What is meant by isomers ? Draw the structure of two isomers of butane, `C_(4)H_(10)`. Explain why we cannot have isomers of first three members of alkane series.

Explanation

Isomers are the compounds which have the same molecular formula but different structural formula.
Isomers of Butane:
`H-underset("n-butane")(underset(H)underset(|)overset(H)overset(|)(C)-underset(H)underset(|)overset(H)overset(|)(C)-underset(H)underset(|)overset(H)overset(|)(C)-underset(H)underset(|)overset(H)overset(|)(C)H)`
(ii) `H-underset(|)overset(H)overset(|)(C)-H`
`H--underset(H)underset(|)overset(H)overset(|)(C)--underset(H)underset(|)overset(H)overset(|)(C)--underset(H)underset(|)overset(H)overset(|)(C)H`
We cannot have isomers of the first three members of the alkane series because of the following laws of isomers :
(i) The parent chain should have the most number of carbon atoms.
(ii) The branching cannot be done from the first on the last atom carbon atom of the structure.