Organic Chemistry


Isn’t it funny that with the same chemical formula, two compounds can exhibit different properties? Are they twins or something? Well, no! This is about a concept known as isomerism. Let us study this concept in greater detail. We will look at its types and examples as well.

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What is Isomerism?

It is a phenomenon where two or more compounds have the same chemical formula but possesses different structural formulas and different properties. This is mainly because of different structural or spatial arrangements. Isomers are the compounds exhibiting this phenomenon.

Types of Isomerism

Basically, there are two types. They are:

  • Structural Isomerism
  • Stereoisomerism

However, these are again of many subtypes as shown in the figure:


Structural Isomerism

Isomers are structural isomers when they have the same molecular formula but different structures. Structural isomerism is further of the following types. Let’s learn about these types, one-by-one.

Learn the different Characteristics of Organic Compounds here.

1) Chain Isomerism

Isomers are chain isomers when two or more compounds have the same molecular formula but differ in the branching of carbon atoms. For example, we can represent C5H12 as three compounds: CH3CH2CH2CH2CH3– pentane


2) Position Isomerism

Isomers are position isomers when the two or more compounds differ in the position of the functional group or substituent atoms. For example, we can represent C3H7OH in two arrangements:

CH3CH2CH2OH                    -Propan-1-ol


3) Functional Isomerism

Isomers are functional isomers when the two or more compounds have an identical molecular formula but differ in the functional group present. For example, we can represent C3H6O as a ketone and as an aldehyde.


4) Metamerism

This is exhibited by compounds due to the presence of different alkyl chains on either side of the functional group. For example, we can represent C4H10O as ethoxyethane (C2H5OC2H5) and methoxypropane (CH3OC3H7)

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Stereo Isomerism

Stereoisomerism is a phenomenon in which compounds have the same molecular formula but differ in the relative positioning or orientation of atoms in space. Stereoisomers are the compounds exhibiting stereoisomerism. We can further classify stereoisomerism into:

  • Geometric Isomerism: it is shown by molecules in which their spatial positions are locked to each other due to the presence of a ring structure or a double bond.
  • Optical Isomerism: Two or more compounds that have the same molecular arrangement but differ in the optical activity are optical isomers.

Learn more about different types of Organic Reaction here.

Solved Examples for You

Q1: What is a chiral carbon?

Ans: If all the four valencies of carbon are satisfied by four different atoms or four different groups of atoms, then carbon is known as chiral carbon.

Q2: What is tautomerism?

Ans: It is the type of isomerism in which two functional isomers exist together in equilibrium. The two forms existing in equilibrium are called as tautomers.

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