Carbon–carbon double bond
In organic chemistry, an alkene is an unsaturated hydrocarbon that contains at least one carbon–carbon double bond. The words alkene and olefin are often used interchangeably (see nomenclature section below). Acyclic alkenes, with only one double bond and no other functional groups, known as mono-enes, form a homologous series of hydrocarbons with the general formula CnH2n. Alkenes have two hydrogen atoms fewer than the corresponding alkane (with the same number of carbon atoms). The simplest alkene, ethylene (C2H4), with the International Union of Pure and Applied Chemistry (IUPAC) name ethene, is the organic compound produced on the largest scale industrially.Aromatic compounds are often drawn as cyclic alkenes, but their structure and properties are different and they are not considered to be alkenes.
Like a single covalent bond, double bonds can be described in terms of overlapping atomic orbitals, except that, unlike a single bond (which consists of a single sigma bond), a carbon–carbon double bond consists of one sigma bond and one pi bond. This double bond is stronger than a single covalent bond (611 kJ/mol for C=C vs. 347 kJ/mol for C–C) and also shorter, with an average bond length of 1.33 ångströms (133 pm).
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