The formal positive charge is associated with the ring atoms and the formal negative charge is associated either with ring atoms or an
exocyclicnitrogen or other atom.[3] These compounds are stable
zwitterionic compounds[4] and belong to nonbenzenoid
aromatics.[5]
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. 39 (11): 1581–1583.
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): 3368–3372.
doi:
10.1021/jo00821a022.