Carbon-Carbon Double Bond

Definition

A carbon-carbon double bond is a covalent chemical bond in which two carbon atoms share four electrons, with two pairs of electrons forming the bond. This type of bond is a fundamental structural feature in many organic compounds and is central to understanding the properties and reactivity of alkenes, a class of unsaturated hydrocarbons.

5 Must Know Facts For Your Next Test

1. The carbon-carbon double bond is characterized by the presence of two pairs of shared electrons between the two carbon atoms, resulting in a shorter and stronger bond compared to a single carbon-carbon bond.
2. The carbon-carbon double bond is planar, with the four atoms (the two carbon atoms and the two atoms or groups attached to them) lying in the same plane, due to the sp2 hybridization of the carbon atoms.
3. The presence of a carbon-carbon double bond in a molecule introduces the possibility of geometric isomerism, where the relative positions of the substituents around the double bond can lead to the formation of cis and trans (or Z and E) isomers.
4. Alkenes, a class of organic compounds containing at least one carbon-carbon double bond, exhibit characteristic reactivity, such as undergoing electrophilic addition reactions, which is important in the context of the Wittig reaction.
5. The carbon-carbon double bond is a key structural feature in many biologically important molecules, such as lipids, steroids, and carotenoids, and plays a crucial role in their properties and functions.

Review Questions

• Explain the role of sp2 hybridization in the structure and geometry of the carbon-carbon double bond.
  • The carbon-carbon double bond is formed by the sp2 hybridization of the carbon atoms. In sp2 hybridization, the carbon atom's s orbital and two of its p orbitals combine to form three equivalent sp2 hybrid orbitals, which are arranged in a trigonal planar geometry. This sp2 hybridization allows the carbon atoms to form the two sigma bonds and one pi bond that make up the carbon-carbon double bond, resulting in a planar structure with the four atoms (the two carbon atoms and the two atoms or groups attached to them) lying in the same plane.
• Describe how the carbon-carbon double bond is represented in the molecular orbital theory and how this relates to the stability and reactivity of alkenes.
  • According to the molecular orbital theory, the carbon-carbon double bond is formed by the overlap of the carbon atoms' sp2 hybrid orbitals to create a sigma bond, and the overlap of the remaining p orbitals to create a pi bond. The presence of this pi bond, in addition to the sigma bond, contributes to the stability of the carbon-carbon double bond. However, the pi bond is weaker than the sigma bond and can be more easily broken, which accounts for the characteristic reactivity of alkenes, such as their ability to undergo electrophilic addition reactions. The molecular orbital theory provides a deeper understanding of the electronic structure and bonding in molecules containing carbon-carbon double bonds, which is crucial for predicting and explaining their chemical properties and reactivity.
• Analyze the significance of the carbon-carbon double bond in the context of the Wittig reaction, a nucleophilic addition reaction involving phosphorus ylides.
  • The carbon-carbon double bond is a central feature in the Wittig reaction, a powerful organic transformation used to synthesize alkenes. In the Wittig reaction, a phosphorus ylide, a nucleophilic species containing a carbon-phosphorus double bond, reacts with a carbonyl compound (an aldehyde or ketone) to form a new carbon-carbon double bond. The reactivity of the carbon-carbon double bond in the product alkene is influenced by the electronic and steric factors introduced by the substituents, which can lead to the formation of specific geometric isomers (cis or trans). Understanding the properties and reactivity of the carbon-carbon double bond is crucial for predicting the outcome and controlling the stereochemistry of the Wittig reaction, making it a valuable tool in organic synthesis.

Related terms

sp2 Hybridization: A type of orbital hybridization where a carbon atom's s orbital and two of its p orbitals combine to form three equivalent sp2 hybrid orbitals, which are responsible for the trigonal planar geometry of molecules containing carbon-carbon double bonds.

Molecular Orbital Theory: A model that describes the formation of chemical bonds by the combination of atomic orbitals to create new molecular orbitals, which can be used to explain the stability and reactivity of molecules with carbon-carbon double bonds.

Alkenes: Unsaturated hydrocarbons that contain at least one carbon-carbon double bond, which gives them unique chemical and physical properties compared to alkanes.