Hydrocarbons - Isomerism in Alkanes

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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 C₄H_10. 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