Organic Nomenclature

The key to working out what molecule you have is being able to name it. To do this IUPAC (the International Union of Pure and Applied Chemistry) have a few rules which you can follow to name any organic molecule

Here is a quick guide

  1. Identify the functional groups (Alkane, alkene, carboxylic acid, alcohol etc)
  2. Find the longest chain of carbons which include the functional group
  3. Identify any substituents (groups not on the chain)
    These go in alphabetical order with their numerical position directly before them.
  4. Find the direction of numbering the chain that gives the lowest sum for the substituents
    (certain functional groups define the start of a chain. For example – Carboxylic acids, aldehydes, esters, amides etc)
  5. There are no spaces between the parts of the name (except for carboxylic acids). Numbers are separated by commas from each other and by hyphens from letters

Example 1

nomenclature

Using the rules:

  1. alcohol group – all else alkane
  2. 6 carbons in longest chain
  3. 1 methyl group
    1 alcohol group
  4. Numbering from right gives
    1 methyl group on 2nd carbon
    1 alcohol group on 3rd carbon

Gives us the name
2–methylhexan–3-ol

Example 2

nomenclature 2Using the rules:

  1. Carboxylic acid group (Denotes numbering start point)
    all else alkane
  2. 8 carbons in longest chain
  3. 1 ethyl group
    1 methyl group
  4. Numbering from left as it’s a carboxylic acid

Gives
6–ethyl-5–methyloctanoic acid