What are isomers?

What are Isomers?

When two or more compounds having the same formula but different structures are called isomers.

Example 1

n-butane and Isobutane both have the same chemical  formula C 4 H 10 .But they have different structure . .

Explanation for n-butane

• n-butane means Normal Butane
• Formula for normal butane is C ₄ H ₁₀
• ‘but’ stands for 4, hence it has 4 carbon atoms
• Number of hydrogen atoms = 2 × Carbon Atoms + 2 = 2 × 4 + 2 = 8 + 2 = 10

Hence we get formula C ₄ H ₁₀

In n butane, we show all 4 carbon atoms together as shown below

Example 2

n-pentane, Isopentane and neopentane all have formula C5H12, but different structures.

Explanation for n-pentane

• n-Pentane means Normal pentane
• Formula for Normal pentane is C ₅ H ₁₂
• ‘pent’ stands for 5, hence it has 5 Carbon atoms
• Number of Hydrogen Atoms = 2 × Carbon Atoms + 2 = 2 × 5 + 2 = 10 + 2 = 12
• Hence we get formula C ₅ H ₁₂

In n pentane, we show all 5 carbon atoms together as shown below:

Explanation for isopentane: 

• The formula for isopentane is also C ₅ H ₁₂ however the arrangement is different . 
• In this 4 carbon atoms are in a chain and 1 carbon atom forms a branch at the 2nd carbon of the chain. The structure of isopentane is as follows:

Explanation for neopentane:

• The formula for neopentane is also C ₅ H ₁₂ , but the arrangement is different. 
• In this 3 carbon atoms form the chain and the remaining 2 form branches on the second carbon atom of the chain as shown in the figure below: