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Advanced Organic Chemistry: Part A: Structure and Mechanisms PDF

600 Pages·1995·15.441 MB·English
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Advanced Organic Chemistry Part A: Structure and Mechanisms ADVANCED ORGANIC CHEMISTRY PART A: Structure and Mechanisms PART B: Reactions and Synthesis Advanced Organic Chemistry Part A: Structure and Mechanisms Francis A. Carey and Richard 1. Sundberg University of Virginia, Charlottesville, Virginia PLENUM PRESS • NEW YORK AND LONDON Library of Congress Cataloging in Publication Data Carey, Francis A 1937- Advanced organic chemistry. Includes bibliographical references and indexes. CONTENTS: pt. A. Structure and mechanisms.-pt. B. Reactions and synthesis. 1. Chemistry, Organic. I. Sundberg, Richard J., 1938- joint author. II. Title. [DNLM: 1. Chemistry, Organic. QD258 C273a) QD251.2.C36 547 76-26090 ISBN-13: 978-1-4615-8884-9 e-ISBN-13: 978-1-4615-8882-5 001: 10.1007/978-1-4615-8882-5 Softcover reprint of the hardcover 1s t edition 1977 © 1977 Plenum Press, New York A Division of Plenum Publishing Corporation 227 West 17th Street, New York, N.Y. 10011 All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher Preface to Part A This volume is intended to serve as an advanced text in organic chemistry and is aimed at developing a deeper understanding of the structure of organic compounds and the mechanisms of organic reactions. The text assumes introductory courses in organic chemistry and in physical chemistry. The first three chapters consider three fundamental aspects of the structure of organic molecules: bondirfg, stereochemis try, and conformation. Chapter 4 is an overview of the methods that have been used to probe details of organic reaction mechanisms. The remaining chapters are organized on the basis of fundamental mechanistic patterns, although we return to the topic of structure in Chapter 9, in which aromatic molecules are considered. At Virginia, we have used this material in a course that serves third- and fourth-year undergraduate chemistry majors and beginning graduate students. By the use of extensive references and referenced problems from the literature, we hope to provide an opportunity for the student to delve into the research literature. Considerable numerical data are included with the intent that the student can supplement a qualitative understanding of the role that substituents and other structural features play in organic reactions with some grasp of the magnitude of such effects. A considerable amount of this material is presented with a minimum of commentary in schemes and tables. Much of organic chemistry, however, resists interpretation in terms of a single variable. Often, several factors may operate in different directions to influence rate or equilibria or both, and it may not be possible to make consistently correct interpretations by inspection. Caution also needs to be exercised in attempts at rationalizing small differences in rate or equilibria or both. We recommend that instructors and students use these schemes and tables as working outlines for further discussion. We have tried to emphasize the teaching of concepts in our development and treatment of the material. This emphasis of concepts is often best done by referring the reader to review articles, and sometimes produces the unfortunate result of failing to credit important contributions to their original source. To our colleagues v VI whose work fell into this category, we extend our apologies and request their understanding of our attempts to produce a working text, rather than to review the PREFACE TO PART A historical development of various concepts and techniques. This volume is a companion to Part B, Reactions and Synthesis. Part B emphasizes the synthetically important organic reactions. It adds some further mechanistic information, but is aimed primarily at introducing to students the available repertoire of organic reactions and providing an opportunity to develop a background in synthetic methodology. We believe that Parts A and B used sequentially as texts in a one-year advanced course will prepare the student to turn to the extensive review and monograph literature and to the primary journals with a thorough exposure to both the mechanistic and synthetic areas of organic chemistry. Francis A. Carey Richard J. Sundberg Charlottesville, Virginia Contents of Part A List of Figures Xlll List of Tables xvii List of Schemes xxi Contents of Part B xxiii Chapter 1. Chemical Bonding and Molecular Structure 1 Introduction . . . . . . . . . . . . . . . 1 1.1. Valence-Bond Approach to Chemical Bonding 2 1.2. Bond Energies, Lengths, and Dipoles 10 1.3. Molecular Orbital Theory 15 1.4. Hiickel Molecular Orbital Theory 26 General References 32 Problems 32 Chapter 2. Stereochemical Principles 39 Introduction . . . . . . . 