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Chapter 19 The Chemistry of Aldehydes and Ketones. Carbonyl-Addition Reactions

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Organic Chemistry, 5th ed. Marc Loudon Chapter 19 The Chemistry of Aldehydes and Ketones. Carbonyl-Addition Reactions Eric J. Kantorowski California Polytechnic State ... – PowerPoint PPT presentation

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Title: Chapter 19 The Chemistry of Aldehydes and Ketones. Carbonyl-Addition Reactions


1
Chapter 19 The Chemistry of Aldehydes and
Ketones. Carbonyl-Addition Reactions
Organic Chemistry, 5th ed. Marc Loudon
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
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
Physical Properties
  • Most simple aldehydes and ketones are liquids

19.2 Physical Properties of Aldehydes and Ketones
12
IR Spectroscopy
  • Strong CO stretch 1700 cm-1

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

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

19.3 Spectroscopy of Aldehydes and Ketones
15
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
13C NMR Spectroscopy
  • Aldehyde and ketone CO d 190-220
  • a-Carbons d 30-50

19.3 Spectroscopy of Aldehydes and Ketones
17
UV/Vis Spectroscopy
  • p ? p 150 nm (out of the operating range)
  • n ? p 260-290 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
Mass Spectrometry
  • What accounts for the m/z 58 peak?

19.3 Spectroscopy of Aldehydes and Ketones
21
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 CO

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
Addition Reactions
  • The nucleophile attacks the unoccupied p MO
    (LUMO) of the CO

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 CO
  • 3. Addition is less favorable when groups that
    donate electrons by resonance to the CO 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
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
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 gt aldehydes gt
    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
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
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
Reduction with LiAlH4
  • Each of the remaining hydrides become activated
    during the reaction

19.8 Reduction of Aldehydes and Ketones to
Alcohols
41
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
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
  • 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
19.13 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 Tollens 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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