Alkene

In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond.^[1] The double bond may be internal or in 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.^[2][3][4]

Acyclic alkenes, with only one double bond and no other functional groups (also known as mono-enes) form a homologous series of hydrocarbons with the general formula C_nH_2n with n being a >1 natural number (which is two hydrogens less than the corresponding alkane). When n is four or more, isomers are possible, distinguished 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. The simplest alkene, ethylene (C₂H₄) (or "ethene" in the IUPAC nomenclature) is the organic compound produced on the largest scale industrially.^[5]

Aromatic compounds are often drawn as cyclic alkenes, however their structure and properties are sufficiently distinct that they are not classified as alkenes or olefins.^[3] Hydrocarbons with two overlapping double bonds (C=C=C) are called allenes—the simplest such compound is itself called allene—and those with three or more overlapping bonds (C=C=C=C, C=C=C=C=C, etc.) are called cumulenes.