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Butane is an alkane hydrocarbon with the empirical formula C4H10.

It is a flammable, colorless, easily liquefied gas that is used extensively as a fuel for cigarette lighters and portable stoves.

Butane exists as two isomers:

n-butane is a fully hydrogenated linear chain of four carbon atoms: CH3CH2CH2CH3. Its boiling point is -0.6 °C and its melting point is -138.3 °C.

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.