Chapter 26 - Carbonyls and Carboxylic Acids

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6 Terms

1
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Describe structure of aldehyde & example

  • In aldehyde the carbonyl functional group is at the end of a carbon chain

  • Carbon atom of carbonyl group is attached to one or two hydrogen atoms

  • In its structural formula, the aldehyde group is written as CHO


Example: Methanal - used in solution to preserve biological specimens


2
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Describe structure of ketone & example

  • Carbonyl functional group is joined to two carbon atoms in the middle of the chain

  • In its structural formula, the ketone group is written as CO


Example: Propanone - used as industrial solvent and used in nail varnish removers


3
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Can aldehydes and ketones be oxidised and if so, what to?

  • Aldehydes can be oxidised to carboxylic acids when refluxed

  • Ketones are not oxidised

  • This is useful as we can distinguish between aldehydes and ketones using this fact


4
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Why do carbonyl compounds undergo nucleophilic addition rather than electrophilic like alkenes

  • Alkenes have a C=C double bond which is non-polar

  • Carbonyl compounds have a C=O double bond which is polar

  • Oxygen is more electronegative than carbon so electron density lies towards the oxygen so the oxygen end is slightly negative whilst the carbon end is slightly positive

  • Due to polarity, a nucleophile is attracted to and attacks the slightly positive carbon atom


5
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What reducing agent are aldehydes and ketones reduced with and what are they reduced to

  • They are reduced with the reducing agent NaBH4

  • Aldehydes are reduced to primary alcohols

  • Ketones are reduced to secondary alcohols


6
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How does the reaction work, what is formed and why is the reaction between carbonyl compounds and hydrogen cyanide (HCN) useful?

  • Hydrogen cyanide is colourless, poisonous and boils slightly above room temperature so can not be used safely hence sodium cyanide and sulfuric acid are used to provide the hydrogen cyanide, although the reaction can still be potentially hazardous

  • Hydroxynitrile is formed which has 2 functional groups, -OH and C-N (triple bond)

  • The reaction is useful as we can increase the length of the carbon chain