1. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Recognise and name aldehydes and ketones.

2. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original The carbonyl functional group

3. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Formation of the C=O group π -bond

4. Naming aldehydes See p. 20 A2 text book. In an aldehyde the carbon atom of the carbonyl group is joined to at least 1 hydrogen atom. Aldehydes end in ‘al’. The parent chain is the longest unbranched carbon chain present in the molecule. The carbonyl C atom is always the 1 carbon in the chain.

5. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original 2-methylpentanal

6. Naming ketones See p. 21 A2 text book. In ketones the carbonyl group is in the middle of a chain with a C atom on either side. Ketones end in ‘one’. The parent chain is the longest chain containing the carbonyl group. The carbonyl is numbered with the smallest possible number.

7. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original The structure of 2-methylpentan-3-one

8. Aromatic aldehydes and ketones These contain the carbonyl functional group and a ring. The simplest aromatic aldehyde is? The simplest aromatic ketone is? Aromatic carbonyls contribute to the flavours and smells of many stone fruits, plums, peaches, cherries etc. Cinnamaldehyde is the characteristic smell and flavour of cinnamon. Phenylethanone resembles strawberries etc.

9. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Structures of benzaldehyde and phenylethanone

10. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Structure of cinnamaldehyde

11. Physical Properties of Carbonyl Compounds Aliphatic carbonyl compounds are generally less pleasant, particularly aldehydes which are described as lachrymatory. E.g. Heptan-2-one is responsible for the flavour of blue cheese. Lower members of both carbonyl series are soluble in water. Solubility decreases with increasing RMM. Volatility decreases with increasing RMM.

12. Volatility CompoundBP o C Ethanal20 Propane-42 Ethanol78

13. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Describe the oxidation of primary alcohols to form aldehydes and carboxylic acids. Describe the oxidation of secondary alcohols to form ketones. Describe the oxidation of aldehydes to form carboxylic acids.

14. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Ethanol oxidised to ethanal, and finally to ethanoic acid

15. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Propan-2-ol can be oxidised to propanone

16. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Oxidation of an aldehyde to a carboxylic acid

17. Oxidation Oxidation is: Gain of oxygen Loss of hydrogen Loss of electrons In the oxidation of alcohols or aldehydes, ion electron equations can be written which are more informative than the [O] symbol. See p. 23 in A2 text.

18. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Describe the reduction of carbonyl compounds to form alcohols. Outline the mechanism for nucleophilic addition reactions of aldehydes and ketones with hydrides.

19. Reduction of carbonyl compounds Aldehydes and ketones are made by the OXIDATION of alcohols. It follows that with a suitable reducing agent carbonyl compounds should be reduced back to alcohols. NaBH 4 is used with warming and water or ethanol as a solvent. The reaction can be considered as the addition of hydrogen across the double bond, though the actual reaction is nucleophilic addition using H - as the nucleophile.

20. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Reduction of an aldehyde produces a primary alcohol

21. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original The primary alcohol propan-1-ol and the aldehyde propanal

22. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Reduction of a ketone produces a secondary alcohol

23. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original NaBH 4 readily generates hydride ions

24. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Reduction of an aldehyde by nucleophilic addition

25. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Describe the use of 2,4-dinitrophenylhydrazine to detect a carbonyl group and to identify a carbonyl compound. Describe the use of Tollens’ reagent to detect the presence of an aldehyde group.

26. Test for the Presence of a Carbonyl Group 2,4-dinitrophenylhydrazine will give an orange precipitate with any carbonyl compound (not acids, esters etc). The reaction is an addition/elimination reaction or condensation reaction which involves addition across the double bond followed by loss of water. 2,4-DNP or Brady’s reagent is used because the big molecule gives better precipitates of the hydrazone derivative with distinct and diagnostic melting points.

27. Test for the Presence of a Carbonyl Group If the hydrazone derivative is recrystallised from hot ethanol the melting point determination can be used to identify an unknown carbonyl compound.

28. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Reaction of propanal with 2,4-dinitrophenylhydrazine

29. Aldehyde or Ketone? Aldehydes are oxidised to carboxylic acids with mild oxidising agents but ketones are unaffected. This can be used to distinguish between them. Tollen’s Reagent – ammoniacal silver nitrate, will oxidise an aldehyde when left to stand in mildly warm,not hot water to a silver mirror. The oxidation of the aldehyde is shown after this but the oxidising agent – Ag + ions are reduced to metallic silver. Ag + (aq) + e - → Ag (s)

30. Week 3 © Pearson Education Ltd 2009 This document may have been altered from the original Oxidation of an aldehyde using Tollens’ reagent