Field of Science

Say that again? Why chemical names tangle on the tongue

Michael Pollan's Food Rules famously advises not eating anything with an ingredient a 3rd grader can't pronounce.  The rule is more about eating closer to the production point, about consuming things that are familiar to 3rd graders (like broccoli and eggs), than it is that chemicals that are hard to pronounce are inherently hazardous, though in some corners it's taken on just that sort of magical thinking.

Why are chemical names so weird looking? Take 2-Methyl-5-(6-methylhept-5-en-2-yl)cyclohexa-1,3-diene for example.  It certainly doesn't sound like anything you would want to eat, but it is just the formal name for the compound that is the main component of ginger oil, and responsible for much of ginger's characteristic bite.  Like crystallized ginger, ginger tea, or a good stir fry?  You've eat this compound in significant quantities.

Chemical names can look like alphabet soup, but they are a way for chemists to paint a compact picture of the structure, or at least to point out key structural features.  Why is it so important to know what a molecule looks like?  The structure of a chemical is what determines its behavior, how it will react, in the body and in the environment.  It's key to understanding how things work on the molecular level:  structure determines function.  Period.

Formal chemical names, called IUPAC names (for the International Union of Pure and Applied Chemists, the body that decides on everything from what new elements will be called to the standards for drawing molecules), are in fact a code from which the full structure of the molecule can be unraveled.  Most of the time chemists call chemicals by a common name, which also gives clues to the structure, though not so many that the molecule could be unambiguously drawn.

So back to 2-Methyl-5-(6-methylhept-5-en-2-yl)cyclohexa-1,3-diene, which looks like


The "methyl"s (METH-ill) in the name refer to a CH3 group. What, you don't see any CH3's here?  This is a chemical line structure, where each intersection point (or end of a line) is a carbon atom, and the hydrogen atoms have almost all been left off.  A chemist sees this structure as 

with the methyls at either end.  The little red dots count off a seven membered chain, the "hept" in the name. The "cyclohexa" (sigh-clo-HEX-uh) points to a six membered ring, while "diene" (DIE-een) means it has two double bonds in it. The numbers tell you where to attach methyls and draw the double bonds.  The little "2-yl" (too-ill) means the seven membered chain is linked to the six membered ring at the second carbon in line.

So these tangled names to a chemist are codes, and once you can read the code, even a bit, you can begin to see a molecule taking shape in your mind when you read its name.

This pronounces as 2-METH-ill / 5, 6-METH-ill-hept 5 een 2 ill cyclo HEX uh 1 3 DIE-een.

There's probably a reason this is better known as zingiberene, which suggests its common origin (ginger or zingiber), but not much about its structure.

1 comment:

  1. Thank you for sharing. Hope to hear more from you.

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