What is isomerism?
Isomerism is a phenomenon in which two or more molecules have the same chemical formula, but different arrangements of atoms within their structures, resulting in distinct chemical and physical properties. Isomers are molecules that have the same number and types of atoms, but different spatial arrangements of these atoms.
Types of isomerism:
Isomerism is the phenomenon in which molecules or compounds have the same molecular formula but differ in their arrangement or connectivity of atoms. There are several types of isomerism, including:
1- Structural Isomerism:
Also known as constitutional isomerism, this type of isomerism occurs when compounds have the same molecular formula but differ in their connectivity of atoms. This type of isomerism can be further divided into:
a) Chain Isomerism:
- Molecules that have the same molecular formula but different arrangements of the carbon chain.
b) Position Isomerism: - Molecules that have the same molecular formula but different positions of a functional group.
c) Functional Group Isomerism: - Molecules that have the same molecular formula but different functional groups.
- This type of isomerism occurs when compounds have the same molecular formula and connectivity of atoms, but differ in their three-dimensional arrangement of atoms in space. Stereoisomerism can be further divided into:
a) Geometric Isomerism:
- Molecules that have the same molecular formula and connectivity of atoms but differ in their spatial arrangement due to the presence of a double bond or a ring structure.
- For example, consider the compound 2-butene, which has a double bond between the second and third carbon atoms. Depending on the orientation of the substituent groups attached to the double bond, 2-butene can exist in two geometric isomeric forms: cis-2-butene and trans-2-butene.
b) Optical Isomerism: - Molecules that have a non-superimposable mirror image and can rotate the plane of polarized light differently.
- For example, consider the compound 2-chlorobutane, which has an asymmetric carbon atom.
3- Tautomerism:
For example, acetaldehyde can exist in two tautomeric forms: the keto form and the enol form, as shown below:
In the keto form, acetaldehyde has a carbonyl group attached to a carbon atom, and in the enol form, it has a hydroxyl group attached to the adjacent carbon atom. These two forms are in equilibrium with each other and can interconvert by the movement of a proton. The enol form is less stable than the keto form, and the equilibrium between the two forms is shifted towards the keto form.
4- Metamerism:
This type of isomerism occurs when compounds have the same molecular formula and connectivity of atoms, but differ in the alkyl groups attached to the functional group.
One common example of metamerism is the isomers of butyl alcohol, which have the same molecular formula C4H10O but differ in the identity and arrangement of the alkyl group attached to the hydroxyl functional group.
The three isomers of butyl alcohol are n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol, as shown below:
5- Polymerism:
This type of isomerism occurs when compounds have the same molecular formula, but one is a monomer (a small molecule) and the other is a polymer (a large molecule made up of repeating monomer units).
Applications of isomerism:
Isomerism has many practical applications in various fields of science and industry. Some of the important applications of isomerism are:
Drug Development:
Isomerism plays a crucial role in the development of new drugs. Stereoisomers of drugs can have different pharmacological properties and can interact differently with the body’s enzymes and receptors. For example, the drug thalidomide has two stereoisomers, one of which caused birth defects, while the other was a highly effective sedative.
Food Industry:
Isomerism is used in the food industry to create different flavors and aromas. For example, the compound limonene has two stereoisomers, which have different smells – one smells like oranges and the other like lemons.
Materials Science:
Isomerism is used to create materials with different properties. For example, polypropylene can exist in two different stereoisomeric forms, which have different melting points and mechanical properties. These different forms can be used to create different types of plastic products.
Chemical Analysis:
Isomerism is used in chemical analysis to separate and identify different compounds. For example, gas chromatography can be used to separate different stereoisomers of a compound, allowing scientists to study their properties and interactions.
Organic Synthesis:
Isomerism is used in organic synthesis to create different compounds with specific properties. For example, the synthesis of steroids and other hormones often involves the creation of specific stereoisomers to produce desired biological effects.
Overall, the study and understanding of isomerism have practical applications in various fields, including medicine, food science, materials science, chemical analysis, and organic synthesis.