Structural Analysis

  1. Elemental microanalysis (combustion analysis) can be used to determine which elements in a sample of an organic compound in order to find the empirical formula?
    C, H, S and N
  2. What is the empirical formula of a compound?
    The empirical formula is the simplest whole number ratio of the different atoms in a compound
  3. What structural analysis technique is used to determine the molecular mass and structural features of an organic compound?
    Mass spectrometry
  4. How does a conventional mass spectrometer work?
    • The sample is firstly vaporised and then ionised by being bombarded with electrons
    • Fragmentation can occur when the energy available is greater thean the molecular ionisation energy
    • The parent ion and ion fragments are accelerated by an electric field and then deflected by a magnetic field
    • The strength of the magnetic field is varied to enable the ions of all the different mass / charge ratios to be detected in turn.  A mass spectrum is obtained.
  5. What is the name of the ion which gives the highest peak on a mass spectrum?
    The molecular ion / parent ion
  6. What is infra-red spectroscopy used for?
    To identify certain functional groups in an organic compound
  7. How does infra-red spectroscopy work?
    Infra-red radiation causes parts of a molecule to vibrate.  The wavelengths which are absorbed and cause the vibrations will depend on the type of chemical bond and the groups or atoms at the ends of these bonds.
  8. How do you work out wavenumber? And what are it's units?
    • Wavenumber = 1 / wavelegnth = 1 / λ
    • Units are cm-1
  9. What does Nuclear Magnetic resonance spectroscopy (nmr) give information about?
    • The different environments of hydrogen atoms in an organic molecule
    • How many hydrogen atoms there are in each environment
  10. In nmr what is the function of TMS?
    It is a standard reference substance (which is assigned a chemical shift equal to 0)
  11. What is X-ray crystallography used for?
    To determine the precise three dimensional structure of organic compounds
  12. Which element has a low electron density and is not easily detected by X-rays?
  13. How X-ray crystallography work?
    A crystal of an organic compound acts as a diffraction grating when it is exposed to X-rays of a single wavelength the atoms of the crystal act as a diffraction grating
  14. What kind of maps are produced from X-ray crystallography?
    Electron-density maps
Card Set
Structural Analysis
Advanced Higher Chemistry - Unit Three - Structural Analysis