CCkaksoissidos

CCkaksoissidos, or the carbon–carbon double bond (C=C), is a covalent bond between two carbon atoms formed by one sigma bond and one pi bond. It is the defining feature of alkenes and a key site of reactivity in organic chemistry.

In terms of structure, each carbon in a C=C is typically sp2 hybridized, resulting in a trigonal planar arrangement with bond angles near 120 degrees. The pi bond arises from sideways overlap of the remaining p orbitals, which is weaker than the sigma component and also restricts rotation about the bond. This restricted rotation gives rise to geometric isomerism in many alkenes.

Typical physical parameters include a C=C bond length of about 1.33 Å and a bond dissociation energy around 610 kJ/mol, though these values vary with substituents. The barrier to rotation around a C=C bond is substantial, on the order of tens of kilojoules per mole, effectively locking the double bond in place under normal conditions.

Geometrically, alkenes can exhibit cis/trans (or E/Z) isomerism depending on the groups attached to each carbon of the double bond. This stereochemistry affects physical properties and reactivity and is a central consideration in synthesis and materials science.

Reactivity centers around the double bond as a site for addition reactions, including hydrogenation, halogenation, hydrohalogenation, and hydration. These reactions convert alkenes into a wide range of products and are foundational to polymerization processes, industrial chemistry, and the synthesis of complex organic molecules. Spectroscopically, C=C stretches appear in the IR around 1650 cm-1, and vinyl protons show characteristic signals in the 4.5–6.5 ppm region in NMR.