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Chapter 18: Ketones and Aldehydes. Classes of Carbonyl Compounds.

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Presentation on theme: "Chapter 18: Ketones and Aldehydes. Classes of Carbonyl Compounds."— Presentation transcript:

1 Chapter 18: Ketones and Aldehydes

2 Classes of Carbonyl Compounds

3 Carbonyl C=O bond is shorter, stronger and more polar than C=C bond in alkenes

4 Nomenclature: Ketone Number chain so the carbonyl carbon has the lowest number Replace “e” with “one”

5 Nomenclature: Cyclic Ketone Carbonyl carbon is #1

6 Nomenclature: Aldehydes Carbonyl carbon is #1 Replace “e” with “al” If aldehyde is attached to ring, suffix “carbaldehyde” is used

7 Nomenclature With higher-priority functional groups, ketone is “oxo” and an aldehyde is a “formyl” group Aldehydes have higher priority than ketones

8 Nomenclature- Common Names: Ketones Name alkyl groups attached to carbonyl Use lower case Greek letters instead of numbers

9 Nomenclature

10 Boiling Points Ketones and aldehydes are more polar. Have higher boiling point that comparable alkanes or ethers

11 Solubility: Ketones and Aldehydes Good solvent for alcohols Acetone and acetaldehyde are miscible in water

12 Formaldehyde Gas at room temperature

13 IR Spectroscopy Strong C=O stretch around 1710 cm -1 (ketones) or 1725 cm -1 (simple aldehydes) C-H stretches for aldehydes: 2710 and 2810 cm -1

14 IR Spectroscopy Conjugation lowers carbonyl frequencies to about 1685 cm -1 Rings with ring strain have higher C=O frequencies

15 Proton NMR Spectra Aldehyde protons normally around δ9-10 Alpha carbon around δ2.1-2.4

16 Carbon NMR Spectra

17 Mass Spectrometry (MS)



20 McLafferty Rearrangement Net result: breaking of the  bond and transfer of a proton from the  carbon to oxygen

21 Ultraviolet Spectra of Conjugated Carbonyls Have characteristic absorption in UV spectrum Additional conjugate C=C increases max about 30 nm, additional alkyl groups increase about 10nm

22 Carbonyl Electronic Transitions

23 Industrial Uses Acetone and methyl ethyl ketone are common solvents Formaldehyde is used in polymers like Bakelite and other polymeric products  Used as flavorings and additives for food

24 Industrial Uses

25 Synthesis of Aldehydes and Ketones The alcohol product of a Grignard reaction can be oxidized to a carbonyl

26 Synthesis of Aldehydes and Ketones Pyridinium chlorochromate (PCC) or a Swern oxidation takes primary alcohols to aldehydes

27 Synthesis of Aldehydes and Ketones Alkenes can be oxidatively cleaved by ozone, followed by reduction

28 Synthesis of Aldehydes and Ketones Friedel-Crafts Acylation

29 Synthesis of Aldehydes and Ketones Hydration of Alkynes Involves a keto-enol tautomerization Mixture of ketones seen with internal alkynes

30 Synthesis of Aldehydes and Ketones Hydroboration-oxidation of alkyne Anti-Markovnikov addition

31 Synthesis Problem

32 Synthesis of Aldehydes and Ketones Organolithium + carboxylic acid  ketone (after dehydration)

33 Synthesis of Aldehydes and Ketones Grignard or organolithium reagent + nitrile  ketone (after hydrolysis)

34 Synthesis of Aldehydes and Ketones Reduction of nitriles with aluminum hydrides will afford aldehydes

35 Synthesis of Aldehydes and Ketones Mild reducing agent lithium aluminum tri(t- butoxy)hydride with acid chlorides

36 Synthesis of Aldehydes and Ketones Organocuprate (Gilman reagent) + acid chloride  ketone

37 Nucleophilic Addition Aldehydes are more reactive than ketones

38 Wittig Reaction Converts the carbonyl group into a new C=C bond Phosphorus ylide is used as the nucleophile

39 Wittig Reaction Phosphorus ylides are prepared from triphenylphosphine and an unhindered alkyl halide Butyllithium then abstracts a hydrogen from the carbon attached to phosphorus

40 Wittig Reaction- Mechanism Betaine formation Oxaphosphetane formation

41 Wittig Reaction- Mechanism Oxaphosphetane collapse

42 How would you synthesize the following molecule using a Wittig Reaction

43 Hydration of Ketones and Aldehydes In aqueous solution, a ketone or aldehyde is in equilibrium with it’s hydrate Ketones: equilibrium favors keto form

44 Hydration of Ketones and Aldehydes Acid-Catalyzed

45 Hydration of Ketones and Aldehydes Base-Catalyzed

46 Cyanohydrin Formation Base-catalyzed nucleophilic addition HCN is highly toxic

47 Formation of Imines Imines are nitrogen analogues of ketones and aldehydes Optimum pH is around 4.5

48 Formation of Imines- Mechanism

49 Condensations with Amines

50 Acetal Formation

51 Hemiacetal Formation- Mechanism Must be acid-catalyzed

52 Acetal Formation- Mechanism Must be acid-catalyzed

53 Hydrolysis of Acetals Acetals can be hydrolyzed by addition of dilute acid Excess of water drives equilibrium towards carbonyl formation

54 Cyclic Acetals Addition of diol produces cyclic acetal Reaction is reversible Used as a protecting group Stable in base, hydrolyze in acid

55 Cyclic Acetals- Protecting Group Acetals are stable in base, only ketone reduces Hydrolysis conditions protonate the alkoxide and restore the aldehyde

56 Oxidation of Aldehydes Easily oxidized to carboxylic acids

57 Tollens Test Involves a solution of silver-ammonia complex to the unknown compound If an aldehyde is present, its oxidation reduces silver ion to metallic silver

58 Reducing Reagents- Sodium Borohydride NaBH 4 can reduce ketones and aldehydes, not esters, carboxylic acids, acyl chlorides, or amides

59 Reducing Reagents- Lithium Aluminum Hydride LiAlH 4 can reduce any carbonyl

60 Reducing Reagents- Catalytic Hydrogenation Widely used in industry Raney nickel is finely divided Ni powder saturated with hydrogen gas Will attack alkene first, then carbonyl

61 Deoxygenation of Ketones and Aldehydes Clemmensen reduction or Wolff-Kishner reactions can deoxygenate ketones and aldehydes

62 Clemmensen Reduction Uses Zinc-Mercury amalgam in aqueous HCl

63 Wolff-Kishner Reduction Forms hydrazone, then needs heat with strong base like KOH or potassium tert-butoxide Use high-boiling solvent (ethylene glycol, diethylene glycol, or DMSO)

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