A carbon-carbon double bond (C=C) is a fundamental structural feature in organic chemistry. It consists of two carbon atoms that share two pairs of electrons through a sigma (σ) bond and a pi (π) bond, resulting in a strong and rigid connection between the two carbons.

Here are some key points about the carbon-carbon double bond:

1. Bonding: The carbon-carbon double bond consists of a sigma (σ) bond and a pi (π) bond. The sigma bond results from head-on overlap of two hybridized orbitals from each carbon atom. The pi bond arises from the side-to-side overlap of two unhybridized p orbitals perpendicular to the sigma bond.
2. Hybridization: Carbon atoms in a double bond typically undergo sp² hybridization. One of the carbon atom’s three sp² hybrid orbitals forms the sigma bond with the corresponding orbital on the other carbon atom. The remaining two sp² hybrid orbitals form sigma bonds with hydrogen atoms or other groups.
3. Geometry: The arrangement of atoms around a carbon-carbon double bond is trigonal planar, with bond angles of approximately 120 degrees. This geometry allows for efficient pi bond overlap.
4. Pi Bond: The pi bond is weaker and less directional than the sigma bond. It involves the overlap of two parallel p orbitals, creating a region of electron density above and below the plane of the carbon atoms.
5. Conjugation: Conjugated systems involve alternating single and multiple bonds along a chain of atoms. The presence of pi electrons in conjugated systems contributes to their unique reactivity and stability.
6. Reactivity: Carbon-carbon double bonds are more reactive than single bonds due to the presence of pi electrons. They can participate in various chemical reactions, such as electrophilic addition, nucleophilic addition, and polymerization.
7. Isomerism: The presence of a double bond can give rise to geometric isomerism (cis-trans isomerism) if two different groups are attached to each carbon atom in the double bond.
8. Unsaturated Compounds: Molecules containing carbon-carbon double bonds are often referred to as unsaturated compounds because they have fewer hydrogen atoms than their saturated counterparts (alkanes).
9. Pi Bond Rotation: The pi bond prevents free rotation around the carbon-carbon double bond, resulting in restricted movement.
10. Physical Properties: Molecules with carbon-carbon double bonds may have different physical properties (e.g., boiling points, melting points, density) compared to alkanes with only single bonds.

Carbon-carbon double bonds are central to the structure and reactivity of many organic compounds, playing a crucial role in the diversity of organic chemistry and the development of new materials and drugs.