SigmaBindungen

Sigma bindings, often denoted as σ bindings, are the strongest type of covalent chemical bond. They are formed by the direct overlap of atomic orbitals along the internuclear axis, meaning the electron density is concentrated between the two bonded atoms. This head-on overlap is characteristic of sigma bindings.

Sigma bindings can form between various types of atomic orbitals, including s-s, s-p, and p-p overlaps. For instance, the hydrogen molecule (H2) features a sigma binding formed by the overlap of two 1s atomic orbitals. In methane (CH4), the carbon-hydrogen bonds are all sigma bindings resulting from the overlap of a carbon sp3 hybrid orbital with a hydrogen 1s orbital.

A key feature of sigma bindings is their rotational symmetry around the bond axis. This allows for free rotation of the bonded atoms without breaking the bond, provided there are no steric hindrances or other interactions. This free rotation is fundamental to the conformational flexibility of many organic molecules.

Single covalent bonds are always sigma bindings. When multiple bonds exist between two atoms, such as a double or triple bond, one of these bonds is a sigma binding, and the others are pi bindings. Pi bindings are formed by the sideways overlap of atomic orbitals, with electron density located above and below the internuclear axis. The presence of a sigma binding provides the structural backbone for molecules, while pi bindings contribute to their reactivity and rigidity.