C16 organic analysis

• the test for alkenes is:

  • add bromine water + shake
  • positive result = colour change from orange-brown to colourless
• the test for halogenoalkanes is:

  • add sodium hydroxide and warm
  • acidify with nitric acid
  • add silver nitrate
  • positive result = precipitate of silver halide forms, white/cream/yellow
• the test for alcohols is:

  • add acidified potassium dichromate
  • positive result is colour change from orange to green
  • positive result could be for primary or secondary alcohols, or aldehydes
• the tests for aldehydes are:

  • warm with fehling's solution
  • positive = colour change from blue to brick-red precipitate
  • or
  • warm with tollens' reagent
  • positive = silver mirror forms
• the test for carboxylic acids is:

  • add sodium hydrogencarbonate
  • bubble gas produced through limewater
  • positive = limewater turns cloudy
• mass spectrometry is an analytical technique used to identify compounds and determine their molecular formula
• high resolution mass spectrometry is a much more sensitive form of mass spectrometry which allows the Mr of a substance to be determined to several decimal places
• mass spectrometry produces a graph called a mass spectrum
• a mass spectrum often contains many more lines than there are elements, despite each line representing one m/z, because the molecular ion formed from ionisation can split up into further fragments, each of which forms a peak on the mass spectrum
• infrared spectroscopy is an analytical technique which uses infrared radiation to determine the functional groups present in organic compounds
• in infrared spectroscopy, the infrared radiation is passed through the sample, where the different types of bonds absorb different amounts of it, the varying amounts of absorbance are measured and recorded, allwing specific bonds and functional groups to be identified
• infrared spectroscopy produces a graph called an infrared spectrum
• different bonds and functional groups have characteristic curves which appear on an infrared spectrum so can be used to identify them
• to identify a compound from an infrared spectrum, use the data sheet to match wavenumber values to the peaks on the spectrum
• on an infrared spectrum:

  the -OH alcohol group is deeper, more curved, and separate from the peaks to the right

  the -OH acid group is shallower, less curved, and merged with the peaks to the right
• the fingerprint region is the area of an infrared spectrum below about 1500cm^-1, it is unique to that substance, so can be used to identify it