Definition
Alkenes are organic compounds which contain double bonds between carbon atoms (C=C). Alkenes are hydrocarbons, meaning that they consist exclusively of carbon and hydrogen atoms. They are also called unsaturated compounds. This is in contrast to the saturated ones, which contain only single bonds (C-C). Alkenes can be linear (acyclic) or cyclic. Cycloalkenes are, for example, cyclohexene or cyclopentene. Aromatics, on the other hand, are not counted among the alkenes.
Nomenclature
Alkenes are named with the suffix -en. The suffix -ylene is also used for trivial names, for example ethylene instead of ethene or propylene instead of propene. Polyunsaturated alkenes carry the suffix -diene, -triene, -tetraene, etc.
Representative
A selection of alkenes:
- Ethene
- Propene
- 1-Butene
- 1-pentene
- 1-Witches
- 1-Hepts
- 1-Nones
- 1-Decen
Other:
- Beta-carotene
- Isoprene, isoprenoids
- Squalene
Properties
- Due to the absence of polar groups such as a hydroxyl group, alkenes are lipophilic and sparingly soluble in water. They dissolve in organic solvents. Alkenes therefore also have comparatively low boiling points.
- Alkenes are more reactive than the corresponding alkanes.
- Double bonds are shorter and stronger than single bonds.
- Like alkanes, alkenes exist as gases, liquids, or semisolids to solids, depending on their size.
- Because the double bond is not rotatable, cis-trans isomers are formed.
- The boiling points are comparable to those of alkanes.
Reactions
- Typical reactions of alkenes are addition reactions, for example with water, halogens (halogenation) or hydrochloric acid (hydrohalogenation).
- Hydrogenation with hydrogen and a catalyst such as platinum, palladium or nickel.
- Isomerization (photoisomerization)
- Polymerization
- Oxidation
- Burns
In pharmacy
Countless active pharmaceutical ingredients and excipients contain double bonds.
