Aldehydes and Ketones

• Both are carbonyl compounds and both have the functional group C=O.
• Difference between aldehydes and ketones is that they have their carbonyl groups in different positions.
• Aldehydes have their carbonyl group at the end of the C chain.
• Ketones have their carbonly group in the middle of the C chain.
• Aldehydes: -al
• Ketones: -one

• A colourless solution of silver nitrate dissolved in aqueous ammonia.
• If heated in test tube with an aldehyde, silver mirror forms.
• As aldehyde is oxidised, the diaminesilver ions in Tollen's reagent are reduced, producing silver and ammonia:

Ketones do not react with Tollens'

• Blue solution of complexed copper (II) ions dissolved in sodium hydroxide.
• If heated with an aldehyde the copper (II) ions are reduced to a brick-red precipitate of copper (I) oxide:

Ketones also do not react with Fehling's.

• Primary alcohols can be oxidised to produce aldehydes and carboxylic acids, and secondary alcohols can be oxidised to make ketones.
• Using a reducing agent you can reduce these reactions.
• NaBH4 (sodium tetrahydridoborate(III) or sodium borohydride is usually the reducing agent used.
• In equations, [H] is often used to indicate a hydrogen from a reducing agent.

Reduction of an aldehyde to a primary alcohol:

Reduction of a ketone to a secondary alcohol:

• There are tests to distinguish between aldehydes and ketones. They work on the idea that an aldehyde can be easily oxidised into a carboxylic acid, but a ketone cannot.
• Aldehydes can be easily oxidised to carboxylic acid because there is a H attached to the carbonyl group:
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The only way to oxidise a ketone would be to break a c-c bond so ketones are not easily oxidised:

As aldehyde oxidised, another compound reduced- so reagent used that changes colour as it is reduced. 2 reactants that can be used are Tollens' and Fehling's.