What is Meant by Isomerism - TopperLearning Blog

What is Meant by Isomerism?

Isomerism refers to compounds with the same molecular formula but different structures, impacting properties. Learn about the different types of isomerism with examples in this quick guide.

By Topperlearning Expert 19th Apr, 2024 | 06:00 pm

The compounds are said to be isomers if they exist in two or more forms without varying the molecular formula. The change in configuration or structure of the compound leads to modified properties. The phenomenon is called Isomerism.

It broadly has two types, followed by subcategories:

Structural isomerism: This is due to different structures, which result in the chain, position, functional group, and meta isomerism.
Stereoisomerism: It arises due to differences in the relative position of atoms or groups. It can be geometric or optical isomerism.

Types of Structural Isomerism with Examples

The following sections will help you understand the different types of isomers with examples:

Chain Isomers:

They differ in the arrangement of carbon atoms. Butane has a straight chain, while iso-butane has a branched structure.

Example: Butane and iso-butane (2-methylpropane)

Functional group Isomers:

They share the same molecular formula but differ in the arrangement of functional groups. There is an aldehyde in butanal and ketone in butanone.

Example: Butanal and Butanone

Positional Isomers:

They have the same molecular formula but differ in the position of the hydroxyl (OH) group. It is located at the first and second carbon, respectively.

Example: Butan-1-ol and Butan-2-ol

Metamerism Isomers:

They share the same functional group and molecular formula. However, they differ in the arrangement of the alkyl groups on either side of the functional group.

Example: 3-Pentanone and 2-Pentanone

Types of Stereoisomerism with Examples

The following sections will help you understand the different types of isomers with examples.

Geometrical Isomers:

They have the same molecular formula but differ in the spatial arrangement of atoms around the double bond. Here, cis has similar groups on the same side, while trans has them on opposite sides.

Example: cis-2-butene and trans-2-butene

The cis and trans isomeric system poses difficulty when dealing with alkenes with two functional groups attached to each side of carbon. The E/Z nomenclature for geometric isomerism comes into play in the situation. Here, consider the left and right sides of the carbon and check the priority of the groups determined by the atomic number or other deciding rules. If the two highest-priority substituents are on the same side of the double bond, it is a Z-isomer. If the two highest-priority substituents are on opposite sides, it is named an E-isomer.

Example: (Z)-2-bromo-3-chloro-2-butene and (E)-2-bromo-3-chloro-2-butene

Optical Isomers:

Chirality:

Chirality refers to a molecule’s potential to exist as two asymmetric forms. It describes the spatial arrangement of atoms or groups in a molecule. Chiral Centre: An atom with four different groups bonded to it is considered as the chiral center. Enantiomers: The molecules are said to be enantiomers if they are the non-superimposable mirror image forms. The enantiomers are recognized at a chiral center.

Example: R and S isomers of Butan-2,3-diol

Diastereomers:

The molecules are said to be diastereoisomers if they are non-superimposable and non-mirror images of each other.

Example: Enantiomers and diastereoisomers of D-galactose.

Conclusion

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FAQ's

Q 1. How do you name isomers in IUPAC?

Ans: There are three steps to the naming of isomers:

The branch group is indicated by the prefix. It is the alkyl group attached to the longest carbon chain.
The root name depicts the number of carbon atoms in the longest carbon chain.
The suffix indicates the homologous series.

Q 2. What is the formula for the number of isomers for a compound?

Ans: The formula for the number of isomers of a compound is 2n, where ‘n’ is the number of chiral carbons in the compound.

Q 3. How can isomerism impact the properties of compounds?

Ans: Isomerism can lead to different physical and chemical properties, like boiling points, melting points, and reactivity. This difference occurs due to variations in structural arrangements.