We do not currently know of any antonyms for mesoionic compound.
The noun mesoionic compound is defined as:
any of a class of compounds having five-membered ringheterocycles (or their benzo derivatives) which possess a sextet of π-electrons in association with the atoms comprising the ring, but which cannot be represented by any one covalent or polarstructure; typically the ring structure contains both positive and negative delocalisedcharges which cannot be associated with any one ring atom, and the negative charge can also be associated with a conjugatedexocyclic atom (typically oxygen, sulfur, or nitrogen).
