Organic synthesis

• Samples are dissolved in inert solvents with no 1 Hydrogen atoms, e.g. CCI, CDCl.

  These solvents have no H atoms so will not give any peaks in the 'H NMR spectrum.
• CCl4 is a non-polar compound that is a good solvent for non-polar organic molecules

  CDCl3 is a polar covalent molecule that is a good solvent for polar organic molecules.
• TMS is used because:

  • it only gives one signal
  • its signal is away from all the other H signals
  • gives strong signal so only a small amount needed
  • it is non-toxic
  • it is inert
  • it has a low boiling point and so can be removed from sample easily
• chemical shift

  • relative scale of how far the frequency of the proton signal has shifted away from that for TMS
• State why Si(CHi), CCl4 and CDCl3 are used in 'H NMR spectroscopy.

  • CDCl3 or CCl4 act as a solvent
  • TMS as reference peak at 0 (ppm)
  • inert so unlikely to react with sample
• Explain how their properties make them suitable for use in 1H NMR spectroscopy.

  • CCI4 or CDCI3 as solvent
  • Both have no H atoms so give no signals in spectrum tied to either CDCL3, or CCI4
  • CCl4 is non polar
  • CDCl3 is polar covalent molecule
  • TMS gives one signal
  • signal given in a area away from other typical H signals
• Fractional distillation is not a suitable method to separate the mixture of chlorinated compounds before identification by mass spectrometry. Suggest how the mixture could be separated.

  chromatography GLC TLC
• Suggest one operating condition in an incinerator that would minimise the formation of dioxin

  * Use of excess air/oxygen or high temperature (over 800 oC) or remove chlorine-containing compounds before incineration