What's in a Name? How Chemicals Get Their Names

If you look at the label on your ice cream or shampoo, you're bound to find some words that seem like unpronounceable gibberish. Hexadecanoic acid? 5-Methyl-2-(propan-2-yl)cyclohexan-1-ol? What does it mean?!

In actuality, scientists use these names in order to precisely identify a molecule. Each part of the name refers to a different part of the molecule's structure, so even if a scientist has never heard of or seen the molecule before, they can easily draw it based solely on its name. Every organic compound has one of these International Union of Pure and Applied Chemistry (IUPAC) names, even if they have common household names like "palm oil" (a.k.a. hexadecanoic acid) or "mint extract" (a.k.a. 5-Methyl-2-(propan-2-yl)cyclohexan-1-ol) as well. With a little practice, anyone can read an organic compound's IUPAC name and know exactly what the compound is made up of.

The prefix of the name determines how long the carbon chain is. These prefixes are often easy to determine because they come up in English fairly frequently. For example "oct-" means 8 carbons long (think octopus).

1 carbon = meth-

2 carbons = eth- 

3 carbons = prop- 

4 carbons = but-

5 carbons = pent- (like pentagon)

6 carbons = hex- (like hexagon)

7 carbons = hept- *

8 carbons = oct- (like octagon, octopus)*

9 carbons = non- *

10 carbons = dec- (like decimal)*

*Historical note: before January and February were added to the Roman calendar there were only ten months, starting with March. This made September (sept-, hept-) the seventh month, October (oct-) the eighth month, November (no-, non-) the ninth month, and December (dec-) the tenth month. 

The suffix of the name determine what types of bonds are between the carbon atoms. These are "-ane" meaning single bonds, "-ene" meaning double bonds, and "-yne" meaning triple bonds. The placement of the double and single bonds is indicated with the number of the first carbon it's attached to (e.g. 3-octene means a double bond between the third and fourth carbons).

So a molecule that is ten carbons long ("dec-" ...think decimal) with only single bonds (-ane) would be decane. If instead of all single bonds that molecule had a double bond between the second and third carbons it would be 2-decene.

But not all molecules are straight lines of carbons. Sometimes they have pieces (a.k.a. substituents) branching off of them. These branches are similarly named (if they are composed of a carbon chain) by combining the prefixes above with the suffix "-yl" (indicating it's a branch from the main chain). If the branch is not a carbon, then the beginning of the name of the atom is used (for example a chlorine atom would add the prefix "chloro-") .The branch name is then followed by the main chain's name. 

So, if at the fourth carbon (4-) there is a branch with a single carbon (meth-) attached (-yl) to the main chain (2-decene) it would be 4-methyl-2-decene, while having a bromine instead in the same location would be called 4-bromo-2-decene.

Some non-linear carbon chains are actually rings. This adds the prefix cyclo- (think bicycle, meaning two wheels) in front of the number of carbons in the ring. Cyclopentane, then, is a ring of singly-bound carbons. 4-methyl-2-cyclodecene is a ring of ten carbons, with a double bond between the second and third carbon in the ring, and the substituent of a single carbon attached at the fourth carbon in the ring.

There are a number of additional prefixes and suffixes indicating other structural features, such as -ol (indicating alcohol) and -anoic acid (indicating the last carbon in the chain has a double bond to an oxygen and a single bond to another oxygen). 

Hopefully now that you know how chemicals are named, while you may be more comfortable with names like "nail polish remover" than "propanone" you will no longer be surprised to find out that they are exactly the same thing!