organic analysis

• What is the chemical name for the compound with the formula propanoic acid?


  Propanoic acid
• What are the tests for functional groups in organic chemistry?


  • Alkenes: Bromine water (orange to colourless)
  • Primary alcohol: Acidified potassium dichromate (orange to green)
  • Aldehydes: Tollen's reagent (silver mirror), Fehling's reagent (brick red precipitate)
  • Carboxylic acid: Acidified potassium dichromate (orange to green), add carbonate (effervescence)
  • Halogenoalkanes: Acidified silver nitrate (precipitate colors based on halogen)
• What is the result of adding bromine water to alkenes?


  Orange to colourless
• What happens when primary alcohol is treated with acidified potassium dichromate and warmed?


  It changes from orange to green
• What is the result of warming aldehydes with Tollen's reagent?


  It forms a silver mirror precipitate
• What is the result of warming aldehydes with Fehling's reagent?


  It produces a brick red precipitate
• What is the result of adding acidified potassium dichromate to carboxylic acid while heating?


  It changes from orange to green
• What is observed when a carbonate is added to a carboxylic acid?


  Effervescence occurs
• What are the results of adding acidified silver nitrate to halogenoalkanes?


  • C-F: No precipitate (AgF)
  • C-Cl: White precipitate (AgCl)
  • C-Br: Cream precipitate (AgBr)
  • C-I: Yellow precipitate (AgI)
• What happens when dilute ammonia is added to the precipitate formed from halogenoalkanes?


  Chloride dissolves, bromide does not dissolve, iodide does not dissolve
• What happens when concentrated ammonia is added to the precipitate formed from halogenoalkanes?


  Chloride dissolves, bromide dissolves, iodide does not dissolve
• What is the significance of using nitric acid in the test for halogenoalkanes?


  • It acidifies the solution
  • Ensures accurate precipitation of halides
• electrospray ionisation

  MH+ sample gains proton

  pass liquid through a high voltage fine needle which gives a fine spray with a charge
• electron bombardment

  M+ sample looses e-

  high energy electrons collide with the sample
• mass spec

  ion peak is the heaviest mass (m/z)

  cant distinguish between compounds with same molecular formula as they have the same mr

  compounds with Cl or Br will have more than one peak due to isotopes (n+1 rule) (no of Cl or Br atoms add one)
• ir spec

  light is electromagnetic radiation

  it consists of electric and magnetic fields vibrating at the same frequency

  IR vibrates bonds

  all bonds vibrate at a specific frequency, the frequency depends on the mass of the atom, bond strength and type of vibration

  above 1500cm-1 is used to identify functional groups, anything below is the fingerprint region

  O-H (alcohol) has a rounder peak than acid
• NMR

  the absorption of electromagnetic radiation by a nucleus having a magnetic moment when in an external magnetic field, used mainly as an analytical technique and in diagnostic body imaging

  electrons spin in opposite directions relative to the magnetic field so they dont repel each other
• C-13 NMR- how does it work?

  1% of all c isotopes

  acts as a magnet

  the nuclei line up with magnetic field, like electrons (c-12 cant)

  c13 nucleus aligned opposite to magnetic field= higher energy, and other c-13 lined in line with magnetic field= lower energy

  this creates a difference in energy

  unstable to now stable= energy release
• c-13 nmr

  the frequency needed to cause the carbon nuclei to resonate depends on the electron density surrounding it

  environment= bonds carbon makes

  tetramethylsilane = 0PPM is the standard, it resonates evenly as it only has one carbon environment (4 ch3 groups around si) you subtract this peak at zero from ur total number of peaks
• H NMR- how does it work

  H1 acts similarly to c13 in that they line with the magnetic field and will "flip" in radio wavelengths causing resonance

  H1NMR is more abundant so its easier to get a spectrum compared to c13nmr

  the greater the electron density around the h atom, the smaller the chemical shift, due to shielding from electrons

  h nuclei have magnetic spin, so absorb energy from a higher frequency to move to a higher energy state

  the NMR occurs as protons resonate between their spin energy states
• spin spin coupling in H NMR

  H atoms couple together, splitting signals

  lines= number of H next door+1 (n+1)

  intergration ratio is the amount of hydrogen atoms on each carbon atom

  H atoms dont couple to equivalent hydrogens of oxygen or nitrogen atoms