hiilihiilikaksoissidos

Hiilihiilikaksoissidos, or carbon–carbon double bond, is a covalent bond between two carbon atoms that consists of one sigma bond and one pi bond. The sigma bond forms from the end-to-end overlap of sp2 hybrid orbitals on each carbon, while the pi bond arises from side-by-side overlap of the remaining p orbitals. The pi bond lies above and below the plane of the bonded atoms, contributing to the bond’s reactivity.

In terms of geometry, each carbon in a C=C bond is typically sp2 hybridized and adopts a trigonal planar arrangement with bond angles close to 120 degrees. The C=C bond length is about 1.33–1.34 angstroms, and the bond energy is around 600–650 kJ/mol, depending on substituents. Rotation around a carbon–carbon double bond is restricted due to the pi bond, so the bonded carbons cannot freely rotate relative to each other.

The hiilihiilikaksoissidos is a defining feature of alkenes and related unsaturated systems. Its pi component makes the bond more reactive than a single C–C bond, serving as the site for many addition reactions, such as hydrogenation, halogenation, hydrohalogenation, and hydration. Substituted C=C bonds can exhibit geometric isomerism (cis/trans or E/Z) because rotation around the bond is hindered, leading to distinct stereoisomers with different properties.

Applications and relevance include the role of C=C bonds in organic synthesis, polymer chemistry (for example, polymerization of ethene to polyethylene), and the chemistry of natural products and materials. While carbon–carbon double bonds are fundamental to many compounds, their behavior can be influenced by conjugation, substitution, and the surrounding chemical environment.