mesoionic compound

(chemistry) any of a class of compounds having five-membered ring heterocycles (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 polar structure; typically the ring structure contains both positive and negative delocalised charges which cannot be associated with any one ring atom, and the negative charge can also be associated with a conjugated exocyclic atom (typically oxygen, sulfur, or nitrogen).

日本語の意味

メソイオン性化合物：五員環のヘテロ環（またはそのベンゾ誘導体）を有し、環全体で6個のπ電子が共役している化合物。 / この化合物は、正負の電荷が環内（または共役性の環外原子、通常は酸素、硫黄、または窒素）に非局在化して存在し、いずれか一つの共価結合または極性構造で完全には表現できない特徴を持つ。