Molecular Orbitals and Organic Chemical Reactions

Winner of the PROSE Award for Chemistry & Physics 2010

Acknowledging the very best in professional and scholarly publishing, the annual PROSE Awards recognise publishers' and authors' commitment to pioneering works of research and for contributing to the conception, production, and design of landmark works in their fields. Judged by peer publishers, librarians, and medical professionals, Wiley are pleased to congratulate Professor Ian Fleming, winner of the PROSE Award in Chemistry and Physics for Molecular Orbitals and Organic Chemical Reactions.

Molecular orbital theory is used by chemists to describe the arrangement of electrons in chemical structures. It is also a theory capable of giving some insight into the forces involved in the making and breaking of chemical bonds—the chemical reactions that are often the focus of an organic chemist's interest. Organic chemists with a serious interest in understanding and explaining their work usually express their ideas in molecular orbital terms, so much so that it is now an essential component of every organic chemist's skills to have some acquaintance with molecular orbital theory.

Molecular Orbitals and Organic Chemical Reactions is both a simplified account of molecular orbital theory and a review of its applications in organic chemistry; it provides a basic introduction to the subject and a wealth of illustrative examples. In this book molecular orbital theory is presented in a much simplified, and entirely non-mathematical language, accessible to every organic chemist, whether student or research worker, whether mathematically competent or not. Topics covered include:

• Molecular Orbital Theory
• Molecular Orbitals and the Structures of Organic Molecules
• Chemical Reactions — How Far and How Fast
• Ionic Reactions — Reactivity
• Ionic Reactions — Stereochemistry
• Pericyclic Reactions
• Radical Reactions
• Photochemical Reactions

Slides for lectures and presentations are available on the supplementary website: www.wiley.com/go/fleming_student

Molecular Orbitals and Organic Chemical Reactions: Student Edition is an invaluable first textbook on this important subject for students of organic, physical organic and computational chemistry.

The Reference Edition edition takes the content and the same non-mathematical approach of the Student Edition, and adds extensive extra subject coverage, detail and over 1500 references. The additional material adds a deeper understanding of the models used, and includes a broader range of applications and case studies. Providing a complete in-depth reference for a more advanced audience, this edition will find a place on the bookshelves of researchers and advanced students of organic, physical organic and computational chemistry. Further information can be viewed here.

"These books are the result of years of work, which began as an attempt to write a second edition of my 1976 book Frontier Orbitals and Organic Chemical Reactions. I wanted to give a rather more thorough introduction to molecular orbitals, while maintaining my focus on the organic chemist who did not want a mathematical account, but still wanted to understand organic chemistry at a physical level. I'm delighted to win this prize, and hope a new generation of chemists will benefit from these books."
-Professor Ian Fleming

