3.8 Aldehydes and Ketones

• What is a carbonyl group?

  C=O
• What is the functional group of an aldehyde?

  H-C=O
• What is the functional group of a ketone?

  RC=OR
• How do you name an aldehyde?

  Using the suffix -anal
• How do you name a ketone?

  Using the suffix -one
• What can aldehydes be oxidised to?

  Carboxylic acids
• What oxidising agent do you use?

  Acidified potassium dichromate (K2Cr2O7)
• What chemical tests can you use to distinguish between aldehydes and ketones?

  Fehling's solution

  - aldehyde is oxidised to a Carboxylic acid and the Cu 2+ ions are reduced to Cu+

  - blue to brick red precipitate

  
  

  Tollen's Reagent

  - aldehyde is oxidised to a Carboxylic acid and silver is reduced to metallic silver

  - silver mirror produced
• What reducing agent is used to reduce aldehydes and ketones?

  NaBH4 (aq)
• What mechanism is used to reduce an aldehyde/ketone?

  Nucleophilic Addition
• Why is an aldehyde/ketone reduced but not an alkene?

  Nucleophile is repelled by the high electron density in the C=C bond but is attracted to the C(delta positive) in the C=O
• What reagents are needed to form a hydroxynitrile?

  KCN and H2SO4
• Why is KCN used instead of HCN?

  HCN is a very toxic gas that is highly flammable where as KCN is a solid so whilst its still toxic it is safer to store
• Give an equation to show the formation of HCN from KCN and H2SO4.

  2KCN(s) + H2SO4(aq) -> 2HCN(g) + K2SO4(aq)
• What molecules produce a molecule with a chiral centre in the formation of a hydroxynitrile?

  All aldehydes and unsymmetrical ketones
• What kind of optical isomer is produced?

  A racemate because the carbonyl group is planar so there is an equal chance that the nucleophile (:CN-) will attack either side of the molecule
• What is a carbonyl group?

  C=O
• What is the functional group of an aldehyde?

  H-C=O
• What is the functional group of a ketone?

  RC=OR
• How do you name an aldehyde?

  Using the suffix -anal
• How do you name a ketone?

  Using the suffix -one
• What can aldehydes be oxidised to?

  Carboxylic acids
• What oxidising agent do you use?

  Acidified potassium dichromate (K2Cr2O7)
• What chemical tests can you use to distinguish between aldehydes and ketones?

  Fehling's solution

  - aldehyde is oxidised to a Carboxylic acid and the Cu 2+ ions are reduced to Cu+

  - blue to brick red precipitate

  
  

  Tollen's Reagent

  - aldehyde is oxidised to a Carboxylic acid and silver is reduced to metallic silver

  - silver mirror produced
• What reducing agent is used to reduce aldehydes and ketones?

  NaBH4 (aq)
• What mechanism is used to reduce an aldehyde/ketone?

  Nucleophilic Addition
• Why is an aldehyde/ketone reduced but not an alkene?

  Nucleophile is repelled by the high electron density in the C=C bond but is attracted to the C(delta positive) in the C=O
• What reagents are needed to form a hydroxynitrile?

  KCN and H2SO4
• Why is KCN used instead of HCN?

  HCN is a very toxic gas that is highly flammable where as KCN is a solid so whilst its still toxic it is safer to store
• Give an equation to show the formation of HCN from KCN and H2SO4.

  2KCN(s) + H2SO4(aq) -> 2HCN(g) + K2SO4(aq)
• What molecules produce a molecule with a chiral centre in the formation of a hydroxynitrile?

  All aldehydes and unsymmetrical ketones
• What kind of optical isomer is produced?

  A racemate because the carbonyl group is planar so there is an equal chance that the nucleophile (:CN-) will attack either side of the molecule