Structural Isomerism
Structural Isomerism is the phenomenon of organic compound having same molecular formula but different structural arrangements. The compounds which shows the property of structural isomerism are called Structural Isomers. There are in total six types of structural isomerism.
In this article, we will learn in detail about structural isomers, structural isomerism, its types and examples in detail. Before getting into Structural Isomerism, let’s understand first What is an Isomer?
Isomer and Isomerism
An isomer is a molecule that has a identical molecular formula means the number of atoms of each type should be the same but differs in the arrangement of atoms in space.
While,
Isomerism is the phenomenon in which more than one compounds have the same chemical formula but have a difference in their chemical structures.
Example: n-Butane and isobutane are isomers of Butane. They have same molecular formula C4H10 while if see the arrangement, then in n-butane, there is a straight chain of 4 carbon atoms while in isobutane there is a straight chain of three carbon and the fourth carbon is linked to the middle carbon as a branch.
Structural Isomers Definition
Those isomers in which the atoms are completely arranged in a different order and bonding but the same molecular formulas. More simply, Compounds having the same molecular formula but different structures are known as Structural Isomers.
Structural isomers are also called as constitutional isomerism.
Example: butane and Isobutane
Structural Isomerism Definition
The isomers differing in the atomic arrangement of the molecules with the same molecular formula are known as structural isomers. The phenomenon of these structural isomers is called structural isomerism.
Structural isomerism is also called Constitutional Isomerism.
Types of Structural Isomerism
The six different types of structural isomers are mentioned below:
- Chain Isomerism
- Positional Isomerism
- Functional Isomerism
- Metamerism
- Tautomerism
- Ring-Chain Isomerism
Let’s learn them one by one in detail along with their examples are discussed below:
Chain Isomerism
The type of structural isomerism in which the two or more compounds have the same type of molecular formula with having difference in the main chains is called as Chain Isomerism. The two forms of chain isomerism are linear and branched isomerism.
Chain isomerism is also called as Skeletal Isomerism.
Example: C5H12: Pentane, Neo-Pentane, and Iso-Pentane. The structural image is shown below:
Positional Isomerism
The type of structural isomerism in which the position of the functional group is different with respect to the main chain is called as Positional Isomerism.
Example: C3H8O: 1-propyl alcohol, and 2-propanol. The structural image is shown below:
Functional Isomerism
The type of structural isomerism in which the compound have different functional groups of same number of atoms is called as Functional Isomerism. This is also called as Functional Group Isomerism.
Example: C3H6O: Propanone and Propanal
Metamerism
The type of structural isomerism in which different alkyl groups on either side of functional groups are present is called as Metamerism.
Example: C4H10O: Diethyl Ether and Methyl Propyl Ether
Tautomerism
The type of structural isomerism in which two isomers are in a stable dynamic equilibrium is called as Tautomerism. This is a special type of functional isomerism.
Example: C3H6O: Ketone and Enol
Ring-Chain Isomerism
The type of structural isomerism in which different chain structures appear to be connected in a ring pattern is called as Ring-Chain Isomerism.
They have two different structures as cyclic, and as open-chain.
Example: C3H6: Propene and Cyclopropene
Structural Isomers of Organic Compounds
The structural isomers of some common organic compounds are mentioned below:
Structural Isomers of Butane
Butane has a molecular formula of C4H10. There are two possible isomers of butane mentioned below:
- n-Butane, also called as unbranched butane (IUPAC: butane)
- Iso butane, also called as i-butane (IUPAC: 2-methylpropane)
Structural Isomers of Pentane
Pentane has a molecular formula of C5H12. There are three possible structural isomers of pentane mentioned below:
- n-Pentane, also called as unbranched pentane (IUPAC: pentane)
- Iso pentane (IUPAC: 2-methyl butane)
- Neo pentane (IUPAC: 2,2-dimethylpropane)
Structural Isomers of Hexane
Hexane has a molecular formula of C6H14. There are 5 isomers of hexane. Following are their IUPAC name:
- n-hexane
- 2-methyl pentane
- 3-methyl pentane
- 2,2-dimethyl butane
- 2,3-dimethyl butane
Structural Isomers of Heptane
Heptane has a molecular formula of C7H16. There are 9 isomers of heptane. Following are their IUPAC name:
- n-heptane
- 2-Methylhexane
- 3-Methylhexane
- 2,2-Dimethylpentane
- 2,3-Dimethylpentane
- 2,4-Dimethylpentane
- 3,3-Dimethylpentane
- 3-Ethylpentane
- 2,2,3-Trimethylbutane
Stereoisomers vs Structural isomers
Stereoisomer and Structural Isomers are two different kinds of isomerism possible in organic compounds. Here is the key differences between the stereoisomers and structural isomers:
Structural Isomer |
Stereoisomer |
---|---|
The arrangement of the atoms in different molecules is different |
Spatial arrangement of the atoms are different. |
They are of 6 types, namely Chain, Positional, Functional, Metamers, Tautomers, and Ring- chain. |
They are of two types, namely Optical, and Geometrical isomers. |
They have different connectivity. |
They have different spatial arrangements. |
FAQs on Structural Isomerism
What are structural isomers?
Compounds having the same molecular formula but different structures are known as Structural Isomers.
What is structural isomerism?
The phenomenon of these structural isomers is called structural isomerism. It is also called as constitutional isomerism.
What are types of structural isomers?
They are of 6 types, namely Chain isomers, Positional isomers, Functional isomers, Metamers, Tautomers, and Ring- chain isomers.
How many structural isomers can you draw for pentane?
We can draw 3 structural isomers of pentane, namely n-pentane, Iso-pentane (methyl butane), and neopentane (dimethylpropane).
Are structural isomers possible for bromopentane?
Yes, structural isomers for bromopentane are possible. They are bromopentane, and 2-bromopentane.