Aldehydes and Ketones

• What is the general formula for aldehydes and ketones?

  CnH2nO
• Aldehydes and ketones both contain the carbonyl group, which is written as C=O
• Aldehydes and ketones with the same number of carbon atoms are functional group isomers.
• Give an example of functional group isomers with the molecular formula C4H8O.

  Butanal and butanone
• Chain isomers of pentanal include 2-methylbutanal, which has a branched chain
• Steps for preparing aldehydes and ketones by oxidation of alcohols

  1️⃣ Oxidize the alcohol

  2️⃣ Use acidified potassium dichromate

  3️⃣ Observe the color change from orange to green
• What is the product when aldehydes are oxidized?

  Carboxylic acids
• Warming an aldehyde with Tollens' reagent produces a silver mirror
• Ketones can be further oxidized using Tollens' reagent or Fehling's solution.

  False
• What complex ion is present in Tollens' reagent?

  [Ag(NH3)2]+
• Fehling's solution contains Cu²+ ions, which are reduced to Copper(I) oxide, CuO
• Aldehydes and ketones contain a polar C=O bond that makes them susceptible to nucleophilic attack.
• What is the definition of a nucleophile?

  Electron pair donor
• Aldehydes and ketones can be reduced to alcohols using NaBH4 in aqueous solution
• Aldehydes are reduced to form primary alcohols, while ketones form secondary alcohols.
• Match the aldehyde or ketone with its reduction product:

  CH3CH₂CHO ↔️ CH3CH₂CH₂OH

  CH3COCH₂CH3 ↔️ CH3CHOHCH₂CH3

  Cyclohexanone ↔️ Cyclopentanol
• What type of mechanism is involved in the reduction of aldehydes and ketones?

  Nucleophilic addition
• Outline the mechanism for the reduction of ethanal with NaBH4

  1️⃣ Lone pair on hydride ion attacks 8+ carbon

  2️⃣ New covalent bond forms with carbon

  3️⃣ Protonation of oxygen by water

  4️⃣ Ethanol is formed
• Aldehydes and ketones can be converted to hydroxynitriles by the addition of HCN
• Reacting an aldehyde or ketone with cyanide increases the length of the carbon chain.
• Match the aldehyde or ketone with its hydroxynitrile product:

  CH3CH₂CHO ↔️ 2-hydroxybutanenitrile

  CH3CH₂COCH₂CH3 ↔️ 2-ethyl-2-hydroxybutanenitrile
• Outline the mechanism for the reaction of ethanal with KCN followed by dilute HCl

  1️⃣ CN- nucleophile attacks 8+ carbon

  2️⃣ New covalent bond forms with carbon

  3️⃣ Protonation of oxygen by HCl

  4️⃣ 2-hydroxypropanenitrile is formed
• Why is KCN preferred over HCN as a reagent in nucleophilic addition reactions?

  HCN is a toxic gas
• When unsymmetrical ketones react with KCN followed by dilute acid, a racemic mixture of two enantiomers is formed.
• Optical isomers are non-superimposable mirror images.
• What is the shape around the C=O bond in aldehydes and ketones?

  Trigonal planar
• In nucleophilic addition reactions, attack from either side of the trigonal planar C=O bond is equally likely.
• Outline the mechanism for the reaction of pentan-2-one with KCN followed by dilute HCl

  1️⃣ CN- nucleophile attacks 8+ carbon

  2️⃣ New covalent bond forms with carbon

  3️⃣ Protonation of oxygen by HCl

  4️⃣ Optical isomers of product are formed
• Match the reaction type with its reagent:

  Oxidation of aldehydes ↔️ Acidified potassium dichromate

  Reduction of aldehydes and ketones ↔️ NaBH4

  Addition of HCN ↔️ KCN followed by dilute acid