• Question: How do you identify different types of molecules?

    Asked by anon-358140 on 29 Mar 2023.
    • Photo: Graeme Dykes

      Graeme Dykes answered on 29 Mar 2023:


      There are usually a set of techniques which you can combine to identify a molecule. You might start with LCMS. This checks for how many different molecules are present, in what proportions and what are their masses.
      If you can get a nice crystal (which is often hard to do)then you could use x-ray crystallography
      If you have a single molecule, you might use nuclear magnetic resonance to look at what carbon, hydrogen atoms are present. You might also look at infrared spectroscopy to find out how these are arranged.

    • Photo: Martin McCoustra

      Martin McCoustra answered on 29 Mar 2023:


      There are a wide range of ways to identify different types of molecule. All of them rely on the interaction of electromagnetic radiation with the molecules. One of the, NMR, allows us to very accurately work out the structure of molecules by looking at the number and location of carbon and hydrogen atoms. This is the area of chemistry and physics known as spectroscopy.

    • Photo: Rebecca Walker

      Rebecca Walker answered on 29 Mar 2023:


      There are a lot of different analytical techniques you can use to identify what molecule you have made after an organic synthesis. Once a reaction is complete, we will typically use NMR (nuclear magnetic resonance) spectroscopy to confirm we have made what we think we have – this can tell us about the location of certain atoms in the molecule with respect to other atoms, and from this we can build up the pieces of the molecule like a puzzle. Infrared spectroscopy can help us determine if the correct functional groups are present in a molecule (for example, an alcohol will have a characteristic ‘peak’ in an IR spectrum that will not be present after it is oxidised to an aldehyde).

    • Photo: Jade Markham

      Jade Markham answered on 31 Mar 2023:


      We use something called NMR.

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