carbonyls

• 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
• Pure carbonyls cannot hydrogen bond, but bond 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, so the positive carbon atom attracts nucleophiles
• Oxidation of alcohols


  • Primary alcohol aldehyde carboxylic acid
  • Secondary alcohol ketone
  • Tertiary alcohols do not oxidise
• Oxidation of aldehydes


  1. Reagent: potassium dichromate (VI) solution and dilute sulfuric acid

  2. Conditions: heat under reflux

  3. Reaction: RCHO + [O] RCO2H
• Oxidation of aldehydes using Tollens' reagent


  1. Reagent: Tollens' reagent formed by mixing aqueous ammonia and silver nitrate

  2. Conditions: heat gently

  3. Reaction: CH3CHO + 2Ag+ + H2O CH3COOH + 2Ag + 2H+
• Observation: with aldehydes, a silver mirror forms coating the inside of the test tube. Ketones result in no change.
• Reduction of carbonyls


  1. Reagents: NaBH4 or LiAlH4

  2. Conditions: Room temperature and pressure

  3. Aldehydes reduced to primary alcohols

  4. Ketones reduced to secondary alcohols
• Catalytic hydrogenation of carbonyls

  1. Reagent: hydrogen and nickel catalyst

  2. Conditions: high pressure
• Addition of hydrogen cyanide to carbonyls

  1. Reagent: sodium cyanide (NaCN) and dilute sulfuric acid

  2. Conditions: Room temperature and pressure

  3. Mechanism: nucleophilic addition
• The melting point of the crystal formed from the reaction with 2,4-dinitrophenylhydrazine can be used to help identify which carbonyl was used
• 2,4-dinitrophenylhydrazine reacts with both aldehydes and ketones to form an orange precipitate, which can be used as a test for a carbonyl group