6.1.2 CARBONYL COMPOUNDS

• What is the functional group of carbonyl compounds?

  • C=O
• How do carbonyl compounds interact with water?

  They form hydrogen bonds between the lone electron pair on the oxygen atom and the δ+ region on the hydrogen atom.
• Why do aldehydes and ketones not form hydrogen bonds between their molecules?

  Because they do not have a δ+ hydrogen atom.
• What type of intermolecular forces exist between aldehydes and ketones?

  Van der Waals forces.
• What is Brady’s reagent used for?

  To test for the presence of a carbonyl group.
• What is the positive result when testing for a carbonyl group with Brady’s reagent?

  An orange precipitate forms.
• How can you identify a specific aldehyde or ketone after obtaining a precipitate with Brady’s reagent?

  By purifying the precipitate via recrystallization and measuring the melting point to compare with literature values.
• Which compounds do NOT give a positive result with Brady’s reagent?

  Carboxylic acids and esters.
• What is the chemical formula for potassium dichromate(VI)?

  K2Cr2O7
• What happens to potassium dichromate(VI) when it oxidizes alcohol?

  It is reduced from orange to green due to a change in the oxidation state of chromium ion.
• Which types of alcohols can be oxidized by potassium dichromate(VI)?

  Primary and secondary alcohols.
• What is the functional group of aldehydes?

  • CHO
• Where is the carbonyl group located in aldehydes?

  At the end of the carbon chain.
• What is Tollen’s reagent used for?

  To test for aldehydes.
• What happens when an aldehyde is warmed with Tollen’s reagent?

  The aldehyde is oxidized to a carboxylic acid and reduces Ag+ ions to Ag, forming a silver mirror.
• What is the result of warming an aldehyde with Fehling’s solution?

  The aldehyde is oxidized to a carboxylic acid, and the Cu2+ is reduced to Cu+, resulting in a blue to red precipitate.
• What is the reaction equation for the oxidation of ethanol to ethanal?


  $\text{ethanol} +$$[O] \rightarrow \text{ethanal} +$$\text{H}_2\text{O}$
• What is the reaction equation for the further oxidation of ethanal to ethanoic acid?


  $\text{ethanal} +$$[O] \rightarrow \text{ethanoic acid}$
• What is the functional group of ketones?

  • C=O
• Where is the carbonyl group located in ketones?

  In the middle of the carbon chain, attached to two other carbon atoms.
• How do ketones react with Tollen’s and Fehling’s reagents?

  They do not react with either Tollen’s or Fehling’s reagents.
• What is the reaction equation for the oxidation of propan-2-ol to propan-2-one?


  $\text{propan-2-ol} \rightarrow \text{propan-2-one} +$$\text{H}_2$
• What is the role of sodium borohydride (NaBH4) in nucleophilic addition reactions?

  It acts as a reducing agent.
• What is produced when a carbonyl compound undergoes nucleophilic addition with a hydride nucleophile?

  An alcohol is produced.
• What happens when dilute acid is added to the salt formed in nucleophilic addition reactions?

  It releases the alcohol from the salt.
• What is the product of nucleophilic addition when using a CN- nucleophile?

  A hydroxynitrile is produced.
• What is a consequence of using a CN- nucleophile in nucleophilic addition reactions?

  It produces optical isomers due to the formation of a chiral carbon center.
• How does the attack of a CN- nucleophile on a carbonyl compound lead to the formation of different enantiomers?


  The CN- nucleophile can attack from above or below the planar C=O bond, resulting in different enantiomers.
• What is the structure of a carbonyl group?

  C=O
• What is the functional group represented by -CO?

  Carbonyl group
• How do carbonyl compounds interact with water?

  They can form hydrogen bonds due to the lone electron pair on the oxygen atom.
• Why do aldehydes and ketones not form hydrogen bonds between their molecules?


  Because they do not have a δ+ hydrogen atom.
• What type of intermolecular forces exist between aldehydes and ketones?

  Van der Waals forces
• What is Brady’s reagent used for?

  • Test for presence of carbonyl group
  • Contains 2,4-dinitrophenylhydrazine (2,4-DNPH)
  • Undergoes condensation reaction with carbonyl compounds
• What indicates a positive result when testing for a carbonyl group with Brady's reagent?

  An orange precipitate forms.
• How can the precipitate from Brady's reagent be purified?

  By recrystallisation and measuring the melting point.
• What should the melting point of the purified precipitate be compared to?

  Literature values or 2,4-dinitrophenylhydrazones of common aldehydes and ketones.
• Do carboxylic acids and esters give a positive result with Brady's reagent?

  No, they do not.
• What is the chemical formula for potassium dichromate(VI)?

  K2Cr2O7
• What is the role of potassium dichromate(VI) in organic reactions?

  It acts as an oxidising agent for alcohols and aldehydes.