Alkane Nomenclature

In chemistry, every single molecule needs a unique name. We can’t have two molecules with the same name or that would get super confusing! For this, we use IUPAC nomenclature. 

Alkane Nomenclature Overview

Basically there are 4 different parts to naming most molecules:

  • The Root or Parent Chain (this tells us about overall chain length)
  • Modifiers (tells us what functional groups are attached to the chain)
  • Substituents (tells us about what is branching off that chain)
  • Numerical Locations (tells us where those branches are)

Alkane Prefixes

Memorizing sucks, I get it. But unfortunately this is something you’re just gonna have to remember. Not all professors will make you memorize all 12- check with your professor to figure out how many you need to know!

IUPAC Alkane Naming Rule #1

Remember, if there is a TIE between two chains of equal length, go with the chain that gives the MOST substituents!

IUPAC Alkane Naming Rule #2

Now we know the length of the root chain, but nothing else! We need to determine which carbon gets the “1” location. 

  • Start numbering the root chain starting from the closest substituent
    • If there is a tie between locations, compare the locations of the next substituents
    • If there is STILL a tie between ALL locations, decide using alphabetical order.

The key here is to get the lowest numbers possible for ALL of your locations (at least for now). Now give it a shot by yourself!

Example: Name the longest carbon chain and determine the direction of the root chain 

3m

If you got this one wrong, don’t worry too much. You’ve got plenty more chances to nail this. 

IUPAC Alkane Naming Rule #3

So we know the length and direction of the root chain, which is great. But if there are ANY branches on this chain, we need to name those too.

P.S. The term “substituent” is just a nerdy word for a “branch”. 

NOTE: Alkane substituents require a “-yl” suffix to indicate that they are a branch! (i.e. ethane becomes ethyl). 

Sick job! We’re getting closer to fully naming these guys. 

IUPAC Alkane Naming Rule #4 and #5

Now we have all the pieces we need to name most alkanes, but we need to work on our formatting! Chemists are surprisingly analytical making sure all your commas and numbers are in the right place.

In short:

  • Always name your substituents in alphabetical order
  • Commas separate numbers from numbers, and dashes separate numbers from letters (i.e. 1,2-dimethyl)

Example: Provide the IUPAC name for the following alkane

8m

Does this make sense? You just learned how to name simple alkanes. Give yourself a pat on the back!