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Keynotes in Organic Chemistry

De
240 pages
The development of university organic chemistry curricula and the trend towards modularisation of chemistry courses has driven the need for smaller, highly focussed and accessible organic chemistry textbooks, which complement the very detailed “standard texts”, to guide students through the key principles of the subject.

This concise and accessible book provides organic chemistry notes for students studying chemistry and related courses at undergraduate level, covering core organic chemistry in a format ideal for learning and rapid revision. The material is organised so that fundamental concepts are introduced early, then built on to provide an overview of the essentials of functional group chemistry and reactivity, leading the student to a solid understanding of the basics of organic chemistry. Graphical presentation of information is central to the book, to facilitate the rapid assimilation, understanding and recall of critical concepts, facts and definitions.

Students wanting a comprehensive and accessible overview of organic chemistry to build the necessary foundations for a more detailed study will find this book an ideal source of the information they require. In addition, the structured presentation, highly graphical nature of the text and practice problems with outline answers will provide an invaluable framework and aid to revision for students preparing for examinations.

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CONTENTS
Preface
1. Structure and Bonding 1.1 Ionic, covalent, coordinate and hydrogen bonds 1.2 The octet rule 1.3 Formal charge 1.4 Sigma (σ) and pi (π) bonds 1.5 Hybridisation 1.6 Inductive effects, hyperconjugation and mesomeric effects 1.6.1 Inductive effects 1.6.2 Hyperconjugation 1.6.3 Mesomeric effects 1.7 Acidity and basicity 1.7.1 Acids 1.7.2 Bases 1.7.3 Lewis acids and bases 1.7.4 Basicity and hybridisation 1.7.5 Acidity and aromaticity 1.7.6 Acid–base reactions Problems
2. Functional Groups, Nomenclature and Drawing Organic Compounds 2.1 Functional groups 2.2 Alkyl and aryl groups 2.3 Alkyl substitution 2.4 Naming carbon chains 2.5 Drawing organic structures Problems
3. Stereochemistry 3.1 Isomerism 3.2 Conformational isomers 3.2.1 Conformations of ethane (CH3CH3) 3.2.2 Conformations of butane (CH3CH2CH2CH3) 3.2.3 Conformations of cycloalkanes 3.2.4 Cyclohexane 3.3 Configurational isomers 3.3.1 Alkenes 3.3.1.1Cisandtransisomerism 3.3.1.2EandZnomenclature
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1 1 2 2 3 4
7 7 7 8 10 10 12 15 15 16 16 17
18 18 19 20 20 23 24
25 25 26 26 27 27 28 30 30 30 31
iv
3.3.2
Problems
Contents
Optical isomers 3.3.2.1 Enantiomers 3.3.2.2 The Cahn–Ingold–Prelog (RandS) nomenclature 3.3.2.3 TheDandLnomenclature 3.3.2.4 Diastereoisomers (or diastereomers) 3.3.2.5 Diastereoisomers versus enantiomers 3.3.2.6 Fischer projections
4. Reactivity and Mechanism 4.1 Reactive intermediates: ions versus radicals 4.2 Nucleophiles and electrophiles 4.2.1 Relative strength 4.2.1.1 Nucleophiles 4.2.1.2 Electrophiles 4.3 Carbocations, carbanions and carbon radicals 4.3.1 Order of stability 4.4 Steric effects 4.5 Oxidation levels 4.6 General types of reaction 4.6.1 Polar reactions (involving ionic intermediates) 4.6.1.1 Addition reactions 4.6.1.2 Elimination reactions 4.6.1.3 Substitution reactions 4.6.1.4 Rearrangement reactions 4.6.2 Radical reactions 4.6.3 Pericyclic reactions 4.7 Ions versus radicals 4.8 Reaction selectivity 4.9 Reaction thermodynamics and kinetics 4.9.1 Thermodynamics 4.9.1.1 Equilibria 4.9.1.2 Enthalpy and entropy 4.9.2 Kinetics 4.9.2.1 Reaction rate 4.9.3 Kinetic versus thermodynamic control 4.10 Orbital overlap and energy 4.11 Guidelines for drawing reaction mechanisms Problems
