Analysis

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  • Created by: Anon
  • Created on: 24-02-15 15:34
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  • Analysis
    • Chromatography
      • Paper chromatography
        • The stationary phase is the paper
        • The mobile phase is the solvent
        • Separation of the compounds is by adsorption to the paper
        • The chromatogram produced can be quantified with an Rf value
        • An Rf value gives the ratio of the distance migrated by the compound, compared with the solvent front
        • Rf value= Distance traveled by compound/ distance of solvent front
        • You can then identify the compound by comparing it to a database of known Rf values
      • Gas chromatography
        • The stationary phase is the liquid coating the tube
        • The mobile phase is the gas pushing the compounds along the tube
        • Compounds are separated by solubility to the stationary phase
        • A gas chromatogram can be quantified by retention time
        • Retention time= The time between the compound entering and leaving the column
        • High temperatures are required so the technique is unsuitable for biological molecules such as enzymes
        • Similar compounds may have similar retention times and so cannot be easily separated
    • Mass spectroscopy
      • Gas chromatography can be combined with mass spec. GC separates the compounds, MS identifies them
      • All species on a mass spectrum have a 1+ charge
      • Molecular ion peak= the peak furthest to the right on the spectrum, with the highest m/e value. This gives the Mr of the compound
      • Fragment ions= the bits that the molecule will split into, you will be able to find the Mr of these ions using the m/e value
      • You may encounter a spectrum that seems to have a missing molecular ion peak, this is because the compound has been fragmented so much that the molecular ion peak is no longer significant
    • NMR
      • Splitting scenarios
        • 1.Protons on an adjacent carbon to one side only- the signal will be split very simply using the n+1 rule
        • 2. Equivalent protons- for example ethane has 6 protons all in the same environment, they are described as equivalent and so do not split
        • 3. Protons on adjacent carbons to both sides, when the protons are of the same type- for example propane. The two protons in the middle will be equally split by the 6 protons around them using the n+1 rule into a septet
        • 4. Protons on adjacent carbons to both sides, when the protons are of different types- this causes messy splitting and is called a multiplet
        • 5. OH, NH and SH groups do not experience or cause splitting
      • NMR rules
        • Proton NMR gives more structural information than carbon 13 NMR and so is more useful
        • The line of integration on each peak gives the ration of protons in that environment
        • The amount of signal splitting is determined by n + 1. Where n= the number of protons on the adjacent carbon
        • The NMR machine must be calibrated using TMS (tetramethylsilane) before each use
        • The solvent used in NMR is CDCl3 because it does not give any peaks on the spectrum
        • OH peaks can be identified using D2O. When the spectrum is run with D2O the OH peak will disappear

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