Conjugated system
In chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

, a conjugated system is a system of connected p-orbitals with delocalized electron
Delocalized electron
In chemistry, delocalized electrons are electrons in a molecule, ion or solid metal that are not associated with a single atom or one covalent bond....

s in compounds with alternating single and multiple bonds, which in general may lower the overall energy of the molecule and increase stability. Lone pair
Lone pair
In chemistry, a lone pair is a valence electron pair without bonding or sharing with other atoms. They are found in the outermost electron shell of an atom, so lone pairs are a subset of a molecule's valence electrons...

s, radicals
Radical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...

 or carbenium ion
Carbenium ion
A carbenium ion is a carbocation of the trivalent and classical type R3C+. It is one of two types of carbocation, the other being a carbonium ion. In older literature a carbocation of the type R3C+ may still be referred to as a carbonium ion, a term that is used now for five-coordinate carbon...

s may be part of the system. The compound may be cyclic, acyclic, linear or mixed.

Conjugation is the overlap of one p-orbital with another across an intervening sigma bond
Sigma bond
In chemistry, sigma bonds are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most clearly defined for diatomic molecules using the language and tools of symmetry groups. In this formal approach, a σ-bond is...

 (in larger atoms d-orbitals can be involved).

A conjugated system has a region of overlapping p-orbitals, bridging the interjacent single bonds.