5. Alkyl Halides 5.1 Structure 5.2 Preparation 5.2.1 Halogenation of alkanes 5.2.2 Halogenation of alcohols 5.2.3 Halogenation of alkenes 5.3 Reactions 5.3.1 Nucleophilic substitution
32 32
33 34 35 35 36 37
40 40 41 42 42 43 44 45 46 46 47
47 47 48 48 49 49 50 51 51 52 52 52 53 54 54 56 57 58 60
62 62 62 62 63 66 67 67
5.3.2
5.3.3 Problems
Contents
5.3.1.1 The SN2 (substitution, nucleophilic, bimolecular) reaction 5.3.1.2 The SN1 (substitution, nucleophilic, unimolecular) reaction 5.3.1.3 SN2 reactions versus SN1 reactions 5.3.1.4 The leaving group 5.3.1.5 Nucleophilic catalysis 5.3.1.6 Tight ion pairs 5.3.1.7 The SNireaction (substitution, nucleophilic, internal reaction) 5.3.1.8 Neighbouring group participation (or anchimeric assistance) 5.3.1.9 The SN2and SN1reactions Elimination 5.3.2.1 The E2 (elimination, bimolecular) reaction 5.3.2.2 The E1 (elimination, unimolecular) reaction 5.3.2.3 E2 reactions versus E1 reactions 5.3.2.4 The E1cB (elimination, unimolecular, conjugate base) reaction Substitution versus elimination
6. Alkenes and Alkynes 6.1 Structure 6.2 Alkenes 6.2.1 Preparation 6.2.2 Reactions 6.2.2.1 Addition of hydrogen halides 6.2.2.2 Addition of bromine 6.2.2.3 Addition of bromine in the presence of water 6.2.2.4 Addition of water (hydration): Markovnikov addition 6.2.2.5 Addition of water (hydration): antiMarkovnikov addition 6.2.2.6 Oxidation by peroxycarboxylic acids (RCO3H) and hydrolysis of epoxides to giveanti dihydroxylation 6.2.2.7Syn dihydroxylation and oxidative
cleavage of 1,2diols to form carbonyls
6.2.2.8 Oxidative cleavage by reaction with ozone (O3) 6.2.2.9 Reaction with carbenes 6.2.2.10 Addition of hydrogen (reduction) 6.2.2.11 Reaction with dienes 6.3 Alkynes 6.3.1 Preparation 6.3.2 Reactions
v
67
68 69 70 70 71
71
72 72 73
73
75 76
77 78 79
81 81 82 82 83 84 86
87
88
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93 94 95 95 96 96 96
vi
Problems
6.3.2.1 6.3.2.2
6.3.2.3
6.3.2.4 6.3.2.5
Contents
Addition of hydrogen halides (HX) Addition of water (hydration): Markovnikov addition Addition of water (hydration): antiMarkovnikov addition Addition of hydrogen (reduction) Deprotonation: formation of alkynyl anions
7. Benzenes 7.1 Structure 7.2 Reactions 7.2.1 Halogenation 7.2.2 Nitration 7.2.3 Sulfonation 7.2.4 Alkylation: the Friedel–Crafts alkylation 7.2.5 Acylation: the Friedel–Crafts acylation 7.3 Reactivity of substituted benzenes 7.3.1 Reactivity of benzene rings: activating and deactivating substituents 7.3.2 Orientation of reactions 7.3.2.1Ortho/paradirecting activators 7.3.2.2Ortho/paradirecting deactivators 7.3.2.3Metadirecting deactivators 7.3.2.4 Steric effects versus electronic effects 7.4 Nucleophilic aromatic substitution (the SNAr mechanism) 7.5 The formation of benzyne 7.6 Transformation of side chains 7.7 Reduction of the benzene ring 7.8 The synthesis of substituted benzenes 7.9 Electrophilic substitution of naphthalene 7.10 Electrophilic substitution of pyridine 7.11 Electrophilic substitution of pyrrole, furan and thiophene Problems
8. Carbonyl Compounds: Aldehydes and Ketones 8.1 Structure 8.2 Reactivity 8.3 Nucleophilic addition reactions 8.3.1 Relative reactivity of aldehydes and ketones 8.3.2 Types of nucleophiles 8.3.3 Nucleophilic addition of hydride: reduction 8.3.3.1 Complex metal hydrides 8.3.3.2 The Meerwein–Ponndorf–Verley reaction
97
97
98 98
99 99
101 101 102 103 103 104 105 106 106
107 108 108 109 109 110
110 111 112 114 115
118 118
118 119
121 121 121 123 123 123 124 124
124
8.4 8.5
8.3.4 8.3.5 8.3.6 8.3.7
Contents
