Molecular Monday: Why Is It Called Octane?

I’m not really a car guy, so I’ve never given much thought to octane before, but since I’ve challenged myself to learn about organic chemistry, I was bound to run into this particular hydrocarbon eventually.

And I was particularly surprised (and amused) when I found out how octane got its name.

Hydrocarbons are chemicals composed exclusively of hydrogen and carbon atoms. For the sake of simplicity, let’s ignore the hydrogen atoms (chemists often do) and look at four of the simplest hydrocarbons:

• Methane: has one carbon atom.
• Ethane: has two carbon atoms.
• Propane: has three carbon atoms.
• Butane: has four carbon atoms.

These four chemicals are members of a subcategory of hydrocarbons called alkanes (or sometimes paraffins). They were all named before their chemical structures were well understood, but for alkanes larger than butane, the naming system gets much easier to follow (assuming you’re familiar with Greek numbers).

• Pentane: five carbon atoms.
• Hexane: six carbon atoms.
• Heptane: seven carbon atoms.
• Octane: eight carbon atoms.
• Novane: nine carbon atoms.
• Decane: ten carbon atoms.

So that’s why we call it octane. It’s the same “oct-” that you see in octagon or octopus. In not sure this is a super important chemistry fact; it’s just something that’ll make me smile next time I’m filling up my car at the gas station.

P.S.: After decane comes undecane, dodecane, tridecane, tetradecane….

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Today’s post is part of an ongoing series called Molecular Mondays. I’ve challenged myself to learn as much as I can about chemistry, and so every other Monday I try to share some interesting chemistry tidbit here on my blog.