σ Bond

Definition

A σ bond is a type of covalent chemical bond formed by the head-on overlap of atomic orbitals, resulting in an increased electron density along the internuclear axis. This type of bond is essential in the understanding of organic chemistry concepts such as benzyne and sigmatropic rearrangements.

5 Must Know Facts For Your Next Test

1. σ bonds are the strongest type of covalent bonds, providing the primary framework for organic molecules.
2. In benzyne, the formation of a σ bond is a key step in the generation of the reactive intermediate.
3. Sigmatropic rearrangements involve the migration of a σ bond to a new position within the molecule.
4. The overlap of s and p orbitals can lead to the formation of sp, sp², and sp³ hybridized σ bonds.
5. The strength and directionality of σ bonds are crucial in determining the overall stability and reactivity of organic compounds.

Review Questions

• Explain the role of σ bonds in the formation of the benzyne intermediate.
  • In the context of benzyne, the formation of a σ bond is a key step in the generation of the reactive intermediate. Benzyne is formed by the removal of a halogen atom from a halogenated benzene ring, creating a highly reactive cyclic alkene with a triple bond. The formation of this triple bond involves the breaking of a σ bond, which is then replaced by the creation of a new σ bond in the benzyne structure. This σ bond, along with the π bonds, contributes to the overall stability and reactivity of the benzyne intermediate.
• Describe how σ bonds are involved in sigmatropic rearrangements.
  • Sigmatropic rearrangements are pericyclic reactions that involve the migration of a σ bond to a new position within the molecule. In these rearrangements, the σ bond being migrated is typically part of a larger π system, such as in allylic or benzylic compounds. The movement of the σ bond is accompanied by the simultaneous formation of new σ and π bonds, resulting in the rearrangement of the molecular structure. The directionality and strength of the σ bonds play a crucial role in determining the feasibility and outcome of these sigmatropic rearrangement reactions.
• Analyze the relationship between σ bonds, hybridization, and the stability of organic compounds.
  • The formation of σ bonds is closely tied to the concept of hybridization, where the mixing of atomic orbitals results in the creation of new hybrid orbitals that can participate in covalent bond formation. The type of hybridization (sp, sp², or sp³) determines the geometry and directionality of the σ bonds, which in turn affects the overall stability and reactivity of organic compounds. For example, sp³ hybridized σ bonds in alkanes are more stable than the sp² hybridized σ bonds in alkenes, which are more reactive due to the presence of π bonds. Understanding the relationship between σ bonds, hybridization, and stability is crucial in predicting and explaining the behavior of organic molecules, particularly in the context of reactions such as benzyne formation and sigmatropic rearrangements.

Related terms

π Bond: A π bond is a type of covalent bond formed by the side-to-side overlap of atomic orbitals, resulting in increased electron density above and below the internuclear axis.

Hybridization: Hybridization is the mixing of atomic orbitals to form new hybrid orbitals, which can participate in the formation of σ and π bonds.

Aromaticity: Aromaticity is a property of certain cyclic compounds, such as benzene, where the π electrons are delocalized, contributing to the stability of the molecule.