mesoionic
Mesoionic refers to a class of heterocyclic compounds and related ions in which a pronounced internal charge separation is intrinsic to the ring system. The overall molecule is neutral, but several resonance forms place positive and negative charges on different ring atoms in a way that cannot be represented by a single neutral Lewis structure. This leads to a dipolar character that is delocalized over the ring and, in many cases, to pronounced reactivity patterns.
A defining feature of mesoionic systems is that the charge separation is embedded within the ring rather
Well-known members of the mesoionic family include sydnones and munchnones, which are five-membered rings that exhibit
Historically, the concept emerged from physical organic chemistry as researchers explored unusual charge distributions in heterocycles.