Isomers of butane. Molecular model of two isomers of butane (C4.H10). Isomers are chemicals with the same atoms, but different molecular arrangements. Butane has carbon atoms (black) and hydrogen atoms (white) and no double bonds, making it a saturated hydrocarbon (or alkane). These two isomers differ in their structure, being structural isomers. The naming of alkanes uses the longest chain of carbon atoms. On the left is n-butane, while on the right is iso-butane (2-methylpropane). Both isomers are colourless gases found in natural gas. Iso-butane boils at a lower temperature than n-butane because the branched side-chain makes it more compact.