6. Organic analysis

• High res mass spec can distinguish between molecules which have only a small difference in their molecular masses
• Infrared spectroscopy is used to identify certain bonds within a compound
• Acidified potassium dichromate can be used to distinguish between primary, secondary and tertiary alcohols
• Acidified potassium dichromate oxidises primary and secondary alcohols but not tertiary
• Because primary and secondary alcohols give the same colour change, we use fractional distillation and then test to see if an aldehyde or ketone is formed
• Fehlings solution is an oxidising agent so oxidises aldehydes but not ketones
• How to make tollens:

  1. Add few drops of sodium hydroxide to silver nitrate solution
  2. Add a few drops of dilute ammonia until ppt dissolves
• Aldehydes and ketones are flammable so we dont use a bunsen burner
• Test for carboxylic acid is adding carbonate

  • CO2 gas and water is made
  • When bubbled through limewater, it turns cloudy
• mass spec is used to find the Mr of a compound
• m/z is the mass of a fragment divided by charge
• Most fragments have a 1+ charge so m/z = fragment mass
• Peaks show fragments of the original compound
• The last peak is the M+ peak or molecular ion peak

  • Its the same as relative molecular mass of the molecule
• High res mass spec measure the relative mass to several decimal places
• IR spectroscopy uses infrared radiation to increase the vibrational energy of covalent bonds in a sample
• The frequency of IR radiation absorbed by a covalent bond depends on:

  1. The atoms that are on either side of the bond
  2. The position of the bond in the molecule
• The fingerprint region allows us to identify specific molecules
• You can compare the fingerprint region against a known library of spectra to identify the molecule
• Extra peaks in the fingerprint region indicates you have impurities in the samle
• Green house gases in the atmosphere absorb infrared radiation and re emit it back towards earth - gh effect

  • it is usually the covalent bonds that absorb the IF radiation
• GHG include:

  CO2

  H2O

  CH4