Alkanes:

Alkanes of a specific molecular formula can present as different constitutional isomers. For instance, the alkane that comprising the molecular formula C₄H₁₀ can available as two constitutional isomers that is:

1. The straight chain alkane (butane) or

2. The branched alkane (2-methylpropane).

These are dissimilar compounds with diverse physical and chemical properties.

Figure:   (a) Butane (C₄H₁₀); (b) 2-methylpropane (C₄H₁₀).