8.3.3.3 The Cannizzaro reaction 8.3.3.4 Nicotinamide adenine dinucleotide (NADH) 8.3.3.5 The reverse of hydride addition: oxidation of alcohols Nucleophilic addition of carbon nucleophiles: formation of CC bonds 8.3.4.1 Reaction with cyanide 8.3.4.2 Reaction with organometallics 8.3.4.3 Reaction with phosphorus ylides: the Wittig reaction Nucleophilic addition of oxygen nucleophiles: formation of hydrates and acetals 8.3.5.1 Addition of water: hydration 8.3.5.2 Addition of alcohols: hemiacetal and acetal formation Nucleophilic addition of sulfur nucleophiles: formation of thioacetals Nucleophilic addition of amine nucleophiles: formation of imines and enamines 8.3.7.1 Formation of imines 8.3.7.2 Reactions of imines, oximes and hydrazones 8.3.7.3 Formation of enamines αSubstitution reactions Keto–enol tautomerism Reactivity of enols 8.4.2.1αHalogenation of aldehydes and ketones Acidity ofαhydrogen atoms: enolate formation Reactivity of enolates 8.4.4.1 Halogenation of enolates 8.4.4.2 Alkylation of enolate ions Carbonyl–carbonyl condensation reactions Condensations of aldehydes and ketones: the aldol reaction Crossed or mixed aldol reactions Intramolecular aldol reactions The Michael reaction
8.4.1 8.4.2 8.4.3 8.4.4
8.5.1 8.5.2 8.5.3 8.5.4 Problems
9. Carbonyl Compounds: Carboxylic Acids and Derivatives 9.1 Structure 9.2 Reactivity 9.3 Nucleophilic acyl substitution reactions 9.3.1 Relative reactivity of carboxylic acid derivatives
vii
125
125
125
126 126 127
128
129 129
130
131
131 131
132 134 134 134 135
136
136 136 137 137 138
138 139 140 140 141
143 143 143 144
144
viii
Contents
9.3.2 Reactivity of carboxylic acid derivatives versus carboxylic acids 9.3.3 Reactivity of carboxylic acid derivatives versus aldehydes/ ketones Nucleophilic substitution reactions of carboxylic acids 9.4.1 Preparation of acid chlorides 9.4.2 Preparation of esters (esterification) Nucleophilic substitution reactions of acid chlorides Nucleophilic substitution reactions of acid anhydrides Nucleophilic substitution reactions of esters Nucleophilic substitution and reduction reactions of amides Nucleophilic addition reactions of nitriles αSubstitution reactions of carboxylic acids Carbonyl–carbonyl condensation reactions 9.11.1 The Claisen condensation reaction 9.11.2 Crossed or mixed Claisen condensations 9.11.3 Intramolecular Claisen condensations: the Dieckmann reaction A summary of carbonyl reactivity Problems
9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 9.12
10. Spectroscopy 10.1 Mass spectrometry 10.1.1 Introduction 10.1.2 Isotope patterns 10.1.3 Determination of molecular formula 10.1.4 Fragmentation patterns 10.1.5 Chemical ionisation 10.2 The electromagnetic spectrum 10.3 Ultraviolet spectroscopy 10.4 Infrared spectroscopy 10.5 Nuclear magnetic resonance spectroscopy 1 10.5.1 H NMR spectroscopy 10.5.1.1 Chemical shifts 10.5.1.2 Spin–spin splitting or coupling 10.5.1.3 Summary 13 10.5.2 C NMR spectroscopy Problems
11. Natural Products and Synthetic Polymers 11.1 Carbohydrates 11.2 Lipids
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145 145 146
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148 149
150 151 153 153 153
154
155 156 156
159 159 159 160
161 162 163 163 164 165 167 170 170 171 173 174 175
177 177 179
Contents
11.2.1 Waxes, fats and oils 11.2.2 Steroids 11.3 Amino acids, peptides and proteins 11.4 Nucleic acids 11.5 Synthetic polymers 11.5.1 Addition polymers 11.5.2 Condensation polymers Problems
Outline Answers Further Reading Appendix 1 Bond Dissociation Energies Appendix 2 Bond Lengths Appendix 3 Approximate pKaValues (Relative to Water) Appendix 4 Useful Abbreviations Appendix 5 Infrared Absorptions 1 Appendix 6 Approximate H NMR Chemical Shifts Index
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179 180 180 183 184 184 186 187
189208 209210211212213214216