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Mesoionic chemical compounds or mesoionic compounds are dipolar five membered heterocyclic compounds in which both the negative and the positive charges are delocalized.[1][2] A completely uncharged structure cannot be written and mesoionic compounds cannot be represented satisfactorily by any one mesomeric structure.[2] Mesoionic compounds are a subclass of betaines.[2] Examples are sydnones and sydnone imines (e.g. the stimulant mesocarb), and münchnones.[1][2][3]

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 atom.[4] These compounds are stable zwitterionic compounds[5] and belong to nonbenzenoid aromatics.[6]


  1. ^ a b Bhosale, Sachin K.; Deshpande, Shreenivas R.; Wagh, Rajendra D. (2012). "Mesoionic sydnone derivatives: An overview". Journal of Chemical and Pharmaceutical Research 4 (2): 1185–99. 
  2. ^ a b c d IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "mesoionic compounds".
  3. ^ Ollis, W.David; Stanforth, Stepher P.; Ramsden, Christopher A. (1985). "Heterocyclic mesomeric betaines". Tetrahedron 41 (12): 2239. doi:10.1016/S0040-4020(01)96625-6. 
  4. ^ "SYDNONES". [page needed]
  5. ^ "Seeking Mesoionic Compounds". 
  6. ^ Badami, Bharati V (2006). "Mesoionic compounds". Resonance 11 (10): 40. doi:10.1007/BF02835674. 

Further reading[edit]

  • Senff-Ribeiro, A; Echevarria, A; Silva, EF; Franco, CR; Veiga, SS; Oliveira, MB (2004). "Cytotoxic effect of a new 1,3,4-thiadiazolium mesoionic compound (MI-D) on cell lines of human melanoma". British journal of cancer 91 (2): 297–304. doi:10.1038/sj.bjc.6601946. PMC 2409799. PMID 15199390. 
  • Mickleburgh, I; Geng, F; Tiley, L (2009). "Mesoionic heterocyclic compounds as candidate messenger RNA cap analogue inhibitors of the influenza virus RNA polymerase cap-binding activity". Antiviral chemistry & chemotherapy 19 (5): 213–8. PMID 19483269. 
  • Cadena, Silvia M.S.C.; Carnieri, Eva G.S.; Echevarria, Aurea; De Oliveira, Maria Benigna Martinelli (2002). "Interference of MI-D, a new mesoionic compound, on artificial and native membranes". Cell Biochemistry and Function 20 (1): 31–7. doi:10.1002/cbf.932. PMID 11835268. 
  • Papageorgiou, M.; Kokkou, S. C.; Rentzeperis, P. J.; Tsoleridis, C. (1983). "Structure of the mesoionic compound N-[1-methyl-3-(p-tolyl)-4-(1,2,3-triazolio)]acetamidate (MMTAT), C12H14N4O". Acta Crystallographica Section C Crystal Structure Communications 39 (11): 1581. doi:10.1107/S0108270183009348. 
  • Potts, K. T.; Husain, Syeda (1971). "Mesoionic compounds. XIV. Mesoionic compounds of the imidazole series". The Journal of Organic Chemistry 36 (22): 3368. doi:10.1021/jo00821a022.