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Isomerism Index

Molecules Index


Creative Chemistry Molecular Models

Functional Isomerism

What is it?

Functional isomerism, an example of structural isomerism, occurs substances have the same molecular formula but different functional groups. This means that functional isomers belong to different homologous series. You wont meet these in GCSE Chemistry, but you do come across them at AS/A Level. There are two functional group isomers of which you need to be aware:

  • alcohols and ethers
  • aldehydes and ketones

What is here?

I have put models of the functional isomers ethanol and methoxymethane, and propanal and propanone here. These are typical of the sort of molecules you meet at AS/A Level. You should be prepared to spot functional isomers for simple organic compounds like these for your examinations, and you also need to be able to name the them.






Alcohols have the hydroxyl group,
OH. Ethers have the functional group ROR'.



propanone (acetone)




Aldehydes and ketones both have the carbonyl group C=O. In ketones this is attached to two carbon atoms; in aldehydes it is attached to 1 or 2 hydrogen atoms.

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The models are shown as labelled wireframes to begin with. Right click to get a menu of options, such as animations and changing to space-filling models. You can also move the models using the left mouse button.

Molecular modelling applet courtesy of ChemAxon Ltd


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