Naming alcohols and ethers

Alcohols and general nomenclature guidelines  
stem name carbon number
meth 1
eth 2
prop 3
but 4
pent 5
hex 6
 

4-methylpentan-2-ol
 
  • Names for organic compounds have three parts: prefix(es), stem, and ending

    Locators (numbers) are given before the prefix and the ending to show the position of groups on the longest chain if they are required to clarify the position of the group(s) on the chain. 
     
  • The ending for alcohols is -ol 
     
  • The stem used depends on the number of carbons in the longest chain containing the carbon bearing the OH.

    In the alcohol at the right, the longest chain including the carbon bearing OH has five carbon atoms.
     
  • Substituents on the longest chain are included in the name as prefixes.
    Any atom or group of atoms replacing H at a carbon is called a substituent.
     
    chloro Cl– methyl CH3– Note: Saturated hydrocarbon substituents have the same name as the parent alkane except with -ane substituted by -yl.
    bromo Br– ethyl CH3CH2–

  • The functional group determines the numbering of the chain.
     
    In an alcohol, the carbon bearing OH has the lowest possible number.
    Carbon 1 can be at either end of the chain.  In the example above carbon 1 is at the right-hand side.
    If the OH had been at a different position, carbon 1 may have been on the left-hand side.

Ethers
 
  • Ethers are named as substituted alkanes.  Thus the ending is -ane.  Examples of the substituent names are given below.

    methoxy CH3O– 
    ethoxy CH3CH2O–
     
  • The position of the oxy substituent determines the numbering of the chain.
Dr Sheila Woodgate
© The University of Auckland 2002