# What are the isomers of butane?

Butane, or ${C}_{4} {H}_{10}$, has two structural (also called constitutional) isomers called normal butane, or unbranched butane, and isobutane, or i-butane. According to IUPAC nomenclature, these isomers are called simply butane and 2-methylpropane.
Notice that isobutane has a propane parent chain with a methyl group - $C {H}_{3}$ attached to the second carbon of the chain - that is why its IUPAC name is 2-methylpropane.