Question

# What is isomerism? Write the isomers of butane?

Hint: Try to break the word isomerism into two parts to get an idea about the meaning of the word. Now if you have cracked the meaning try making isomers of butane and remember it is an alkane.

Isomerism - Isomers are molecules with the same molecular formula but different structural formulas. This phenomenon is called isomerism.
Due to different structures, isomers may have different chemical and physical properties also.
Isomers of butane -
Constitutional Isomers of Butane -
There are four carbon atoms in the butane’s molecular formula ${ C }_{ 3 }{ H }_{ 8 }$. So these four carbon atoms can arrange in two different manners.
They can either arrange in the straight chain of four carbon atoms or they can form a chain of 3 carbon atoms with one side chain.

Here, straight chain is called n-butane and branched chain is called isobutane(or 2-methylpropane). Notice that isobutane has a propane parent chain with a methyl group attached to the second carbon of the chain, that is why its IUPAC name is 2-methylpropane.
Conformational Isomers of Butane -
Stereoisomers which can be converted into one another by rotation around a single bond are called conformational isomers.
Alkanes usually show conformational isomerism because of the presence of C-C bonds.
For example, when we rotate the molecule of butane at the axis of C-C bond, we get eclipsed, gauche, and anti butane conformational isomers.
Here, eclipsed conformation has identical groups directly in-line with one another that makes it unstable.
Gauche conformation stands for the presence of identical groups at 60 degrees from one another. It is more stable compared to eclipse confirmation due to less steric hindrance between the same molecules.
In anti conformation, identical groups are 180 degrees from one another which makes it the most stable form.

Therefore, we defined what is isomerism and explained the isomers of butane.

Note: In butane Each conformer is interconverted by rotating around the central carbon single bond like an eclipsed conformer can convert into gauche conform by rotating 60 degrees. Rotation of eclipsed by 180-degree forms anti- conformer. Rotation of anti butane by 120 degrees forms gauche conformer.