3.5.1

Carbonyls

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Aldehydes and Ketones

The carbonyl functional group is a carbon double bonded to an oxygen atom. It is present in aldehydes, ketones, carboxylic acids, and amides.

Illustrative background for Redox behaviourIllustrative background for Redox behaviour ?? "content

Redox behaviour

  • Aldehydes can be oxidised to carboxylic acids or reduced to primary alcohols.
  • Ketones cannot be oxidised but can be reduced to a secondary alcohol.
Illustrative background for Identifying aldehydes and ketonesIllustrative background for Identifying aldehydes and ketones ?? "content

Identifying aldehydes and ketones

  • There are three tests: Benedict’s solution, Fehling’s solution, or Tollen’s reagent.
    • Benedict’s and Fehling’s solution will turn from blue to brick red in the presence of an aldehyde, but do nothing with a ketone.
    • Tollen’s reagent will coat the test-tube in a silver mirror in the presence of an aldehyde, but stay clear with a ketone.

Carbonyls and Reduction

Carbonyls can be reduced to alcohols.

Illustrative background for Hydride reductionIllustrative background for Hydride reduction ?? "content

Hydride reduction

  • The mechanism for the reduction of an aldehyde by a hydride ion is shown.
    • Note how the H is acting as a nucleophile as it attacks the carbonyl.
  • The mechanism is called a nucleophilic addition reaction.
    • It is used here to reduce aldehydes and ketones to primary and secondary alcohols.
Illustrative background for Sodium borohydrideIllustrative background for Sodium borohydride ?? "content

Sodium borohydride

  • We get the H from NaBH4 - sodium borohydride.
    • It is called a hydride source.

Key points

  • You can’t have a free hydride ion - it’s too reactive.
    • The reactive ion is actually the B-H bond, but you can draw it as a H- ion in mechanisms.
  • NaBH4 will only reduce carbonyls once because the alcohol is less reactive. The reasons for that are complex!

Jump to other topics

1Physical Chemistry

1.1Atoms, Molecules & Stoichiometry

1.2Atomic Structure

1.3Chemical Bonding

1.4States of Matter

1.5Chemical Energetics

1.6Electrochemistry

1.7Equilibria

1.8Partition Coefficient

1.9Reaction Kinetics

2Inorganic Chemistry

3Organic Chemistry & Analysis

3.1Introduction to Organic Chemistry

3.2Hydrocarbons

3.3Halogen Derivatives

3.4Hydroxy Compounds

3.5Carbonyl Compounds

3.6Carboxylic Acids & Derivatives

3.7Nitrogen Compounds

3.8Polymerisation

3.9Analytical Techniques

3.10Organic Synthesis

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