Isobutane

Part of speech: noun

Definitions

1. A branched-chain hydrocarbon with four carbon atoms that is classified as an alkane
2. A colorless and flammable gas at ambient conditions, often used as a refrigerant and fuel source
3. A saturated hydrocarbon consisting of four carbon atoms arranged in a branched structure, utilized in refrigeration and as a fuel source

Etymology: Isobutane is a plain technical coinage, built from the prefix "iso-" and the word "butane." The prefix comes from the Greek "isos," meaning "equal" or "same," and in chemistry it marks a compound whose atoms are arranged differently from another compound with the same molecular formula. Isobutane and butane share the formula C4H10, but in isobutane the carbon atoms form a branched chain rather than a straight one. The name therefore records a relationship rather than a substance. Chemists needed a way to distinguish the branched form from the straight-chain one, which is why "n-butane," short for "normal butane," was the standard label for the unbranched version. "Isobutane" is simply the name given to the branched arrangement, and it is the sort of coinage that appeared as chemists systematically named the isomers of hydrocarbons.