Butane is the n = 4 case in the series of alkane single-bond chain hydrocarbons, each made up of n carbon atoms and 2n+2 hydrogen atoms. The two forms of butane are n-butane and 2-methyl-propane. An unofficial name for the second form of butane is isobutane, because it is the one and only isomer of the chemical.

n-butane boils at -0.5° C (31.1° F); isobutane boils at -11.7° C (10.9° F).