Nucleophilic addition

• Reduction of aldehydes and ketones with NaBH4to form alcohols

  NaBH4 is sodium borohydride

  • It's mechanism is nucleophilic addition with the nucleophile being H- (hydride ion)
  • In acidic conditions
  • E.g. CH3CH2CHO + 2 [H] --> CH3CH2CH2OH which is proponal --> propan-1-ol
  • [H] is the reducing agent
• Optical isomers react acidified hydrogen cyanide

  They form a racemic mixture and the mechanism involved is nucleophilic addition e.g. Ethanal reacting with HCN

  • The CN has a negative charge and a pair of electrons that goes to the carbon with the double bonded oxygen
  • One bond from the double bonded oxygen goes to the oxygen to make it negative
  • The pair of electrons from oxygen goes to the hydrogen
  • And it forms 2-hydroxypropanenitrile
• Both aldehyde and ketones go through nucleophilic addition to form hydroxynitriles

  Conditions required:

  • KCN as a reagent
  • HCl which provides the H+ ions
  • Under reflux
• Phenylketones go through nucleophilic addition to form phenylalcohol

  Conditions required:

  • Reagent is NaBH4
  • Nucleophile is H- ion
  • In aqueous solutions
• Phenylketones go through nucleophilic addition to form phenylhydroxynitrile

  Conditions required:

  • Reagent is KCN
  • In reflux