2012: Advent Chemistry: Arsole

by on December 23, 2012

Today, it’s time for something a bit silly.
The structure of arsole, a five-membered ring of carbon and arsenic with two double bonds.
This is the second-best pun in the whole of chemistry: arsole, pronounced exactly the way you think. Arsole is actually its correct systematic name. I mean, it wasn’t called that for a joke. If you apply the international naming rules, arsole is what you get for this molecule.

The ‘ars’ comes from arsenic, symbol As. Arsenic is of course poisonous, although not actually very poisonous. You need quite large doses to kill someone. It’s usually classified as a metal, but in this molecule it forms covalent bonds. Covalent bonds aren’t the preferred kind of activity for metals, which tend to favour ionic or coordination interactions. Arsenic, if you look at the periodic table, sits in the borderlands between the transition metals (iron, copper, nickel and so on) and the nonmetals (carbon, oxygen, nitrogen and their ilk). Like silicon, it’s a halfway house and can behave like either kind of thing.

The ‘ole’ part of the name comes from the double bond. It’s short for olefin, meaning ‘containing a double bond’. Alkenes and benzene rings, as we’ve seen before, contain double bonds, but because of the simplicity of them – they only have carbon in the ring – they can be more precisely classified than olefins. Alkenes are olefins, but not all olefins are alkenes.

The best pun in chemistry is a derivative of arsole in which a benzene ring is fused to one side: benzarsole.

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