# Mesoionic compounds

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{{Short description|Molecules with dipolar heterocyclic structures and delocalized charges}}
thumb|400px|Sydnone structures are mesoionic
In [chemistry](/source/chemistry), '''mesoionic compounds''' are one in which a [heterocyclic](/source/heterocyclic_compounds) structure is [dipolar](/source/dipolar_compound) and where both the negative and the positive [charge](/source/charge_(physics))s are [delocalized](/source/delocalized).<ref name="GoldBookRef">{{GoldBookRef | file = M03842 | title = mesoionic compounds}}</ref> A completely uncharged structure cannot be written and mesoionic compounds cannot be represented satisfactorily by any one [mesomer](/source/resonance_(chemistry))ic structure.<ref name="GoldBookRef"/> Mesoionic compounds are a subclass of [betaines](/source/betaines).<ref name="GoldBookRef"/> Examples are [sydnone](/source/sydnone)s and [sydnone imine](/source/sydnone_imine)s (e.g. the [stimulant](/source/stimulant) [mesocarb](/source/mesocarb)), [münchnone](/source/m%C3%BCnchnone)s,<ref name="GoldBookRef"/><ref>{{cite journal |doi=10.1016/S0040-4020(01)96625-6 |title=Heterocyclic mesomeric betaines |year=1985 |last1=Ollis |first1=W.David |last2=Stanforth |first2=Stepher P. |last3=Ramsden |first3=Christopher A. |journal=Tetrahedron |volume=41 |issue=12 |pages=2239–2329}}</ref> and [mesoionic carbene](/source/mesoionic_carbene)s.

The formal positive charge is associated with the ring atoms and the formal negative charge is associated either with ring atoms or an [exocyclic](/source/exocyclic) [nitrogen](/source/nitrogen) or other atom.<ref>{{cite web |url=http://shodhganga.inflibnet.ac.in/bitstream/10603/3033/7/07_chapter%201.pdf |title=SYDNONES}}{{page needed|date=September 2013}}</ref> These compounds are stable [zwitterion](/source/zwitterion)ic compounds<ref>{{cite web |url=https://www.innocentive.com/ar/challenge/9932814 |title=Seeking Mesoionic Compounds}}</ref> and belong to nonbenzenoid [aromatic](/source/aromatic)s.<ref>{{cite journal |doi=10.1007/BF02835674 |title=Mesoionic compounds |year=2006 |last1=Badami |first1=Bharati V |journal=Resonance |volume=11 |issue=10 |pages=40–48}}</ref>

== See also ==
* [Mesomeric betaine](/source/Mesomeric_betaine)

== References ==
{{reflist}}

== Further reading ==
* {{cite journal |pmid=15199390 |year=2004 |last1=Senff-Ribeiro |first1=A |last2=Echevarria |first2=A |last3=Silva |first3=EF |last4=Franco |first4=CR |last5=Veiga |first5=SS |last6=Oliveira |first6=MB |title=Cytotoxic effect of a new 1,3,4-thiadiazolium mesoionic compound (MI-D) on cell lines of human melanoma |volume=91 |issue=2 |pages=297–304 |doi=10.1038/sj.bjc.6601946 |pmc=2409799 |journal=British Journal of Cancer}}
* {{cite journal |pmid=19483269 |year=2009 |last1=Mickleburgh |first1=I |last2=Geng |first2=F |last3=Tiley |first3=L |title=Mesoionic heterocyclic compounds as candidate messenger RNA cap analogue inhibitors of the influenza virus RNA polymerase cap-binding activity |volume=19 |issue=5 |pages=213–8 |journal=Antiviral Chemistry & Chemotherapy |doi=10.1177/095632020901900504|doi-access=free }}
* {{cite journal |doi=10.1002/cbf.932 |title=Interference of MI-D, a new mesoionic compound, on artificial and native membranes |year=2002 |last1=Cadena |first1=Silvia M.S.C. |last2=Carnieri |first2=Eva G.S. |last3=Echevarria |first3=Aurea |last4=De Oliveira |first4=Maria Benigna Martinelli |journal=Cell Biochemistry and Function |volume=20 |pages=31–7 |pmid=11835268 |issue=1|doi-access=free }}
* {{cite journal |doi=10.1107/S0108270183009348 |title=Structure of the mesoionic compound ''N''-[1-methyl-3-(''p''-tolyl)-4-(1,2,3-triazolio)]acetamidate (MMTAT), C12H14N4O |year=1983 |last1=Papageorgiou |first1=M. |last2=Kokkou |first2=S. C. |last3=Rentzeperis |first3=P. J. |last4=Tsoleridis |first4=C. |journal=Acta Crystallographica Section C |volume=39 |issue=11 |pages=1581–1583}}
* {{cite journal |doi=10.1021/jo00821a022 |title=Mesoionic compounds. XIV. Mesoionic compounds of the imidazole series |year=1971 |last1=Potts |first1=K. T. |last2=Husain |first2=Syeda |journal=The Journal of Organic Chemistry |volume=36 |issue=22 |pages=3368–3372}}

Category:Heterocyclic compounds
Category:Zwitterions
Category:Aromatic compounds

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Adapted from the Wikipedia article [Mesoionic compounds](https://en.wikipedia.org/wiki/Mesoionic_compounds) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Mesoionic_compounds?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.