Delocalized electron

In chemistry, delocalized electrons are electrons in a molecule that do not belong to a single atom or a covalent bond. Delocalized electrons are part of a pi electron system that extends over several adjacent atoms. Delocalized electrons can be found in Conjugated systems of double bonds and in aromatic systems.

In the simple aromatic ring benzene the delocalization of six pi electrons electrons over the whole ring is often indicated by the circle:

Alternatively, all possible mesomeric structures can be drawn inside square brackets separated by double arrows. This style should be used for polycyclic aromatic rings :

Another example of a delocalized electron is the carboxylic acid. When put in an aqueous solution, the alcohol group releases a hydrogen cation and the electrons delocalize between the two oxygens.

Delocalized electrons are important to take into account for several reasons. One, an expected chemical reaction may not occur because the electrons delocalize to a more stable configuration, resulting in a reaction that happens at a different location.

An example is trying to attach a 1-chloro-2-methyl-propane to a benzene ring, but carbocation chemistry results in a tert-butyl group.