Carbonyl compounds

• What is the carbonyl group?

  C=O
• What is the functional group and general formula for an aldehyde?

  RCHO (C double bonded to O, single bond to H and R)
• What is the functional group for a ketone?

  RCOR' (C double bonded to O)
• How do you name aldehydes?

  • al suffix (C=O is on the end of a chain)
• How do you name ketones?

  • one suffix (designate number for which carbon C=O is on)
• What kind of intermolecular forces do molecules with the carbonyl group have? Why?

  Permanent dipole-dipole due to the polar C=O bond (O is ∂-)
• Which bond in carbonyl compounds is usually involved in reactions? Why?

  C=O, due to the polarity of the bond (large difference in electronegativity between C and O)
• How soluble are carbonyl compounds in water? What influences solubility?

  Yes - form hydrogen bonds with water; solubility decreases as C chain length increases.
• What is the strongest bond in carbonyl compounds?

  C=O
• What is the mechanism for the nucleophilic addition of a carbonyl compound?

  • Nucleophile (:Nu-) attacks the carbonyl carbon
  • Forms a tetrahedral intermediate
  • Protonation leads to the final product

  
• What is the mechanism for the nucleophilic addition of HCN to a carbonyl compound?

  • HCN acts as a nucleophile
  • Attacks the carbonyl carbon
  • Forms a hydroxynitrile

  
• Why is the addition of HCN important?

  It increases the length of the carbon chain by one carbon atom allowing more useful molecules to be made.
• Will the product of HCN added to a carbonyl compound have optical isomers? Why?

  Yes, they will; the carbonyl carbon is planar, allowing attack from either side, forming two enantiomers.
• What is the name of the product when HCN is added to a carbonyl compound?

  Hydroxynitriles (have OH and CN groups)
• What is Fehling’s solution and what colour is it?

  Copper complex ions, blue
• What happens when an aldehyde is added to Fehling’s solution?

  Reduced to Cu+ ions → colour change to brick red ppt
• What happens when a ketone is added to Fehling’s solution?

  No visible change → stays blue
• How do you test for a carbonyl compound?

  Use Brady’s reagent - 2,4-dinitrophenylhydrazine; orange precipitate forms if present.
• What is in Tollens’ reagent?

  Silver complex ions in colourless solution.
• What happens when an aldehyde is added to Tollen’s reagent?

  Silver mirror forms as Ag+ reduced to Ag (s)
• What happens when a ketone is added to Tollen’s reagent?

  No visible change
• What is another oxidising agent for alcohols and aldehydes? What change in colour does this undergo?

  Acidified potassium dichromate (VI) - H2SO4 and K2Cr2O7; colour change from orange to green.
• What is a reducing agent for aldehydes and ketones? What ions does this release in solution?

  NaBH4 (sodium tetrahydridoborate (III)), releases an H- ion
• Draw and name a mechanism for the reduction of an aldehyde.

  • Mechanism: Nucleophilic addition
  • Nucleophile attacks carbonyl carbon
  • Forms an alcohol

  
• Write an equation for the reduction of pentan-2-one and for 3-methylbutanal.

  CH3COCH2CH2CH3 + 2[H] → CH3CH(OH)CH2CH2CH3; CH3CH2CH2(CH3)CHO + 2[H] → CH3CH2CH2(CH3)CH2OH
• How do you convert an aldehyde to form a carboxylic acid?

  Oxidation of aldehydes using Cr2O7 2-/H+ (i.e. K2Cr2O7/H2SO4)
• Write out the mechanism for the nucleophilic substitution reaction of carbonyl compound with NaBH4.

  • Nucleophile (H-) attacks carbonyl carbon
  • Forms a tetrahedral intermediate
  • Protonation leads to the alcohol product