Carbonyl compounds

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Carbonyl compounds

  • they are Aldehydes and Ketones 
  • their functional groups are what give them their properties- make sure you can identify them
  • (
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Carbonyl compounds

  • learn how to draw them accuratly 
  • they have lower BPs than alcohols as there is no hydrogen bonding between Aldhyde/ Ketone molecules
  • Please note that they can form hydrogen bonds with water but only one 
  • shorter aldehydes are able to be dissolved in water however this is not favourable for longer molecules due to the cost of making the hydrogen bond and breaking the london forces
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Reduction of carbonyl compounds

during your study of alcohols you willl have learn how aldehydes and ketones can be formed by oxidatiion reactions we are about to look at the reverse reaction 

lithium aluminum hydride in dry ether acts as a source of hydride (H-) ions which act as a nucleophile . the reaction must be warmed and HCL added so that the oxygen can be protonated and the alcohol formed


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Tests for carbonyl compounds

2,4 dinitrophenylhydrazine (2,4DNP or brady's reagent) and the substance to be tested if the result does not form immediately warm and add some sulphuric acid and allow to cool

  • A positive test will show a yellow/orange precipitate/crystals
  • A negative result will leave a clear orange liquid

it is possible to work out the individual carbonyl compound by working out the melting point of the prepcitate

Fehlings will give a red/brown precipitate if an aldehyde is present there will be no change for a ketone

Tollens reagent will give a 'silver' mirror if aldehyde is present no change for ketones

Oxidation with potassium/ sodium dichromate and conc sulphuric acid no change with a ketone but a colour change to green will occur if an aldehyde is present as it can be oxidised to a carboxylic acid

Be familiar with the ionic equations of the last test

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one last test

The iodoform test

this test for a methyl ketone or a methyl aldehyde NaOH and KI in solution as well as your sample apositive result will form a Yellow prepciptate which smells of antiseptic( think of TCP)

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