Arrow Pushing in Inorganic Chemistry A Logical Approach to the Chemistry of the Main-Group Elements

Steffen Berg and Abhik Ghosh are chemists based at UiT – The Arctic University of Norway. They share a passion for chemical education, and are particularly interested in developing methods to help high school students and undergraduates understand difficult concepts.

PREFACE xiii

ACKNOWLEDGMENTS xvii

1. A Collection of Basic Concepts 1

1.1 Nucleophiles and Electrophiles: The SN2 Paradigm 2

1.2 What Makes for a Good Nucleophile? 5

1.3 Hard and Soft Acids and Bases: The HSAB Principle 8

1.4 pKa Values: What Makes for a Good Leaving Group? 9

1.5 Redox Potentials 11

1.6 Thermodynamic Control: Bond Dissociation Energies (BDEs) 11

1.7 Bimolecular -Elimination (E2) 14

1.8 Proton Transfers (PTs) 15

1.9 Elementary Associative and Dissociative Processes (A and D) 16

1.10 Two-Step Ionic Mechanisms: The SN2-Si Pathway 19

1.11 Two-Step Ionic Mechanisms: The SN1 and E1 Pathways 20

1.12 Electrophilic Addition to Carbon–Carbon Multiple Bonds 22

1.13 Electrophilic Substitution on Aromatics: Addition–Elimination 23

1.14 Nucleophilic Addition to Carbon–Heteroatom Multiple Bonds 24

1.15 Carbanions and Related Synthetic Intermediates 26

1.16 Carbenes 29

1.17 Oxidative Additions and Reductive Eliminations 30

1.18 Migrations 32

1.19 Ligand Exchange Reactions 33

1.20 Radical Reactions 35

1.21 Pericyclic Reactions 37

1.22 Arrow Pushing: Organic Paradigms 38

1.23 Inorganic Arrow Pushing: Thinking Like a Lone Pair 38

1.24 Definitions: Valence, Oxidation State, Formal Charge, and Coordination Number 40

1.25 Elements of Bonding in Hypervalent Compounds 41

1.26 The Convention 45

1.27 The Inert Pair Effect 46

1.28 Summary 47

Further Reading 48

2. The s-Block Elements: Alkali and Alkaline Earth Metals 50

2.1 Solubility 51

2.2 The s-Block Metals as Reducing Agents 52

2.3 Reductive Couplings 53

2.4 Dissolving Metal Reactions 56

2.5 Organolithium and Organomagnesium Compounds 58

2.6 Dihydrogen Activation by Frustrated Lewis Pairs (FLPs) 61

2.7 A MgI–MgI Bond 63

2.8 Summary 64

Further Reading 65

3. Group 13 Elements 66

3.1 Group 13 Compounds as Lewis Acids 67

3.2 Hydroboration 70

3.3 Group 13-Based Reducing Agents 73

3.4 From Borazine to Gallium Arsenide: 13–15 Compounds 76

3.5 Low-Oxidation-State Compounds 80

3.6 The Boryl Anion 87

3.7 Indium-Mediated Allylations 88

3.8 Thallium Reagents 89

3.9 Summary 94

Further Reading 94

4. Group 14 Elements 96

4.1 Silyl Protecting Groups 98

4.2 A Case Study: Peterson Olefination 103

4.3 Silanes 104

4.4 The -Silicon Effect: Allylsilanes 106

4.5 Silyl Anions 109

4.6 Organostannanes 112

4.7 Polystannanes 113

4.8∗ Carbene and Alkene Analogs 115

4.9∗ Alkyne Analogs 120

4.10 Silyl Cations 122

4.11 Glycol Cleavage by Lead Tetraacetate 124

4.12 Summary 127

Further Reading 128

5A. Nitrogen 129

5A.1 Ammonia and Some Other Common Nitrogen Nucleophiles 130

5A.2 Some Common Nitrogen Electrophiles: Oxides, Oxoacids, and Oxoanions 131

5A.3 N–N Bonded Molecules: Synthesis of Hydrazine 133

5A.4 Multiple Bond Formation: Synthesis of Sodium Azide 135

5A.5 Thermal Decomposition of NH4NO2 and NH4NO3 137

5A.6 Diazonium Salts 138

5A.7 Azo Compounds and Diazene 140

5A.8∗ Imines and Related Functional Groups: The Wolff–Kishner Reduction and the Shapiro Reaction 144

