Atoms in a given molecule may be arranged differently giving rise to structural isomers. There are three types of structural isomers which are chain, positional and functional group isomers.
Isomers
Molecules with the same molecular formula as one another but with a different arrangement of atoms are known as isomers. There are two types of isomers:
Structural isomers
Stereoisomers
Stereoisomers are molecules with the same molecular and structural formula but with a different arrangement of atoms in space.
Structural isomers
There are three types of structural isomers:
Chain isomers
Positional isomers
Functional group isomers
Chain isomers
The carbon skeleton of each molecule differs from one another. One molecule may have a straight chain whilst the other is branched. These isomers have the same chemical properties but have different physical properties.
Example
Molecular formula: C4H10
A. Butane; B. 2-methylpropane
Positional isomers
In positional isomers the isomers have the same functional group however they are positioned in a different part of the carbon chain. These isomers have different physical properties and may have different chemical properties.
Example
Molecular formula: C3H8O
A. Propan-1-ol; B. Propan-2-ol
Functional group isomers
In this type, the same atoms are arranged into different functional groups. These isomers have different chemical and physical properties.
Example
Molecular formula: C2H6O
A. Dimethyl ether; B. Ethanol
Important: There is a degree of flexibility around C−C bonds. This means a molecule may seem to have an isomer but in fact it is the same molecule rotated differently.