Structural Isomerism

Structural Isomerism

Isomers and Structural Isomers:

Isomers: Isomers are the molecules having similar kind of molecular formula with a different arrangement of atomic spacing in space. These various forms of arrangements are due to the rotation of the molecule as a whole or due to the rotating about its particular bonds.

Consider the example, in the image below of butane, both are the similar type of molecules, but these are not isomers.


There are a number of ways that this molecule can twist by itself. There is a complete free rotation around the single bonds of carbon to carbon atoms.

Structural Isomers:These are the isomers in which the atoms are completely arranged in different order with same molecular formulas.

These are the molecules having the same kind of molecular formula with different connectivities depending upon the order they are put together. The structure of Alkane(C4H10) is one of the simple examples representing a structural isomer with different isomers. With the increase in the number of Carbon atoms in the alkane molecule, the structural isomers increase.

Structural Isomerism:

The isomers differing in the atomic arrangement of the molecules without any kind of reference to the spatial arrangement are known as the structural isomers. The phenomenon of this structural isomers is called as structural isomerism.

The Structural isomerism is also called as constitutional isomerism as per the IUPAC. It is kind of isomerism where the molecules having the same molecular formula with different orders and bondings, as opposed to that of the stereoisomerism.

Types of Structural Isomerism:

There are three types of Structural isomerism existing namely chain isomerism, position isomerism and functional group isomerism.

  • Chain Isomerism:Chain isomerism occurs when a there is a difference in the atomic arrangement of the carbon to the carbon chain of a molecule. If two or more compounds having the same type of molecular formula with different main chains, then they are said to exhibit the property of Chain isomerism. This phenomenon is also called as skeletal isomerism.
  • Position Isomerism:Positional isomerism arises when there is a difference in the positions occupied by the substituent atoms or a group of atoms or due to the unsaturation occurring in the chain. When the position of the functional groups with respect to main chain atom changes, the phenomenon is called as position isomerism.
  • Functional Group Isomerism:The Functional group isomerism occurs when there is a  presence of the odd form of functional groups with the same chemical formula. When some compound has two different structures but same chemical formula, then it is said to exhibit functional isomerism.