XII Chemistry BIEK Topic - Isomerism (Short Note)

Isomerism (Short Note)
Definition
The phenomenon in which different compounds have the same molecular formula but different structural formula or electronic configuration is known as Isomerism.

The different compounds are called Isomers.




Types of Isomerism
There are various types of isomerism, but the four important types are

1. Chain Isomerism

2. Position Isomerism

3. Functional group Isomerism

4. Metamerism


1 Chain Isomerism

The phenomenon in which different compounds have the same molecular formula but differ in length of carbon chain is called Chain Isomerism. The structures are known as Chain Isomers.


Examples

1. Methane, Ethane and Propane have no chain isomers because the cannot be rearranged with small carbon chain.

CH4 CH3-CH3 CH3-CH2-CH3


2. The carbon chain of butane (C4H10) is long enough. So, butane has two isomers.

CH3-CH2-CH2-CH3 (n-butane)

CH3-CHCH3-CH3 (iso-butane)


3. Pentane (C5H12) shows the following isomers.

CH3-CH2-CH2-CH2-CH3 (N-PENTANE)

CH3-CHCH3-CH2-CH3 (ISO-PENTANE)

In saturated hydrocarbons, the number of isomers increase with increase in number of carbon atoms. This is the reason why decane shows 75 isomers.

2. Position Isomerism

The phenomenon in which different compounds have same molecular formula but differ in position of functional group, double bond or triple bond in same length of carbon chain is called Position Isomerism. The structures are called Position Isomers.


Examples

1. Propyl alcohol shows two position isomers.

Diagram Coming Soon

2. Butene C4H8 has two position isomers.

Diagram Coming Soon

3. Functional Group Isomerism

The phenomenon in which different compounds have same molecular formula but differ in functional groups is called functional group Isomerism. The structures are known as functional group isomers.


4. Metamerism

The phenomenon in which different compounds have same molecular formula and functional group but different alkyl groups attached to the same multivalent atom is called metamerism.