The Butane reference article from the English Wikipedia on 24-Apr-2004
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Butane

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Butane is an alkane hydrocarbon with the empirical formula C4H10. It has the following display formula:

    H   H   H   H

    |   |   |   |

H - C - C - C - C - H

    |   |   |   |

    H   H   H   H
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 -11.7 °C and its melting point is -159.6 °C.

Image:N&i-butane.png

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.