Mesoionic chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

s are dipolar five- or six- membered heterocyclic compounds in which both the negative and the positive charge

Charge (physics)

In physics, a charge may refer to one of many different quantities, such as the electric charge in electromagnetism or the color charge in quantum chromodynamics. Charges are associated with conserved quantum numbers.-Formal definition:...

s are delocalized. A completely uncharged structure cannot be written and mesoionic compounds cannot be represented satisfactorily by any one mesomer

Resonance (chemistry)

In chemistry, resonance or mesomerism is a way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis formula...

ic structure.

The formal positive charge is associated with the ring atoms and the formal negative charge is associated either with ring atoms or an exocyclic nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 atom.

Mesoionic compounds are a subclass of betaines

Betaines

A betaine in chemistry is any neutral chemical compound with a positively charged cationic functional group such as an quaternary ammonium or phosphonium cation which bears no hydrogen atom and with a negatively charged functional group such as a carboxylate group which may not be adjacent to the...

. Examples are sydnone

Sydnone

Sydnone is a mesoionic heterocyclic aromatic chemical compound. A sydnone imine in which the keto group of sydnone has been replaced with an imino group can be found as a substructure in the stimulant drugs feprosidnine and mesocarb.- Discovery :...

s and sydnone imine

Sydnone imine

Sydnone imine is a mesoionic heterocyclic aromatic chemical compound. Sydnone imine is the imine of sydnone where the keto functional group of sydnone has been replaced with an imine group. A sydnone imine substructure can be found in the stimulant drugs feprosidnine and mesocarb and the...

s (e.g. the stimulant

Stimulant

Stimulants are psychoactive drugs which induce temporary improvements in either mental or physical function or both. Examples of these kinds of effects may include enhanced alertness, wakefulness, and locomotion, among others...

 mesocarb

Mesocarb

Mesocarb is a stimulant drug which was developed in the USSR in the 1970s. It has been shown to act as a dopamine reuptake inhibitor which is slower acting but longer lasting and less neurotoxic than dextroamphetamine....

), and münchnones

Münchnone

Münchnone is a mesoionic heterocyclic aromatic chemical compound.- Other Names :In addition to the trivial name münchnone, this molecule has also been referred to as a:* muenchnone* munchnone * 1,3-oxazolium-5-oxide...

.