butane (byōō´tān), C4H10, gaseous alkane, a hydrocarbon that is obtained from natural gas or by refining petroleum. It can be liquefied at room temperature by compression. There are two structural isomers of butane. In normal butane, or n-butane, the four carbon atoms are joined in a continuous, unbranched chain; in isobutane, or 2-methylpropane, three of the carbon atoms are joined to the fourth by single bonds, resulting in a branched structure. The two isomers differ in certain of their chemical and physical properties, e.g., liquid n-butane has a higher boiling point (-0.6°C) at atmospheric pressure than that of liquid isobutane (-10.2°C).