The Secret Language of Chemists: Why does butter make us think of four?

Butter and why it means "four" to chemists.
c. Michelle Shrank CC license

Every time I take a stick of butter out of the 'fridge I think of the number four.  No, it's not some odd form of synethesia, but a side effect of being a chemist.

Names of molecules and their structures are (sometimes) related to each other.  You can think of organic molecules (molecules that are principally built from carbon, hydrogen, oxygen and nitrogen) are constructed like Lego buildings.  There are blocks, each block has a name and you click them into place (that last isn't so simple in practice) to build a molecule. So knowing the secret language of chemistry gives you a window into the structure, which in turn is a clue how the molecule works and what it might be good for.

So why does butter make a chemist think of four?  The stem but — pronounced like "butte" the land formation  —  is used to indicate a four carbon building block.  It is a back-formation from butyric acid, responsible for the smell of rancid butter, which has four carbons in it.  (Butane, a flammable liquid used in lighters, is a four carbon chain.)

The rest of the secret code:

meth- 1 carbon
another back-formation, this time from methanol (wood alcohol) from the Greek root for wine (μέθυ ≡ methy)

eth- 2 carbons
from the Greek, ether, the uppermost reaches of the atmosphere; as seen in ethylene (the sweet smelling flammable gas produced by ripening fruit, particularly bananas.  It's technically a hormone!)

prop- 3 carbons
This one also comes from the Greek (surprise!) for proto and fat, as propionic acid was the first "fatty acid" (acid molecules that also behave like fats or oils); propane gas used in stoves and grills has three carbon atoms and 8 hydrogen atoms per molecule.

but- 4 carbons
From the rancid butter!

after four the prefixes are derived directly from the numbers in the chain
pent- 5
hex- 6
hept- 7
oct- 8
non-  9
dec-10
undec- 11
dodec- 12

So when you see references to the food additive BHA, which stands for butylated hydroxyanisole, one thing you can say about it is that it has a four-carbon unit in it somewhere.  Though, I admit, that's not much help in answering the important questions: What does it do, and how will affect me?