module 6 organic

• carbonyl functional group includes aldehydes and ketones that both contain a C=O bond
• in aldehydes the carbonyl is found at the end of the chain, and is written as CHO, methanal :

  
• methanal = formaldehyde, used in solution to preserve biological specimens
• in ketones the carbonyl functional group is joined to 2 carbon atoms in the carbon chain, written as COe
• in ketones, carbonyl group is joined to 2 carbon atoms, ketone group is written as CO
• simplest keton is propanone, CH3COCH3, also known as acetone, used as an important industrial solvent and nail polish removers

  
• reactivity of aldehydes and ketones is influenced by the nature of the carbon-oxygen double bond, which is made up of both a sigma bond and a pi bond

  
• C=C in alkenes is non polar
• C=O in carbonyl compounds is polar
• oxygen is more electronegative than carbon so the electron density lies closer to it than to the carbon, making the C more positive and the O more negative, so aldehydes and ketones react with some nucleophiles
• nucleophile is attracted to and attacks the slightly positive carbon resulting in addition across the C=O double bond
• carbonyl groups undergo nucleophillic additions
• alkenes with the non polar C=C bond react with electrophiles and undergo electrophillic addition
• aldehydes are reduced to primary alcohols by NaBH4, e.g butanal is reduced to butan-1-ol

  
• ketones are reduced to secondary alcohols by NaBH4, e.g propanone is reduced to propan-2-ol

  
• sodium tetrahydridoborate (III) is used as a reducing agent to reduce aldehydes and ketones to alcohols, the aldehyde or ketone is warmed with the NaBH4 in aqueous solution
• carbon atom in the C=O is electron deficient and attracts nucleophiles, aldehydes and ketones both react by nucleophillic addition to form alcohols
• nucleophile


  electron donor, negative ion attacking a carbon e.g cyanide = CN-
• electrophile


  electron pair acceptor, positive ion attacking a carbon e.g NO2+
• chromatography is used to separate mixtures

  • drugs
  • plastic
  • flavourings
  • food
  • pesticides
  • forensic evidence
• pencil used instead of pen in chromatography because it is insoluble so it will not smudge and run which can ruin the experiment
• in chromatography, the solvent must be able to dissolve the sample but not completely dissolve
• in chromatography non aqueous solvents such as ethanol and chloroform are used for less polar samples
• Rf value = component distance travelled / solvent distance travelled
• Rf value always less than 1
• stationary phase in chromatography

  the plate, solid silica (SiO2) supported on glass or plastic sheets
• mobile phase in chromatography

  solvent moves up the TLC plate with silica
• chemicals with a low affinity for silica (non polar compounds) will not want to bond with it so will move quickly up the plate
• chemicals with a high affinity for silica (polar compounds) will form strong intermolecular bonds with silica so will move slowly up the plate and will travel slower
• solid separation


  the more the sample is able to be absorbed onto the stationary phase the slower they move

  
• disadvantages of Rf value

  • similar compounds have similar Rf values
  • if a substance is completely unknown there isn't any value to compare it with
  • difficult to find a solvent that separates the mixture
  • if components are too soluble in the solvent they will be washed
  • if components are not soluble enough the won't move enough
• spectroscopy

  • gas chromatography
  • infrared spectroscopy
  • mass spectroscopy
  • nuclear magnetic resonance
• mass spectrometry

  technique used to identify molecular mass
• mass spectrometry method

  • sample turned into a gas and injected into a high vacuum
  • single stream of molecules allowed to pass into the chamber
  • high energy electrons are fired at the molecules
  • form positive ions
  • fragment is accelerated by an electric field
  • fragment is deflected by a magnetic field
  • lighter particles are deflected more
  • fragments are then detected
• fragmentation

  when molecules are in a mass spectrometer, they can fragment into smaller parts and these fragments are also detected
• isotopes

  ions with different isotopes produce different signals, most important for Br and Cl
• NMR

  technique used to find the structure of molecules, method uses magnetic fields and radio waves, used for:

  • H1
  • C13
  • F19
  • P31

  these are all isotopes
• protons and neutrons have a property called spin
• when a strong magnetic field is applied, all of the nuclei in a substance will align themselves to the field due to their spin, this is the lowest, energy state
• excitation in NMR

  if you apply radio waves to the sample, the nuclei will flip to the higher energy state