Preface xi

1 Molecular Orbital Theory 1

1.1 The Atomic Orbitals of a Hydrogen Atom 1

1.2 Molecules made from Hydrogen Atoms 2

1.3 C—H and C—C Bonds 9

1.4 Conjugation—Hückel Theory 22

1.5 Aromaticity 32

1.6 Strained Bonds—Cyclopropanes and Cyclobutanes 39

1.7 Heteronuclear Bonds, C—M, C—X and C=O 42

1.8 The Tau Bond Model 52

1.9 Spectroscopic Methods 53

1.10 Exercises 57

2 The Structures of Organic Molecules 59

2.1 The Effects of Conjugation 59

2.2 Conjugation—Hyperconjugation 69

2.3 The Configurations and Conformations of Molecules 81

2.4 Other Noncovalent Interactions 90

2.5 Exercises 95

3 Chemical Reactions—How Far and How Fast 97

3.1 Factors Affecting the Position of an Equilibrium 97

3.2 The Principle of Hard and Soft Acids and Bases (hsab) 97

3.3 Transition Structures 103

3.4 The Perturbation Theory of Reactivity 104

3.5 The Salem-Klopman Equation 106

3.6 Hard and Soft Nucleophiles and Electrophiles 109

3.7 Other Factors Affecting Chemical Reactivity 110

4 Ionic Reactions—Reactivity 111

4.1 Single Electron Transfer (SET) in Ionic Reactions 111

4.2 Nucleophilicity 114

4.3 Ambident Nucleophiles 121

4.4 Electrophilicity 134

4.5 Ambident Electrophiles 137

4.6 Carbenes 147

4.7 Exercises 151

5 Ionic Reactions—Stereochemistry 153

5.1 The Stereochemistry of the Fundamental Organic Reactions 154

5.2 Diastereoselectivity 167

5.3 Exercises 183

6 Thermal Pericyclic Reactions 185

6.1 The Four Classes of Pericyclic Reactions 186

6.2 Evidence for the Concertedness of Bond Making and Breaking 188

6.3 Symmetry-Allowed and Symmetry-Forbidden Reactions 190

6.4 Explanations for the Woodward-Hoffmann Rules 214

6.5 Secondary Effects 221

6.6 Exercises 270

7 Radical Reactions 275

7.1 Nucleophilic and Electrophilic Radicals 275

7.2 The Abstraction of Hydrogen and Halogen Atoms 277

7.3 The Addition of Radicals to Bonds 279

7.4 Synthetic Applications of the Chemoselectivity of Radicals 286

7.5 Stereochemistry in some Radical Reactions 287

7.6 Ambident Radicals 290

7.7 Radical Coupling 295

7.8 Exercises 296

8 Photochemical Reactions 299

8.1 Photochemical Reactions in General 299

8.2 Photochemical Ionic Reactions 301

8.3 Photochemical Pericyclic Reactions and Related Stepwise Reactions 304

8.4 Photochemically Induced Radical Reactions 321

8.5 Chemiluminescence 323

8.6 Exercises 324

References 327

Index 331

"Fleming uses nonquantitative molecular orbital theory to explain many common phenomena in organic chemistry. As such, this is a very powerful tool for students of advanced organic chemistry. Much of what is taken simply on faith or with some hand waving in sophomore organic chemistry can be readily explained with molecular orbital theory, which is usually considered too advanced for students at that level. Though this book could be used as the primary textbook for a course solely on molecular orbitals in organic chemistry, it will more likely be used as a reference source for an advanced organic chemistry course for upper-level undergraduates or graduate students." (CHOICE, August 2010)

"The new 'Fleming' is a must for every lecturer and every student of chemistry—a fantastic book. In this new form the textbook will last for another 30 years and remain as fresh as did its predecessor!" (Angewandte Chemie International Edition March 2010)

Professor Ian Fleming, Department of Chemistry, University of Cambridge
Ian Fleming is an Emeritus Professor in the Department of Chemistry in the University of Cambridge, and an Emeritus Fellow of Pembroke College. He is the author of five textbooks: Spectroscopic Methods in Organic Chemistry (McGraw Hill, now in its 6th edition), Spectroscopic Problems in Organic Chemistry (McGraw Hill); Selected Organic Syntheses (Wiley), Frontier Orbitals and Organic Chemical Reactions (Wiley) and Pericyclic Reactions (OUP Oxford Chemistry Primer series). Molecular orbital theory I used by chemists to describe the arrangement of electrons in chemical structures. It is also a theory capable of giving some insight into the forces involved in the making and breaking of chemical bonds – the chemical reactions that are often the focus of an organic and breaking of chemical bonds – the chemical reactions that are often the focus of an organic chemist’s interest. Organic chemists with a serious interest in understanding and explaining their work usually express their ideas in molecular orbital terms, so much so that it is now an essential component or every organic chemist’s stills to have some acquaintance with molecular orbital theory.

Molecular Orbitals and Organic Chemical Reactions is both a simplified account of molecular orbital theory and a review of it applications in organic chemistry; it provides a basic introduction to the subject and a wealth of illustrative examples. In this book molecular orbital theory is presented in a much simplified, and entirely non-mathematical language, accessible to every organic chemist, whether student or research worker, whether mathematically competent or not. Topics covered include:

• Molecular Orbital Theory
• Molecular Orbitals and the Structures of Organic Molecules
• Chemical Reactions – How Far and How Fast
• Ionic Reactions – Reactivity
• Ionic Reactions – Stereochemistry
• Pericyclic Reactions
• Radical Reactions
• Photochemical Reactions

Molecular Orbitals and Organic Chemical Reactions: Student Edition serves in a sense as a second edition of the author’s influential earlier book Frontier Orbitals and Organic Chemical Reactions, but has been completely rewritten, greatly enlarging the chapters on molecular orbital theory itself, and on the theoretical basis for the principle of hard and soft acids and bases, and a whole chapter on the stereochemistry of the fundamental organic reactions. Correlation diagrams have been added to the discussion of pericyclic chemistry, and a great deal more in that, the largest chapter. A number of new topics, both omissions from the earlier book and work that has taken place in the intervening years, are included, and there are more words of caution in discussing frontier orbital theory itself.

Molecular Orbitals and Organic Chemical Reactions: Student Edition is an individual textbook on this important subject for student or organic, physical organic and computational chemistry.