional groups but in different positions on the same carbon chain form positional isomerism are also known as position isomerism.

The chemical with the molecular formula C6H4Br2, which has three isomers: 1,2-dibromobenzene, 1,3-dibromobenzene, and 1,4-dibromobenzene is a good example. The position of the bromine atoms on the cyclic structure differs between these isomers.

Another example is the chemical C3H8O, which has two isomers: 1-propanol, also known as n-propyl alcohol, and 2-propanol, also known as isopropyl alcohol. The location of the hydroxyl group on the carbon chain differs between these isomers.

Functional isomerism

The term “functional isomer” refers to when two or more compounds have the same molecular formula but differ in the functional group that is present in the molecules. For example, the chemical formula C3H6O can be represented as a ketone or as an aldehyde.

The chemical with the molecular formula C2H6O has two isomers: dimethyl ether and ethanol or ethyl alcohol, each of which has a distinct functional group, an ether group, –O–, and a hydroxyl group, –OH.

Metamerism

This isomerism is caused by the presence of different alkyl chains on both sides of thelement (such as sulphur or oxygen) is surrounded by alkyl groups.e functional group.

It’s an uncommon type of isomerism that only occurs when a divalent 

C4H10O includes ethoxyethane (C2H5OC2H5) and methoxy-propane (CH3OC3H7).

Tautomerism

A tautomer is an isomer of a chemical that differs only in the position of protons and electrons.

The tautomers of most compounds coexist in equilibrium and are easily interchangeable.

It occurs as a result of a proton transfer within the molecule. 

Ring-Chain isomerism

In ring-chain isomerism, one isomer has an open-chain structure, while the other has a ring structure. They usually contain a variable number of π bonds. C3H6 isomers is an excellent example of this kind of isomerism. The isomers in the end product are propene and cyclopropane.

Stereoisomerism

Isomers and stereoisomers have the same amount and type of atoms and bonds but differ in their spatial orientation. Stereoisomers are isomers that are named after the Greek word stereos, which means “solid.”

Stereoisomerism is classified into two types: conformational isomers and configurational isomerism, with the latter separated further into optical isomerism and geometrical isomerism.

Geometric isomerism

Geometric isomerism, also known as cis-trans isomerism, arises when atoms are unable to freely rotate due to a hard structure, such as the one found in:

The stiffness of compounds having carbon-carbon, carbon-nitrogen, or nitrogen-nitrogen double bonds is attributable to the double bond; the rigidity of cyclic compounds is owing to the ring structure.examples cis-2 butene and trans 2 butene.

Optical isomerism

Optical isomerism occurs in molecules with one or more chirality centres, also known as chiral centres, such as tetrahedral atoms with four distinct ligands. A carbon, phosphorus, sulphur, or nitrogen atom can serve as the chiral centre.

Optical isomers lack a symmetry centre or plane, are mirror images of one another, and cannot be overlaid on each other. Enantiomers are named after the Greek words enántios, which means “opposite,” and meros, which means “part.”

With two exceptions, two enantiomers have identical physical and chemical properties, unlike other isomers. For example, the plane of polarisation is rotated in a clockwise direction when one of the enantiomers is present in a solution.

Ionisation isomerism

Ionisation isomers are compounds that produce distinct ions in solution despite having the same composition, and this trait is known as ionisation isomerism. Ionisation isomerism refers to compounds that produce different solutions despite having the same chemical composition.

[Co(NH3)5SO4]Br and [Co(NH3)5Br]SO4 are two examples of ionisation isomerism. 

Conclusion

Isomerism arises from the fact that the atoms in a molecular formula can be organised in multiple ways to produce compounds with varied physical and chemical properties, known as isomers. Isomerism can be classified into two types: structural isomerism and stereoisomerism, which can be further subdivided.