The isomers which arise due to the different arrangement of atoms within the molecule are known as the structural isomers. These are also known as constitutional isomers. For example, butanol, methyl propyl ether, and diethyl ether have similar chemical formulas but different arrangements of atoms. There are mainly three types of structural isomers.

Types of structural isomers

There are the following types of structural isomers:

Chain isomers

“The type of isomers which has the same molecular formula but different arrangements of the carbon chain is known as chain isomers.”

These isomers are also known as nuclear isomerism and skeletal isomerism.

For example, pentane has three chain isomers.

  • n-pentane
  • isopentane
  • neopentane

Position isomers

“The isomers arise due to the different positions of functional groups in a carbon chain and are known as position isomers. “

For example, chloropropane has two position isomers.

  • 1-Chloropropane
  • 2-Chloropropane

Butene has two position isomers.

  • 1-Butene
  • 2-Butene

Functional group isomers

“The type of isomerism with the same molecular formula but a different functional group is known as functional group isomerism.”

For example, the two compounds have similar molecular formula C2H6O but different functional groups.

Another example of functional isomerism is shown by the compounds having similar molecular formula C3H6O2.


“In this type of structural isomers, the two compounds have the same molecular formula but different distribution of carbon atoms on either side of the functional group.”

For example, 2-pentanone and 3-pentanone are metamers to each other.

Ethoxyethane and 1-methoxypropane are also metamers of each other.


“The type of structural isomers that arises due to the shifting of the proton from one atom to another in the same molecule is known as tautomers.”


  • Keto-enol tautomerism

  • Zwitterion formation

Structural isomers of alkanes

There are the following structural isomers of alkanes.

Isomers of methane

The simplest alkane is methane which consists of single carbon. This carbon is covalently bonded to the four hydrogen atoms. The condensed formula of methane is CH4.

It is believed that there are no structural isomers for methane. But the carbon-hydrogen bond in methane vibrates and bends so we can say that isomerism can exist but for a short time period.

Isomers of ethane and propane

The condensed formula of ethane and propane is C2H6 and C3H8 respectively. The ethane and propane do not show structural isomerism. This is because there is only one way to arrange the carbon atoms.

Isomers of butane

Butane is an alkane with four carbon atoms. The molecular formula of butane is C4H10. There are two structural isomers that are possible for the butane. These isomers are n-butane and iso-butane.

These two structural isomers have different chemical and physical properties.

Isomers of pentane

The alkane with five carbon atoms is pentane. Its molecular formula is C5H12. There are three structural isomers that are possible for the pentane. These isomers are n-pentane, iso-pentane (methyl butane), and neo-pentane( dimethylpropane).

Isomers of hexane

Hexane consists of six carbon atoms. Its molecular is C6H12. There are five structural isomers of hexane, for example, n-hexane, 2-methyl pentane, 3-methyl pentane, 2,3-dimethyl butane, and 2,2 dimethylbutane.

Isomers of heptane

The molecular formula of heptane is C7H16. There are nine different structural isomers of heptane. These isomers show different physical and chemical properties.

The isomers of heptanes are the following:

  • n-heptane
  • 2-Methyl hexane
  • 3-Methylhexane
  • 2,3-Dimethylpentane
  • 2,2-Dimethylpentane
  • 2,4-Dimethylpentane
  • 3,3-Dimethylpentane
  • 3-Ethylpentane
  • 2,2,3-Trimethylbutane

Key Takeaways

Concepts Berg

What is structural isomerism?

The type of isomerism in which compounds have the same molecular formula but are arranged in a completely different order is known as structural isomerism.

What are C4H9Br isomers?

There are four structural isomers possible for the C4H9Br. They are as follows:

  • Bromobutane
  • 2-Bromobutane
  • 2-Bromo-2-methylpropane
  • tert-Butyl bromide

How many structural isomers are possible for C2H4Br2?

There are two structural isomers possible for the C2H4Br2. These are the following:

  • 1,1-Dibromoethane
  • 1,2-Dibromoethane

How do structural isomers and stereoisomers differ?

Structural isomers have the same molecular formula but different atomic arrangements. Whereas the stereoisomers have the similar molecular formulas and atomic arrangements. They have different spatial arrangements

What are the structural isomers of glucose?

Galactose and fructose are the structural isomers of glucose.


What is the difference between structural and constitutional isomers?

Structural and constitutional isomers are the same. There is no difference between them.

Reference Books

  • Learn Isomerism in Pictorial way by Ajnish Kumar Gupta

Reference Links