13 aldehydes-and-ketones

1. Chapter 13 Aldehydes and Ketones

2. 1. Structure The carbonyl group is a double bond between oxygen and carbon. Carbonyl compounds include: Aldehydes : at least one hydrogen bonded to the carbonyl carbon Ketones : no hydrogens bonded to the carbonyl carbon. carboxylic acids and amides. [Tune in NEXT chapter…]

3. 1. Properties The carbonyl group is polar. Intermolecular forces in carbonyl compounds are stronger than in alkanes (nonpolar) or ethers (only slightly polar). weaker than in alcohols, which are polar and can hydrogen bond.

4. 1. Boiling points Structure Name Molar mass Boiling point CH 3 CH 2 CH 2 CH 3 butane 58 -0.5 o C CH 3 -O-CH 2 CH 3 methoxyethane 60 7.0 o C CH 3 CH 2 CH 2 -OH 1-propanol 60 97.2 o C O || CH 3 CH 2 -C-H propanal 58 49 o C O || CH 3 -C-CH 3 propanone 58 56 o C ♫

5. 1. Solubility There is no hydrogen bonding between two carbonyl groups.

6. 1. Solubility Aldehydes and ketones can hydrogen bond with water. Aldehydes and ketones with five or fewer carbon atoms are fairly soluble in water. Large aldehydes and ketones dissolve only in nonpolar solvents. ♫

7. 1. Solubility

8. 1. Solubility in water—general guidelines Molecules with polar groups tend to be more soluble in water. Molecules that can hydrogen bond with water are more soluble than those than cannot. Increasing the number of polar groups on a molecule increases its water solubility. Increasing the number of possibilities for hydrogen bonding increases solubility in water. Increasing the molar mass of a molecule decreases its water solubility.

9. 2. Nomenclature Naming aldehydes The parent compound is named for the longest continuous chain containing the carbonyl group. The final –e of the parent alkane is replaced with –al . The chain is numbered beginning at the carbonyl carbon. Substituents are named and numbered as usual. The aldehyde is always carbon 1, so no number is used for the carbonyl group.

10. 2. Nomenclature The simplest aldehydes Draw structures for 7,8-dibromooctanal trans -2-hexenal (component of olive oil) methanal ethanal pencast

11. 2. Nomenclature Name the following compounds. pencast ♫

12. 2. Nomenclature Ketones The rules are analogous to the rules for aldehydes. The –e ending of the parent alkane is changed to –one . The location of the carbonyl is indicated with a number. [This number is never 1- because that would be an aldehyde!] The longest carbon chain is numbered to give the carbonyl the lowest possible number.

13. 2. Nomenclature The simplest ketones need no number for the carbonyl. (Why?) Draw structures for the following compounds. 2-fluorocyclohexanone 3-chloro-2-pentanone propanone butanone pencast ♫

14. 2. Nomenclature Name the following compounds. pencast

15. 3. Important aldehydes and ketones What is the relationship between embalming fluid and methanol poisoning? What is the I.U.P.A.C. name of the following component of lemongrass? pencast ♫

16. 3. Important aldehydes and ketones What is the I.U.P.A.C. name for cinnamaldehyde? Chanel No. 5 became famous for containing synthetic aldehydes “in copious quantities”.* * Perfume Shrine pencast Follow the link for a fun description of properties of aldehydes and ketones.

17. 3. Important aldehydes and ketones Aldehydes in perfumery heptanal: naturally occuring in clary sage and possessing a herbal green odour octanal: orange-like nonanal: smelling of roses decanal: powerfully evocative of orange rind citral (a more complicated 10-carbon aldehyde): odor of lemons undecanal: naturally present in coriander leaf oil unsaturated undecen-1-al lauryl aldehyde (12 carbons): evocative of lilacs or violets

18. 4. Reactions--oxidation Preparation is usually by oxidation of an alcohol. Aldehydes are produced from primary alcohols .

