Topic 8 Aldehydes and ketones

• Aldehydes and ketones are both carbonyl compounds but the functional group, C=O, is in a different position
• Aldehydes have their carbonyl group at the end of the carbon chain, CHO.
• Where do aldehydes have their functional group? [1]

  End of carbon chain
• How is an aldehyde represented in a structural displayed equation? [1]

  CHO
• Ketones have their carbonyl group in the middle of the carbon chain, CO
• Where do ketones have their carbonyl group? [1]

  Middle of carbon chain
• How are ketones represented by letters? [1]

  CH3COCH3. CO
• What is the product of oxidising an aldehyde? [1]

  Carboxylic acids
• What reagents are used to test for an aldehyde? [2]

  Tollens

  Fellings
• How does Tollens reagent test for an aldehyde but not a ketone? [2]

  Tollens is colourless solution of silver nitrate dissolved in aqueous ammonia

  Aldehydes produce a silver mirror when heated and oxidised

  Ketones produce no visible change
• How does Fehlings solution test for an aldehyde and not a ketone? [2]

  Fehlings is blue as it is copper(II) dissolved in NaOH

  Aldehyde turns from blue to brick red precipitate

  ketones produce no visible change
• For reducing an aldehyde to an alcohol it is a reduction reaction and uses NaBH4 dissolved in water with methanol
• Aldehydes can undergo nucleophillic addition
• How does an aldehyde undergo nucleophillic addition?[2]

  Potassium cyanide KCN used to reduce hydroxynitriles

  nucleophile attacks the molecule and adds itself as an extra group
• Check notes for nucleophillic addition for aldehydes
• Reducing an aldehyde produces a primary alcohol
• Reducing a ketone produces a secondary alcohol
• What does reducing an aldehyde produce? [1]

  Primary alcohol
• What does reducing a ketone produces? [1]

  Secondary alcohol