Lesson 3, Topic 1
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Naming organic molecules rules (nomenclature)

We will use this molecule as an example


  • Count the longest chain of carbon atoms to get the stem of the molecule name
  • If there are two carbon chains of the same length , the main carbon chain will be the one with the most side chains attached.
  • You include the carbon in a functional group when counting the chain length if there is one
  • In this case the stem will be pent



The functional groups gives you the Prefix and/or suffix. In this case the molecule is an alcohol so will end in the suffix  – ol



  • Number the longest carbon chain so that the lowest number carbon has the main functional group.  
  • Where there is a halogen and another functional group the halogen is counted second

Pentan - 2 - ol


Use di, tri and tetra to indicate the number of identical side branches. If different side branches are present they are listed alphabetically 

3 ethyl - 2,4 di methyl pentan -2- ol