Organic Analysis

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    • If the mass spectrum is examined under high resolution, the complete molecular formula can be reduced.
    • High resolution mass spectrometry measures the Mr to 4 d.p
    • Different frequencies of infra-red radiation cause different bonds within an organic molecule to vibrate.
    • An infra-red spectrum is obtained by passing a range of infra-red frequencies through a compound, producing absorption peaks. Matching these peaks to those of known bonds help us to identify structural features in an unknown compound.
    • The fingerprint region of an IR spectrum is the region bellow 1500cm-1
    • The absorbencies in this region are unique for any particular chemical, so any molecule can be identified when comparing to a database.
    • Acidified potassium dichromate (K2Cr2O7) can be used to distinguish between primary, secondary and tertiary alcohols.
    • Acidified potassium dichromate oxidises primary and secondary but not tertiary alcohols. The colour change is from orange to green.
    • Use fractional distillation to collect the products of oxidation. Then test this product to see if an aldehyde or ketone is formed.
    • If aldehyde is formed, initial alcohol was primary.
      If ketone is formed, initial alcohol was secondary.
    • Fehling's solution oxidises aldehydes but not ketones. Colour change from blue to brick red precipitate.
    • Test for alkenes by reacting with bromine water. Shake together. Colour change from orange to colourless. Bromine water reacts with the double bond to form a dibromoalkane.
    • Test for carboxylic acid by reacting with a carbonate. Bubble the gas produced through limewater and it turns cloudy.
    • IR Spectroscopy uses infrared radiation to increase the vibrational energy of covalent bonds in a sample.
    • Greenhouse gases in the atmosphere absorb infrared radiation.
    • Electromagnetic radiation from the sun reaches the Earth and is absorbed by the land and sea. Some of this radiation is re-emitted as infrared.
    • The covalent bonds within greenhouse gases absorb infrared radiation and re-emit this back towards the Earth.
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