Unsaturated hydrocarbons that contain one or more double carbon-carbon bonds in their molecules. In systematic chemical nomenclature alkene names end in the suffix -ene. Alkenes that have only one double bond form a homologous series (the alkene series) starting ethene (ethylene), CH2:CH2, propene, CH3CH:CH2, etc. The general formula is CnH2n. Higher members of the series show isomerism depending on position of the double bond; for example, butene (C4H8) has two isomers, which are (1) but-1-ene (C2H5CH:CH2) and (2) but-2-ene (CH3CH:CHCH3): see formulae. Alkenes can be made by dehydration of alcohols (passing the vapour over hot pumice):RCH2CH2OH – H2O → RCH:CH2 An alternative method is the removal of a hydrogen atom and halogen atom from a haloalkane by potassium hydroxide in hot alcoholic solution:RCH2CH2Cl+KOH → KCl+H2O+RCH:CH2Alkenes typically undergo addition reactions to the double bond. They can be tested for by the Baeyer test. See also hydrogenation; oxo process; ozonolysis; Ziegler process.
RCH2CH2OH – H2O → RCH:CH2
RCH2CH2Cl+KOH → KCl+H2O+RCH:CH2
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