Alkenes are organic molecules that contain at least one carbon-carbon double bond. They are categorized as cis or trans, depending on the configuration. However, E and Z is the official IUPAC nomenclature. Generally, alkene stability increases as the substitution around an alkene increases. The suffix of an alkene is -ene, and alkenes have similar physical properties to alkanes and alkynes. Alkenes have priority over alkanes in nomenclature, and they are extremely common and occur naturally. Alkenes are also used to synthesize a variety of products, including polymers and pharmaceuticals. Alkenes have many different types of reactions, including hydrogen halide addition, hydrogenation, hydration, and halohydrin reactions. Alkenes undergo cleavage reactions that result in aldehydes or ketones. Alkenes are used in the synthesis of medicines and polymers. These syntheses require careful consideration of which reactions may be useful in preparing the desired product.

At A Glance

  • Alkenes are categorized as cis or trans (if there are two groups or identical groups) or by E and Z, which is the official designation of alkene stereochemistry. Stability of alkenes is determined by the degree of substitution of the alkene.
  • In IUPAC (International Union of Pure and Applied Chemistry) nomenclature, alkenes are indicated by changing the suffix from -ane to -ene. A number indicates the location of the double bond (the locant).
  • Alkenes are very similar in physical properties to alkanes.
  • E2 elimination reactions are the main method for preparing alkenes, although under some conditions E1 reactions are useful.
  • Addition reactions are reactions where a reagent adds to an alkene. Addition reactions are the opposite of HX{\rm{H{-}X}} eliminations.
  • Hydration is the process of adding water to an alkene. Hydrogenation is the process of adding hydrogen to an alkene.
  • The halohydrin reaction, syn- or anti-dihydroxylation, carbene reaction, and oxidative cleavage are other types of addition reactions of alkenes.