5A.9 Diazo Compounds 146

5A.10 Nitrenes and Nitrenoids: The Curtius Rearrangement 149

5A.11 Nitric Oxide and Nitrogen Dioxide 151

5A.12 Summary 155

Further Reading 155

5B. The Heavier Pnictogens 156

5B.1 Oxides 158

5B.2 Halides and Oxohalides 160

5B.3 Phosphorus in Biology: Why Nature Chose Phosphate 163

5B.4 Arsenic-Based DNA 166

5B.5 Arsenic Toxicity and Biomethylation 168

5B.6 Alkali-Induced Disproportionation of Phosphorus 171

5B.7 Disproportionation of Hypophosphorous Acid 173

5B.8 The Arbuzov Reaction 175

5B.9 The Wittig and Related Reactions: Phosphorus Ylides 176

5B.10 Phosphazenes 180

5B.11∗ The Corey–Winter Olefination 185

5B.12 Triphenylphosphine-Mediated Halogenations 187

5B.13∗ The Mitsunobu Reaction 188

5B.14∗ The Vilsmeier–Haack Reaction 191

5B.15 SbF5 and Superacids 193

5B.16 Bismuth in Organic Synthesis: Green Chemistry 195

5B.17 Summary 200

Further Reading 200

6. Group 16 Elements: The Chalcogens 202

6.1 The Divalent State: Focus on Sulfur 204

6.2 The Divalent State: Hydrogen Peroxide 205

6.3 S2Cl2 and SCl2 209

6.4 Nucleophilic Breakdown of Cyclopolysulfur Rings 211

6.5 Cyclooctachalcogen Ring Formation 213

6.6 Higher-Valent States: Oxides and Oxoacids 215

6.7 Sulfur Oxochlorides 219

6.8 Ozone 222

6.9 Swern and Related Oxidations 226

6.10 Sulfur Ylides and Sulfur-Stabilized Carbanions 228

6.11∗ Hydrolysis of S2F2: A Mechanistic Puzzle 231

6.12 Higher-Valent Sulfur Fluorides 234

6.13 Martin Sulfurane 236

6.14 Lawesson’s Reagent 238

6.15 Sulfur Nitrides 240

6.16∗ Selenium-Mediated Oxidations 243

6.17 Higher-Valent Tellurium: A Mechanistic Puzzle 247

6.18 Summary 250

Further Reading 251

7. The Halogens 252

7.1 Some Notes on Elemental Halogens 254

7.2 Alkali-Induced Disproportionation of Molecular Halogens 258

7.3 Acid-Induced Comproportionation of Halate and Halide 260

7.4 Hypofluorous Acid, HOF 261

7.5 Electrophilic Fluorinating Agents: N-Fluoro Compounds 264

7.6 Oxoacids and Oxoanions 268

7.7 Heptavalent Chlorine 271

7.8 Interhalogen Compounds 275

7.9∗ Halogens in Organic Synthesis: Some Classical Reactions 276

7.10 An Introduction to Higher-Valent Organoiodine Compounds 283

7.11 3-Iodanes 284

7.12 5-Iodanes: IBX and Dess–Martin Periodinane 288

7.13 Periodic Acid Oxidations 290

7.14 Bromine Trifluoride 291

7.15∗ Aryl-3-Bromanes 294

7.16 Summary 298

Further Reading 299

8. The Noble Gases 300

8.1 The Xenon Fluorides: Fluoride Donors and Acceptors 302

8.2 O/F Ligand Exchanges 303

8.3 Xenon Fluorides as F+ Donors and Oxidants 304

8.4 Hydrolysis of XeF2 and XeF4 306

8.5 Xenate and Perxenate 307

8.6 Disproportionation of Xenate 308

8.7 Hydrolysis of XeF4 310

8.8 Other Compounds Containing Xe–O Bonds 311

8.9 Xe–N Bonds 312

8.10 Xe–C Bonds 313

8.11 Krypton Difluoride 314

8.12 Plus Ultra 316

8.13 Summary 316

Further Reading 316

Epilogue 318

Appendix A. Inorganic Chemistry Textbooks, with a Descriptive-Inorganic Focus 319

A.1 Introductory Texts 319

A.2 Advanced Texts 319

Appendix B. A Short List of Advanced Organic Chemistry Textbooks 320

Index 321

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