KekuléStrukturen

Kekulé structures, also known as resonance structures or contributing structures, are a way to represent molecules where electrons are delocalized. They are particularly useful for describing the bonding in molecules and ions that cannot be adequately represented by a single Lewis structure. In such cases, multiple Lewis structures are drawn, each differing in the placement of electrons, particularly double and triple bonds. These individual structures are not considered to exist independently but rather contribute to an overall average structure, the true representation of which is called the resonance hybrid. The arrows used to connect Kekulé structures are double-headed, signifying resonance, and not equilibrium.

The concept of Kekulé structures is named after the German chemist Friedrich August Kekulé, who first proposed this idea to explain the structure of benzene. Benzene was known to have a molecular formula of C6H6, but its reactivity did not align with a structure containing alternating single and double bonds. Kekulé's proposal of two rapidly interconverting structures, a hexagon with alternating single and double bonds that could be drawn in two ways, helped explain its unique stability and reactivity. Modern understanding, using molecular orbital theory, clarifies that the pi electrons in benzene are delocalized over the entire ring, forming a continuous electron cloud, rather than being confined to specific double bonds. Nevertheless, Kekulé structures remain a valuable and widely used tool in organic chemistry for visualizing and predicting the behavior of molecules with delocalized electron systems.