Interesting little molecule, sydnone. It’s a mesoionic heterocyclic aromatic. In other words, it’s an aromatic ring which is charged both negatively and positively, and both charges are delocalised.

Mesoionic compounds, while effectively neutral overall, cannot be assigned an uncharged structure. In fact, they can’t actually be fully described by any one structure at all. Due to the delocalisation, at least one of the charges tends to fall on two or more different atoms (though the positive charge stays associated with the ring, regardless of the other).

Sydnone’s actually the only one of these compounds I know about, and it’s more of a curiosity than a useful compound. Replace that keto (=O) group with an imine (=NH) though, and you’ll find it in a couple of stimulant drugs (dopamine reuptake inhibitors). Ok, so technically I suppose that means I know about two mesoionic compounds…

Sydnone is also a substituted hydrazine. A nitrogen analog of ethane, hydrazine is commonly used as rocket fuel, and was the US military’s excuse for shooting down a defunkt satellite last year.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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