alkeenideks

Alkeenideks (Estonian for alkenes) are a class of hydrocarbons that contain at least one carbon–carbon double bond. In acyclic alkenes the general formula is CnH2n, while cycloalkenes have the formula CnH2n−2. The double bond is formed by sp2-hybridized carbons, giving planar geometry around the bond and restricting rotation. When a double bond carries two different substituents on each carbon, alkenes can exhibit geometric (cis/trans or E/Z) isomerism.

Alkenes are more chemically reactive than alkanes due to the carbon–carbon double bond, and they participate in a wide range of addition reactions. Common transformations include hydrogenation (adding H2 to form alkanes), halogenation (adding X2), hydrohalogenation (adding HX), and hydration (adding H2O in the presence of acid to yield alcohols). They can also undergo polymerization, producing polyalkenes such as polyethylene and polypropylene. Industrially, many alkenes are prepared from petrochemical processing and serve as important building blocks for plastics, solvents, and fine chemicals.

Nomenclature follows substitutive rules: the longest carbon chain containing the double bond is selected, the suffix -ene is used to indicate the double bond, and the bond's position is numbered to give the lowest possible locant. If a double bond is substituted with different groups on each carbon, stereoisomerism (E/Z) may arise. Physical properties vary with chain length and substitution; small alkenes are gases or liquids at room temperature, while larger ones are liquids or solids. Alkeenideks are central to organic synthesis and industrial chemistry, underpinning many polymers and chemical feedstocks.