Eusebio Juaristi, PhD, is Professor at Centro de Investigacion de Estudios Avanzados del Instituto Politecnico Nacional, Mexico City, [...] has produced influential research in numerous areas of physical organic chemistry, particularly conformational analysis and stereochemistry, as well as computational chemistry, asymmetric organocatalysis, and sustainable chemistry.

C. Gabriela Ávila-Ortiz, PhD, is a Research Assistant at Centro de Investigacion de Estudios Avanzados del Instituto Politecnico Nacional, Mexico City, Mexico. She works in Professor Juaristi's research group studying the asymmetric synthesis of organic compounds, organocatalysis, and green chemistry.

Alberto Vega-Peñaloza, PhD, is Serra Hunter Lecturer in the Section of Organic Chemistry at the University of Barcelona, Spain. He has worked as Senior Scientist I at Selvita S.A., Poland, as a postdoctoral fellow at the Faculty of Chemistry of the National Autonomous University of Mexico (UNAM), as a postdoctoral researcher at ICIQ in Spain, and at the University of Padova, Italy, where he was awarded the Seal of Excellence UniPD grant to work on the development of photocatalytic systems for sustainable synthetic methods.

Preface ix

Chapter 1 Introduction and History of the Molecular Orbital Theory 1

Introduction 1

Nature of Electromagnetic Radiation 2

The Wave Nature of Light 3

Electromagnetic Spectrum 5

The Distinction Between Energy and Matter 6

The Particle Nature of Light 7

Mass and Momentum Associated with a Light Quantum 11

Wave-Particle Duality 13

Application of Quantum Mechanics to Atomic Structure 14

Schrödinger's Equation 19

Hydrogenic Orbitals 23

Why Doesn't the Electron Fall into the Nucleus? Bohr's Legacy and the Quantum Mechanical Model 32

Further Reading 33

Exercises 34

Chapter 2 Hybrid Orbitals 35

Introduction 35

Hybridisation Theory 37

Wavefunctions Associated with Hybrid Orbitals 42

Procedure to Build a Hybrid Orbital 43

Orthogonality of Wave Functions (Orbitals) 44

The Bent Bond or Tau Model 45

Effects of Hybridisation 45

Further Reading 51

Exercises 51

Chapter 3 Bond Formation from Atomic Orbitals 53

Introduction 53

Mixing of s Orbitals 53

Mixing of p Orbitals 58

Factors Affecting the Magnitude of Orbital Interactions 60

Bonding in Homo-Diatomic Molecules 62

Bonding in Hetero-Diatomic Molecules 68

Bonding in Triatomic Molecules 72

Conjugated Systems 84

Further Reading 84

Exercises 84

Chapter 4 The Hückel Molecular Orbital Method (HMO) 85

The Linear Combination of Atomic Orbitals (LCAO) Method 85

The Hückel Molecular Orbital (HMO) Method 86

Simplified Procedure for the Application of Hückel¿s Method 91

Application of Hückel¿s Method: Several Examples 92

Application to Larger Molecules 96

Scope and Limitations of the Hückel Molecular Orbital Method 97

Hückel Molecular Orbital Method in Cyclic ¿¿¿-Systems 97

Energy Diagrams for Acyclic Polyenes 101

¿¿¿-Systems Containing Heteroatoms 102

Inclusion of Overlap Between Vicinal Atoms 106

The Shape of the Molecular Orbitals 108

Contribution of the AOs in a Molecular Orbital 108

Symmetry Simplifications in Alternant Hydrocarbons 112

Estimation of MO Energies and Coefficients 115

Bond Orders ¿(¿P¿ ij )¿ 116

Charge Distribution (¿q¿ I ) 118

Index of Free Valence (¿f¿ I ) 119

Further Reading 120

Exercises 121

Chapter 5 Interactions Between Molecular Orbitals: Chemical Reactions 123

Introduction 123

Molecular Orbital Theory of Selected Organic Reactions 127

Summary 140

Further Reading 141

Exercises 141

Chapter 6 Some Applications of Orbital Theory in Organic

Chemistry 143

Introduction 143

Ultraviolet Spectroscopy 143

Ionisation Potentials 146

Photoelectron Spectroscopy (PES) 147

Interactions Between ¿¿¿ Orbitals 148

Interactions Between n-Orbitals 151

Electron Spectroscopy for Chemical Analysis (ESCA) Spectroscopy 155

Charge Transfer Complexes (EDA Complexes) 155

Further Reading 156

Exercises 157

Chapter 7 Conservation of Molecular Orbital

Symmetry: Introduction to Pericyclic

Reactions - Cycloaddition Reactions 159

Introduction 159

Concerted Reactions 160

Pericyclic Reactions 161

Principles of the Conservation of Orbital Symmetry 164

Symmetry Correlation Diagrams of Molecular Orbitals 164

Analysis of the Symmetry of the HOMO/LUMO Frontier Orbitals (FMO) 168

Analysis of the Nodal Properties at the Transition State of a Cyclisation Reaction 169

Cycloaddition Reactions 172

1,3-Butadiene + Ethylene ¿¿¿ Cyclohexene 173

Two Ethylene Molecules ¿¿¿ Cyclobutane 175

Supra- or Antarafacial Topicity in Cycloaddition Reactions 179

Effect of Secondary Interactions Between Molecular Orbitals 180

Further Reading 182

Exercises 182

Chapter 8 Cheletropic Reactions 185

Introduction 185

[2 + 2] Cheletropic Reactions 186

[4 + 2] Cheletropic Reactions 190

[6 + 2] Cheletropic Reactions 194

Further Reading 196

Exercises 196

Chapter 9 Electrocyclic Reactions 199

Introduction 199

1,3-Butadiene ¿¿¿ Cyclobutene 201

1,3,5-Hexatriene ¿¿¿ 1,3-Cyclohexadiene 204

Photochemical Electrocyclic Reactions 207

Further Reading 210

Exercises 210

Chapter 10 Sigmatropic Reactions 213

Introduction 213

[3,3] Sigmatropic Rearrangements 216

[1,3] Sigmatropic Rearrangements of Alkyl Groups 218

Analysis of Nodal Properties in the Transition State 221

[1,5] Sigmatropic Rearrangements of Alkyl Groups 221

[1,2] Sigmatropic Rearrangements of Alkyl Groups 225

[1,3] Sigmatropic Rearrangements of Hydrogen 227

[1,5] Sigmatropic Rearrangements of Hydrogen 228

Further Reading 231

Exercises 232

Chapter 11 1,3-Dipolar Cycloadditions 235

Introduction 235

Classification of 1,3-Dipolar Reactants 235

Frontier Molecular Orbital Analysis 236

Analysis of Nodal Properties in the Transition State 238

Types of 1,3-DPCA Reactions and Regioselectivity 239

1,3-DPCA Reactions with Diazoalkanes 242

1,3-DPCA Reactions with Nitrones 243

1,3-DPCA Reactions with Azomethine Ylides as the

1,3-Dipolar Reactant 245

1,3-DPCA Reactions with Nitrile Oxides as 1,3-Dipolar Reactants 247

1,3-DPCA Reactions with Azides, Osmium Tetroxide and

Ozone 248

Further Reading 251

Exercises 251

Chapter 12 Stereoelectronic Interactions 255

Introduction 255

Interpretation of the anomeric effect 258

Stereoelectronic interactions in S-C-P segments 261

Further Reading 266

Exercises 267

Index 269