6.1.7

• • if c=o is on one end carbon, aldehyde formed
  • if c=o is not at the end of carbon chain, ketone
• oxidation

  aldehydes will undergo oxidation to form carboxylic acid

  • the reagents are potassium dichromate, K2Cr2O7 and sulphuric acid H2SO4

  → reagents react in situ to form to form the oxidising species Cr2O7 2-, and H+

  • in the laboratory the reaction mixture is gently heated under reflux,colour change from orange to green,due to the oxidation state of the chromium changing
• Nucleophilic Addition reactions

  C=O has a dipole making them susceptible to nucleophilic attack on electropostive carbon atom

  product → C=O break + reactive intermediate is formed + extra electron is donated to the neighbouring H atom to form an alcohol group + stable product

  modelled in a general mechanism
• Nucleophilic Addition

  Sodium tetrahydridoborate (III)

  NaBH4

  use : made of a BH4 - ion, which acts a source of hydride ions, H-

  → the hydride ion is species involved in electrophilic addition + reduction of carbonyl compounds to alcohol
• Nucleophilic addition

  Hydrogen cyanide

  weak acid that will partially ionise in solution

  • cyanide nucleophile with a negative charge on carbon atom is formed

  HCN + H2O eqm CN- + H3O+

  other sources of CN-

  • CN- cannot react directly with C=O

  → when reaction is acidified, carbonyl functional group becomes more reactive as polarity of C=O bond is increased

  summarised as a mechanism

  • in the second step, the hydrogen could also be obtained from another molecule in the reaction mixture such as ethanol
  • addition of cyanide allows further carbon atoms to be added to the organic molecule