19. 4. Reactions--oxidation Ketones are produced from secondary alcohols . Tertiary alcohols don’t undergo oxidation (no –H to lose). ♫

20. 4. Reactions--oxidation Oxidation of aldehydes and ketones Aldehydes can be oxidized to carboxylic acids. loss of a bond to H, gain of a bond to O

21. 4. Reactions--oxidation Oxidation of aldehydes and ketones Ketones can’t be oxidized further. N.R. (no –H to lose) ♫

22. 4. Reactions--oxidation Tollen’s test is used to distinguish between aldehydes and ketones based on their ability to be oxidized. When one substance is oxidized, another must be reduced. + Ag(NH 3 ) 2 +  + Ag o Tollen’s reagent elemental silver

23. 4. Reactions--oxidation + Ag(NH 3 ) 2 +  + Ag o elemental silver If an aldehyde is present, a “silver mirror” forms on the inside of the glass container. If a ketone is present, there is no reaction because it won’t undergo oxidation.

24. 4. Reactions--oxidation The same process used in Tollen’s test used to be used to produce silvered mirrors. This is an article published in 1911 describing the process, if you are interested! Go here to see a 2-liter flask turned into a mirror. For EXTRA CREDIT , explain what precautions need to be taken when the Tollen’s test is carried out. You’ll have to watch the video. Post your answer in the Module 4 Journal Answers journal with the tag Tollen.

25. 4. Reactions--oxidation Draw the structure of the following compounds and their oxidation products. 2-methyl-2-propanol 2-nonanol 1-decanol pencast ♫

26. 4. Reactions--oxidation What reaction will pentanal undergo, if any, with Tollen’s reagent? pencast ♫

27. 4. Reactions--oxidation Benedict’s test is used to distinguish between reducing and non-reducing sugars. A reducing sugar can be oxidized. The substance reduced is Cu +2 . reducing sugar + Cu +2  oxidized sugar + Cu 2 O

28. 4. Reactions--oxidation Benedict’s test + Cu +2  + Cu 2 O

29. 4. Reactions—blast from the past Can you remember Chapter 12? Preparation of alcohols by hydrogenation of aldehydes and ketones (slide 19)

30. 4. Reactions--reduction Hydrogenation is a reduction reaction . More bonds to hydrogen, fewer bonds to oxygen Reduction of an aldehyde or ketone requires a Ni, Pt, or Pd catalyst. [sound familiar?] Reduction of an aldehyde produces a primary alcohol. Reduction of a ketone produces a secondary alcohol.

31. 4. Reactions--reduction What is the product of reduction of 1-chloropropanone? 2-methylpropanal? pencast ♫

32. 4. Reactions--addition Take the time machine back to Chapter 11 now. Alkenes undergo addition reactions: Hydrogenation (addition of H 2 ) Halogenation (addition of X 2 ) Hydration (addition of H 2 O) Hydrohalogenation (addition of HX) General addition reaction

33. 4. Reactions--addition Addition of an alcohol to an aldehyde: H +

34. 4. Reactions--addition The product is called a hemiacetal (-OH and –OR attached to the same carbon). Hemiacetals are very reactive. They react with an additional alcohol molecule, losing –OH and adding another –OR.

35. 4. Reactions--addition The final product is an acetal (2 –OR groups attached to one carbon). hemiacetal acetal

36. 4. Reactions--addition Ketones undergo analogous addition reactions with alcohols. The initial product is a reactive hemiketal (two –R groups, one –OH, and one –OR). An additional –OR group is added to the hemiketal to produce a ketal . hemiketal ketal

37. 4. Reactions--addition

38. 4. Reactions Hemiacetal, acetal, hemiketal, or ketal? ♫

39. 4. Reactions Monosaccharide addition reactions 1 2 3 4 5 6 ] alcohol aldehyde D -glucose ]

40. 1 2 3 4 5 6 4. Reactions Monosaccharide addition reactions The cyclic form is more stable than the linear form and no further oxidation takes place in this case. Hemiacetal : one –H one –OH one –OR one -R

41. 4. Reactions: keto-enol tautomers Tautomers differ from each other in the placement of one hydrogen and one double bond. The two forms exist in an equilibrium mixture, mostly in the keto form, which is more stable. Keto form ( keto ne) Enol form (alcoh ol + alk en e)

42. 4. Reactions: keto-enol tautomers Draw the keto and enol forms of propanone. propanal. pencast

43. 4. Reactions: aldol condensation In an aldol condensation , aldehydes or ketones react to make a larger molecule by forming a new carbon-carbon bond between two molecules. + OH - or enzyme

44. 4. Reactions: aldol condensation Write an equation for the aldol condensation of two molecules of propanal. pencast