{{Short description|Molecules with dipolar heterocyclic structures and delocalized charges}} thumb|400px|Sydnone structures are mesoionic In chemistry, '''mesoionic compounds''' are one in which a heterocyclic structure is dipolar and where both the negative and the positive charges are 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 mesomeric structure.<ref name="GoldBookRef"/> Mesoionic compounds are a subclass of betaines.<ref name="GoldBookRef"/> Examples are sydnones and sydnone imines (e.g. the stimulant mesocarb), münchnones,<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 carbenes.
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 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 zwitterionic compounds<ref>{{cite web |url=https://www.innocentive.com/ar/challenge/9932814 |title=Seeking Mesoionic Compounds}}</ref> and belong to nonbenzenoid aromatics.<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
== 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