Alkene

In organic chemistry, an alkene, or olefin, is a hydrocarbon containing one or more carbon–carbon double bonds. The double bond may be internal or at the terminal position. Terminal alkenes are also known as α-olefins. The International Union of Pure and Applied Chemistry (IUPAC) recommends using the name "alkene" only for acyclic hydrocarbons with just one double bond; alkadiene, alkatriene, etc., or polyene for acyclic hydrocarbons with two or more double bonds; cycloalkene, cycloalkadiene, etc. for cyclic ones; and "olefin" for the general class – cyclic or acyclic, with one or more double bonds. Acyclic alkenes having only one double bond (known as mono-enes) form a homologous series of hydrocarbons with the general formula CnH2n, where n is at least two, which is two fewer hydrogens than the corresponding alkane (CnH2n+2). When n is four or more, as in butene, there are isomers that are distinguished by the connectivity of the carbon skeleton and by the position and conformation of the double bond. Alkenes are generally colorless non-polar compounds, somewhat similar to alkanes but more reactive. The first few members of the series are gases or liquids at room temperature. They are produced industrially by steam cracking and dehydrogenation of hydrocarbons from natural-gas condensate and petroleum. They are used to produce polymers such as polyethylene and as precursors to many industrial chemicals. The simplest alkene, ethylene (C2H4) (or "ethene" in the IUPAC nomenclature) is the organic compound produced on the largest scale industrially. Aromatic compounds are often drawn as cyclic alkenes, but their structure and properties are sufficiently distinct that they are not classified as alkenes or olefins. Hydrocarbons with two successive double bonds (C=C=C) are called allenes—the simplest such compound is itself called allene—and those with three or more successive double bonds (C=C=C=C, C=C=C=C=C, etc.) are called cumulenes.