Bent bond

A banana bond (English banana -bond ) is a special type of covalent atomic bond. It occurs mainly in annular molecules and is accurately described by molecular orbital models.

With normal single bonds two electron clouds overlap ( atomic orbitals ), such that the resulting molecular orbital is on the bond axis. This guarantees maximum overlap and thus the largest energy gain. Because the smallest possible angle between two atomic orbitals is 90 °, this arrangement may not be possible due to geometrical constraints. In such a case, the bonding electron pair spanning the bond axis. The shape of the bond then resembling a banana. Because the bonding electron density is not in the axis between the two linked atoms, orbital overlap is not optimal, and therefore the bonding stronger. This means that compounds with banana bonds are less stable and more reactive. This is also reflected in a larger in comparison with isomeric compounds combustion heat.

Examples of banana bonds

Cyclopropane

The simplest example of a banana bond is to find the cyclopropane C3H6. The molecule is a ring consisting of three atoms. This would lead to a bond angle of 60 °. However, since the electron clouds are located in an sp ³ -hybridized carbon atom in an approximately 109 ° angle, not stretched in the binding assembly is possible. The sp ³ hybrid orbitals are each rotated by about 25 ° from the bond axis. Better approximation provides the Walsh model, which assumes sp ² -hybridized carbons.

Ethene

Two models are discussed for the C = C double bonds. Linus Pauling describes double bonds as consisting of two equivalent bonds, the above presented banana bonds. Erich Hückel proposes, however, that it is composed of a sigma and a pi bond. What explanation is the better, is not yet fully understood, although some theoretical chemists view both representations as equivalent.

Diborane

The compound of diborane ( B2H6 ) is a special case of a banana bond is located. Is a 2- electron -3 center bonding. The two electrons are in a molecular orbital that is delocalized over three atoms.