The old name for alkenes is olefins.
The Origin of the Name "Olefins"
The term "olefins" derives from the Latin words "oleum" (oil) and "fieri" (to make), essentially meaning "oil-forming." This historical nomenclature stems from a significant chemical property observed in the lower members of this class of hydrocarbons. Specifically, when treated with halogens like chlorine or bromine, these compounds readily react to form oily products. For instance, the reaction of ethylene (the simplest alkene) with chlorine produces 1,2-dichloroethane, an oily liquid, which contributed to the group being historically known as "olefins."
Alkenes in Modern Chemistry
In modern chemical nomenclature, based on the systematic rules established by the International Union of Pure and Applied Chemistry (IUPAC), the term "alkenes" is universally preferred. Alkenes are a class of unsaturated hydrocarbons characterized by the presence of at least one carbon-carbon double bond (C=C) in their molecular structure. This double bond provides them with distinct chemical reactivity compared to alkanes, which only contain single bonds.
Key characteristics of alkenes include:
- Unsaturation: The presence of a double bond means they have fewer hydrogen atoms than their corresponding alkanes.
- Reactivity: The double bond is a site of high electron density, making alkenes more reactive than alkanes, especially towards addition reactions.
- Isomerism: Alkenes can exhibit various types of isomerism, including structural isomerism and geometric (cis-trans) isomerism, due to the restricted rotation around the double bond.
Common Examples of Alkenes:
- Ethene (Ethylene): C₂H₄, the simplest alkene, widely used in polymer production (polyethylene) and as a plant hormone.
- Propene (Propylene): C₃H₆, used in the production of polypropylene.
- Butene: C₄H₈, existing in several isomeric forms.
Nomenclature Evolution
The shift from "olefins" to "alkenes" reflects the standardization and systematic approach adopted in chemical nomenclature to ensure clarity and precision. While "olefins" is still occasionally encountered, particularly in industrial contexts, "alkenes" is the official and scientifically accurate term used in academic and research settings.
The following table highlights the transition in naming:
| Feature | Old Name | Current (IUPAC) Name |
|---|---|---|
| Class Name | Olefins | Alkenes |
| Suffix | -ylene | -ene |
| Example | Ethylene | Ethene |
| Origin/Meaning | Oil-forming | Denotes a C=C bond |
This evolution ensures that the name directly conveys structural information about the compound, making the vast field of organic chemistry more organized and understandable. For further details on alkene properties and reactions, you can explore resources on organic chemistry.
