Butane exists as two isomers:
i-butane, or isobutane, has the formula CH3CH(CH3)2, and the systematic name 2-methylpropane. Its boiling point is -0.5 °C and its melting point is -159.6 °C.
Recent concerns with depletion of the ozone layer by freon gases have led to increased use of isobutane as a gas for refrigeration systems, especially in domestic refrigerators and freezers. When used as a refrigerant, isobutane is also known as R600a.