Coal and Petroleum


   
 
Hydrocarbons - Isomerism in Alkanes
Isomers are compounds having the same molecular formula but different properties due to different structural arrangement of atoms in their molecules.
 
Isomers with the same formula have the following characteristics:
 
Same molecular formula
 
Different structural formula
 
Different physical properties (e.g., boiling point)
 
Similar or different chemical properties
 
Same molecular mass
 
The minimum number of carbon atoms required to form isomers is four. Butane is the first alkane that can exhibit isomerism. The first three alkanes cannot exhibit isomerism because there can be no change in their three dimensional structure of the molecules.
 
Isomerism in butane
 
The molecular formula of butane is C4H10. With this molecular formula, there are two structural arrangements possible as shown below:
 
 
 
Isomerism in Pentane
 
The molecular formula of pentane is C5H12. With this formula, three isomers are possible.
 
1.
 
 
2.
 
 
3.
 
 
Isomers of hexane
 
The molecular formula of hexane is C6H14. With this molecular formula five isomers are possible. Their structures and IUPAC names are as follows:
 
1.
 
 
               n-hexane
            (hexane)
 
2.
 
 
          Iso-hexane
    (2-methylpentane)
 
3.
 
 
    3- methyl 1-pentane
 
4.
 
 
    2,3 - dimethylbutane
 
5.
 
 
    2,2 - dimethylbutane
 
  
     
   
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