aldehydes & ketones

• Carbonyls


  Compounds with a C=O bond
• Types of carbonyls

  • Aldehydes
  • Ketones
• Aldehyde

  C=O is on the end of the chain with an H attached
• Ketone


  C=O is in the middle of the chain
• Solubility of smaller carbonyls in water

  They can form hydrogen bonds with water
• Intermolecular forces in carbonyls

  • Pure carbonyls cannot hydrogen bond to themselves, but are attracted instead by permanent dipole forces
• C=O bond in carbonyls

  • It is stronger and does not undergo addition reactions easily
  • It is polarised because O is more electronegative than carbon, attracting nucleophiles
• Oxidation of alcohols


  • Primary alcohols are oxidised to aldehydes, then to carboxylic acids
  • Secondary alcohols are oxidised to ketones
  • Tertiary alcohols do not oxidise
• Oxidation of aldehydes


  1. Aldehyde + [O] → Carboxylic acid

  2. Reagent: Potassium dichromate (VI) solution and dilute sulfuric acid

  3. Conditions: Heat under reflux
• Observation: The orange dichromate ion (Cr2O7^2-) reduces to the green Cr^3+ ion during the oxidation of aldehydes
• Aldehydes can also be oxidised using Fehling's solution or Tollen's reagent, which are used as tests for the presence of aldehyde groups
• Reduction of carbonyls


  1. Reducing agents like NaBH4 or LiAlH4 will reduce carbonyls to alcohols

  2. Aldehydes are reduced to primary alcohols

  3. Ketones are reduced to secondary alcohols
• Catalytic hydrogenation of carbonyls

  1. Reagent: Hydrogen and nickel catalyst

  2. Conditions: High pressure
• When naming hydroxynitriles, the CN becomes part of the main chain and carbon no 1
• Nucleophilic addition of HCN to aldehydes and unsymmetrical ketones results in the formation of a racemate, with no optical activity observed