An alkene is a type of hydrocarbon characterized by the presence of a carbon-carbon double bond. These compounds are classified as unsaturated hydrocarbons since they contain at least one double bond between carbon atoms. The double bond is composed of a sigma bond and a pi bond, which contribute significantly to the reactivity of alkenes. The general molecular formula for alkenes is given by $C_nH_{2n}$, where $n$ represents the number of carbon atoms in the molecule.

Alkenes are typically formed through elimination reactions, which involve the removal of a leaving group from a molecule, resulting in the establishment of a double bond. A common type of elimination reaction is dehydrohalogenation, which occurs with alkyl halides and involves the removal of a hydrogen halide ($H-X$). This reaction is facilitated by a strong base, such as sodium hydroxide ($NaOH$), which abstracts the acidic hydrogen from the alkyl halide.

Another method for synthesizing alkenes is through dehydration reactions. These reactions entail the removal of a water molecule from an alcohol, and they are usually catalyzed by a strong acid, such as concentrated sulfuric acid ($H_2SO_4$). The acid protonates the alcohol, generating a good leaving group that facilitates the elimination of water.

Alkenes play a crucial role as intermediates in organic synthesis and are utilized in the production of a diverse array of chemicals, including plastics, solvents, and pharmaceuticals. Furthermore, they are significant in biological systems, where they contribute to the biosynthesis of fatty acids and other natural products.