How many structural isomers can you draw for pentane?



Compounds that have the same chemical formula but different structures are known as structural isomers.


  • It means that they have the same number of each atom, but the placement of the atoms is different.

Pentane means 5 (pent) carbon atoms all having single bonds(-ane). 


The simplest 5 carbon compound we can draw is by placing all five in a straight line. 

  • So first, we will place 5 carbon atoms in a straight line , and place the H atoms in a way that satisfies their valency. This structure is known as n-pentane.

N-PENTANE - Teachoo.jpg

STEP 2  

Next, we can try to make a branching structure.

  • We take one of the carbon atoms on the end, and place it on the middle carbon forming a side branch. 
  • Then, we place the hydrogen atoms in a way that satisfies the valency of the C- atoms.
  • This structure is also known as Isoprene .

ISO-PENTANE - Teachoo.jpg

Now, we repeat step 2 till we can no longer form distinct structures.

  • Again, we take a carbon from the end, and try to form a different structure
  • If we take the C-atom on the left and place it in another branching structure on the central atom, we get a compound called neo-pentane. 
  • H-atoms are placed in a way that satisfies the Carbon atom’s valencies. 

NEO-PENTANE - Teachoo.jpg

  • If we try to place more C-atoms from one end to the branches, we form the same compounds that we saw before. 
  • Hence, Pentane can have a total of  3 structural isomers, (i.e.) namely, n-pentane, isopentane and neopentane.

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CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo