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Organic Chemistry, 5th ed.

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Presentation on theme: "Organic Chemistry, 5th ed."— Presentation transcript:

1 Organic Chemistry, 5th ed.
Marc Loudon Chapter 19 The Chemistry of Aldehydes and Ketones. Carbonyl-Addition Reactions Eric J. Kantorowski California Polytechnic State University San Luis Obispo, CA

2 Chapter 19 Overview 19.1 Nomenclature of Aldehydes and Ketones
19.2 Physical Properties of Aldehydes and Ketones 19.3 Spectroscopy of Aldehydes and Ketones 19.4 Synthesis of Aldehydes and Ketones 19.5 Introduction to Aldehyde and Ketone Reactions 19.6 Basicity of Aldehydes and Ketones 19.7 Reversible Addition Reactions of Aldehydes and Ketones 19.8 Reduction of Aldehydes and Ketones to Alcohols 19.9 Reactions of Aldehydes and Ketones with Grignard and Related Reagents 19.10 Acetals and Their Use of Protecting Groups

3 Chapter 19 Overview 19.11 Reactions of Aldehydes and Ketones with Amines 19.12 Reduction of Carbonyl Groups to Methylene Groups 19.13 The Wittig Alkene Synthesis 19.14 Oxidation of Aldehydes to Carboxylic Acids 19.15 Manufacture and Use of Aldehydes and Ketones

4 Aldehydes and ketones have the following general structure
Carbonyl Compounds Aldehydes and ketones have the following general structure 19.1 Nomenclature of Aldehydes and Ketones

5 Carbonyl Compounds 19.1 Nomenclature of Aldehydes and Ketones

6 Common Nomenclature 19.1 Nomenclature of Aldehydes and Ketones

7 Prefixes Used in Common Nomenclature
19.1 Nomenclature of Aldehydes and Ketones

8 Common Nomenclature 19.1 Nomenclature of Aldehydes and Ketones

9 Substitutive Nomenclature
19.1 Nomenclature of Aldehydes and Ketones

10 Substitutive Nomenclature
19.1 Nomenclature of Aldehydes and Ketones

11 Most simple aldehydes and ketones are liquids
Physical Properties Most simple aldehydes and ketones are liquids 19.2 Physical Properties of Aldehydes and Ketones

12 Strong C=O stretch: 1700 cm-1
IR Spectroscopy Strong C=O stretch: 1700 cm-1 19.3 Spectroscopy of Aldehydes and Ketones

13 Conjugation with a p bond lowers the absorption frequency
IR Spectroscopy Conjugation with a p bond lowers the absorption frequency 19.3 Spectroscopy of Aldehydes and Ketones

14 IR Spectroscopy The C=O stretching frequency in small-ring ketones is affected by ring size 19.3 Spectroscopy of Aldehydes and Ketones

15 However, the electronegative O increases this shift farther downfield
1H NMR Spectroscopy The reason for the large d value for aldehydic protons is similar to that for vinylic protons However, the electronegative O increases this shift farther downfield 19.3 Spectroscopy of Aldehydes and Ketones

16 Aldehyde and ketone C=O: d 190-220 a-Carbons: d 30-50
13C NMR Spectroscopy Aldehyde and ketone C=O: d a-Carbons: d 30-50 19.3 Spectroscopy of Aldehydes and Ketones

17 p → p*: 150 nm (out of the operating range)
UV/Vis Spectroscopy p → p*: 150 nm (out of the operating range) n → p*: nm (much weaker) 19.3 Spectroscopy of Aldehydes and Ketones

18 UV/Vis Spectroscopy 19.3 Spectroscopy of Aldehydes and Ketones

19 Mass Spectrometry 19.3 Spectroscopy of Aldehydes and Ketones

20 What accounts for the m/z = 58 peak?
Mass Spectrometry What accounts for the m/z = 58 peak? 19.3 Spectroscopy of Aldehydes and Ketones

21 There must be an available g-H
Mass Spectrometry The McLafferty rearrangement involves a hydrogen transfer via a transient six-membered ring There must be an available g-H 19.3 Spectroscopy of Aldehydes and Ketones

22 Summary of Aldehyde and Ketone Preparation
1. Oxidation of alcohols 2. Friedel-Crafts acylation 3. Hydration of alkynes 4. Hydroboration-oxidation of alkynes 5. Ozonolysis of alkenes 6. Periodate cleavage of glycols 19.4 Synthesis of Aldehydes and Ketones

23 Carbonyl-Group Reactions
Reactions with acids Addition reactions Oxidation of aldehydes 19.5 Introduction to Aldehyde and Ketone Reactions

24 Basicity of Aldehydes and Ketones
The carbonyl oxygen is weakly basic One resonance contributor reveals that carbocation character exists The conjugate acids of aldehydes and ketones may be viewed as a-hydroxy carbocations 19.6 Basicity of Aldehydes and Ketones

25 Basicity of Aldehydes and Ketones
a-hydroxy and a-alkoxy carbocations are significantly more stable than ordinary carbocations (by ~100 kJ mol-1) 19.6 Basicity of Aldehydes and Ketones

26 Addition Reactions One of the most typical reactions of aldehydes and ketones is addition across the C=O 19.7 Reversible Addition Reactions of Aldehydes and Ketones

27 Mechanism of Carbonyl-Addition Reactions
19.7 Reversible Addition Reactions of Aldehydes and Ketones

28 Addition Reactions The addition of a nucleophile to the carbonyl carbon is driven by the ability of oxygen to accept the unshared electron pair 19.7 Reversible Addition Reactions of Aldehydes and Ketones

29 The nucleophile attacks the unoccupied p* MO (LUMO) of the C=O
Addition Reactions The nucleophile attacks the unoccupied p* MO (LUMO) of the C=O 19.7 Reversible Addition Reactions of Aldehydes and Ketones

30 Addition Reactions The second mechanism for carbonyl addition takes place under acidic conditions 19.7 Reversible Addition Reactions of Aldehydes and Ketones

31 Equilibria in Carbonyl-Addition Reactions
The equilibrium for a reversible addition depends strongly on the structure of the carbonyl compound 1. Addition is more favorable for aldehydes 2. Addition is more favorable if EN groups are near the C=O 3. Addition is less favorable when groups that donate electrons by resonance to the C=O are present 19.7 Reversible Addition Reactions of Aldehydes and Ketones

32 Equilibrium Constants for Hydration
19.7 Reversible Addition Reactions of Aldehydes and Ketones

33 Relative Carbonyl Stability
19.7 Reversible Addition Reactions of Aldehydes and Ketones

34 For example, alkyl groups stabilize carbocations more than hydrogens
Carbonyl Stability Any feature that stabilizes carbocations will impart greater stability to the carbonyl group For example, alkyl groups stabilize carbocations more than hydrogens Hence, alkyl groups will discourage addition reactions to the carbonyl group 19.7 Reversible Addition Reactions of Aldehydes and Ketones

35 Resonance can also add stability to the carbonyl group
Carbonyl Stability Resonance can also add stability to the carbonyl group However, EN groups make the addition reaction more favorable 19.7 Reversible Addition Reactions of Aldehydes and Ketones

36 Rates of Carbonyl-Addition Reactions
Relative rates can be predicted from equilibrium constants Compounds with the most favorable addition equilibria tends to react most rapidly General reactivity: formaldehyde > aldehydes > ketones 19.7 Reversible Addition Reactions of Aldehydes and Ketones

37 Reduction with LiAlH4 and NaBH4
19.8 Reduction of Aldehydes and Ketones to Alcohols

38 LiAlH4 serves as a source of hydride ion (H:-)
Reduction with LiAlH4 LiAlH4 serves as a source of hydride ion (H:-) LiAlH4 is very basic and reacts violently with water; anhydrous solvents are required 19.8 Reduction of Aldehydes and Ketones to Alcohols

39 Like other strong bases, LiAlH4 is also a good nucleophile
Reduction with LiAlH4 Like other strong bases, LiAlH4 is also a good nucleophile Additionally, the Li+ ion is a built-in Lewis-acid 19.8 Reduction of Aldehydes and Ketones to Alcohols

40 Each of the remaining hydrides become activated during the reaction
Reduction with LiAlH4 Each of the remaining hydrides become activated during the reaction 19.8 Reduction of Aldehydes and Ketones to Alcohols

41 Hydrogen bonding then serves to activate the carbonyl group
Reduction with NaBH4 Na+ is a weaker Lewis acid than Li+ requiring the use of protic solvents Hydrogen bonding then serves to activate the carbonyl group 19.8 Reduction of Aldehydes and Ketones to Alcohols

42 Reduction with LiAlH4 and NaBH4
Reactions by these and related reagents are referred to as hydride reductions These reactions are further examples of nucleophilic addition 19.8 Reduction of Aldehydes and Ketones to Alcohols

43 Selectivity with LiAlH4 and NaBH4
NaBH4 is less reactive and hence more selective than LiAlH4 LiAlH4 reacts with alkyl halides, alkyl tosylates, and nitro groups, but NaBH4 does not 19.8 Reduction of Aldehydes and Ketones to Alcohols

44 Reduction by Catalytic Hydrogenation
Hydride reagents are more commonly used However, catalytic hydrogenation is useful for selective reduction of alkenes 19.8 Reduction of Aldehydes and Ketones to Alcohols

45 Grignard Addition Grignard reagents with carbonyl groups is the most important application of the Grignard reagent in organic chemistry 19.9 Reactions of Aldehydes and Ketones with Grignard and Related Reagents

46 The addition is irreversible due to this basicity
Grignard Addition R-MgX reacts as a nucleophile; this group is also strongly basic behaving like a carbanion The addition is irreversible due to this basicity 19.9 Reactions of Aldehydes and Ketones with Grignard and Related Reagents

47 Organolithium and Acetylide Reagents
These reagents react with aldehydes and ketones analogous to Grignard reagents 19.9 Reactions of Aldehydes and Ketones with Grignard and Related Reagents

48 Importance of the Grignard Addition
This reaction results in C-C bond formation The synthetic possibilities are almost endless 19.9 Reactions of Aldehydes and Ketones with Grignard and Related Reagents

49 Importance of the Grignard Addition
19.9 Reactions of Aldehydes and Ketones with Grignard and Related Reagents

50 Preparation and Hydrolysis of Acetals
Acetal: A compound in which two ether oxygens are bound to the same carbon 19.10 Acetals and Their Use of Protecting Groups

51 Preparation and Hydrolysis of Acetals
Use of a 1,2- or 1,3-diol leads to cyclic acetals Only one equivalent of the diol is required 19.10 Acetals and Their Use of Protecting Groups

52 Preparation and Hydrolysis of Acetals
19.10 Acetals and Their Use of Protecting Groups

53 Preparation and Hydrolysis of Acetals
Acetal formation is reversible The presence of acid and excess water allows acetals to revert to their carbonyl form Acetals are stable in basic and neutral solution 19.10 Acetals and Their Use of Protecting Groups

54 Hemiacetals normally cannot be isolated
Exceptions include simple aldehydes and compounds than can form 5- and 6-membered rings 19.10 Acetals and Their Use of Protecting Groups

55 Hemiacetals 19.10 Acetals and Their Use of Protecting Groups

56 Protecting Groups A protecting group is a temporary chemical disguise for a functional group preventing it from reacting with certain reagents 19.10 Acetals and Their Use of Protecting Groups

57 Protecting Groups 19.10 Acetals and Their Use of Protecting Groups

58 Reactions with Primary Amines
Imines are sometimes called Schiff bases 19.11 Reactions of Aldehydes and Ketones with Amines

59 Reactions with Primary Amines
The dehydration of water is typically the rate-limiting step 19.11 Reactions of Aldehydes and Ketones with Amines

60 Derivatives Before the advent of spectroscopy, aldehydes and ketones were characterized as derivatives 19.11 Reactions of Aldehydes and Ketones with Amines

61 Some Imine Derivatives
19.11 Reactions of Aldehydes and Ketones with Amines

62 Reactions with Secondary Amines
Like imine formation, enamine formation is reversible 19.11 Reactions of Aldehydes and Ketones with Amines

63 Reactions with Secondary Amines
19.11 Reactions of Aldehydes and Ketones with Amines

64 Reactions with Tertiary Amines
Tertiary amines do not react with aldehydes or ketones to form stable derivatives They are good nucleophiles, but the lack of an N-H prevents conversion to a stable compound 19.11 Reactions of Aldehydes and Ketones with Amines

65 Reduction of Aldehydes and Ketones
Complete reduction to a methylene (-CH2-) group is possible by two different methods Wolff-Kishner reduction: 19.12 Reduction of Carbonyl Groups to Methylene Groups

66 Reduction of Aldehydes and Ketones
The Wolff-Kishner reduction takes place under highly basic conditions It is an extension of imine formation 19.12 Reduction of Carbonyl Groups to Methylene Groups

67 Reduction of Aldehydes and Ketones
Clemmensen reduction: This reduction occurs under acidic conditions The mechanism is uncertain 19.12 Reduction of Carbonyl Groups to Methylene Groups

68 The Wittig Alkene Synthesis
This reaction is completely regioselective, assuring the location of the alkene 19.13 The Wittig Alkene Synthesis

69 The Wittig Alkene Synthesis
Occurs via an addition-elimination sequence using a phosphorous ylide An ylid (or ylide) is any compound with opposite charges on adjacent, covalently bound atoms 19.13 The Wittig Alkene Synthesis

70 The Wittig Alkene Synthesis

71 Preparation of the Wittig Reagent
Any alkyl halide that readily participates in SN2 reactions can be used 19.13 The Wittig Alkene Synthesis

72 The Wittig Alkene Synthesis
Retrosynthetically Stereochemistry 19.13 The Wittig Alkene Synthesis

73 Carboxylic Acids from Aldehydes
The hydrate is the species oxidized 19.14 Oxidation of Aldehydes to Carboxylic Acids

74 Carboxylic Acids from Aldehydes
This is known as the Tollen’s test A positive indicator for an aldehyde is the deposition of a metallic silver mirror on the walls of the reaction flask 19.14 Oxidation of Aldehydes to Carboxylic Acids

75 Production and Use of Aldehydes
The most important commercial aldehyde is formaldehyde Its most important use is in the synthesis of phenol-formaldehyde resins 19.15 Manufacture and Use of Aldehydes and Ketones

76 Production and Use of Ketones
The most important commercial ketone is acetone It is co-produced with phenol by the autoxidation-rearrangement of cumene 19.15 Manufacture and Use of Aldehydes and Ketones

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