39 2.1. Enantiomeric Relationships 40 2.2. Diastereomeric Relationships 45 2.3. Dynamic Stereochemistry. 53 2.4. Prochiral Relationships 61 General References 66 Problems .... 66 Chapter 3. Conformational and Other Steric Effects 71 Introduction . . . . . . . . . . . 71 3.1. Steric Strain and Molecular Mechanics 72 3.2. Conformations of Acyclic Molecules . 78 Vlll 3.3. Conformations of Cyclohexane Derivatives . 83 3.4. Carbocyclic Rings Other Than Six-Membered 94 CONTENTS OF PART A 3.5. Heterocyclic Conformational Analysis . . . 98 3.6. Molecular Orbital Methods Applied to Conformational Analysis 103 3.7. Conformational Effects on Reactivity 107 3.8. Other Steric Effects on Reactivity 111 General References 119 Problems .... 119 Chapter 4. Study and Description of Organic Reaction Mechanisms 125 Introduction . . . . 125 4.1. Thermodynamic Data .............. . 125 4.2. Kinetic Data . . . . . . . . . . . . . . . . . . . 127 4.3. Substituent Effects and Linear Free-Energy Relationships 139 4.4. Isotope Effe<;ts . . . . . . . . . . . . 149 4.5. Characterization of Reaction Intermediates 152 4.6. Catalysis ............. . 154 4.7. Solvent Effects . . . . . . . . . . . . 158 4.8. Basic Mechanistic Concepts: Kinetic Versus Thermodynamic Control, Hammond's Postulate, the Curtin-Hammett Principle 163 4.9. Isotopes in Labeling Experiments 170 4.10. Stereochemistry 171 General References 172 Problems .... 173 Chapter 5. Nucleophilic Substitution 183 Introduction . . . . . . . . . . . . . . . . . . . . 183 5.1. The Limiting Cases-Substitution by the Ionization (SN1) Mechanism . . . . . . . . . . . . . . . . . . . . . 184 5.2. The Limiting Cases-Substitution by the Direct Displacement (SN2) Mechanism .......... 187 5.3. Alternative Mechanistic Hypotheses 190 5.4. Carbonium Ions 195 5.5. Nucleophilicity . . . . . . . . . 206 5.6. Leaving-Group Effects ..... 212 5.7. Steric and Other Substituent Effects on Substitution and Ionization Rates . . . . . . . . . . . . . . . . . . . . . . . . 215 5.8. Stereochemistry of Nucleophilic Substitution ....... 219 5.9. Secondary Kinetic Isotope Effects in Substitution Mechanisms 227 5.10. Neighboring-GroupParticipation . . . . . . . . . . . . 229 5.11. Carbonium Ion Rearrangements ............ 236 5.12. Nonclassical Carbonium Ions and the Norbornyl Cation Problem 242 5.13. Synthetic Applications of Nucleophilic Substitution Reactions 249 General References 257 Problems .... 257 Chapter 6. Polar Addition and Elimination Reactions 265 IX Introduction . . . . . . . . . . . . 265 CONTENTS OF PART A 6.1. Addition of Hydrogen Halides to Alkenes 266 6.2. Acid-Catalyzed Hydration of Alkenes 271 6.3. Addition of Halogens . . . . . . . 272 6.4. TheE2,El,andElcbMechanisms .. 278 6.5. Orientation Effects in Elimination Reactions 282 6.6. Stereochemistry of E2 Elimination Reactions 286 6.7. Dehydration of Alcohols . . . . . . 290 6.8. Eliminations Not Involving C-H Bonds 291 General References 294 Problems .... 294 Chapter 7. Carbanions and Other Nucleophilic Carbon Species 299 Introduction . . . . . . . . . . . . . 299 7.1. Acidity of Hydrocarbons . . . . . . . . 299 7.2. Carbanions Stabilized by Functional Groups 307 7.3. Enols and Enamines 315 General References 319 Problems .... 319 Chapter 8. Reactions of Carbonyl Compounds 325 Introduction . . . . . . . . . . . . . . . . . . . . . 325 8.1. Hydration and Addition of Alcohols to Aldehydes and Ketones 326 8.2. Addition-Elimination Reactions of Ketones and Aldehydes 329 8.3. Reactivity of Carbonyl Compounds toward Addition 334 8.4. Ester Hydrolysis and Related Reactions ..... . 335 8.5. Amide Hydrolysis .............. . 341 8.6. Acylation of Nucleophilic Oxygen and Nitrogen Groups 343 8.7. Intramolecular Catalysis 347 General References 352 Problems 352 Chapter 9. Aromaticity and Electrophilic Aromatic Substitution 361 9.1. Aromaticity . . . . . . . . . . 361 9.1.1. The Concept of Aromaticity 361 9.1.2. TheAnnulenes ..... . 365 9.1.3. Aromaticity in Charged Rings 372 9.1.4. Fused-RingSystems 376 9.1.5. Homoaromaticity . . . . . 383 9.2. Electrophilic Aromatic Substitution Reactions 385 9.3. Structure-Reactivity Relationships 391 9.4. Specific Substitution Mechanisms 400 9.4.1. Nitration ...... . 400 x 9.4.2. Halogenation ............. . 404 9.4.3. Protonation and Hydrogen Exchange ... . 408 CONTENTS OF PART A 9.4.4. Friedel-Crafts Alkylation and Related Reactions 410 9.4.5. Friedel-Crafts Acylation and Related Reactions 412 9.4.6. Coupling with Diazonium Compounds . . . . 414 9.4.7. Substitution of Groups Other Than Hydrogen . 415 9.5. Theoretical Treatments of Aromatic Substitution Reactions 417 General References 419 Problems .... 419 Chapter 10. Concerted Reactions 425 Introduction . . . . . . 425 10.1. Electrocyc1ic Reactions 426 10.2. SigmatropicRearrangements 439 10.3. Cyc1oaddition and Cyc1oelimination Reactions 449 General References 457 Problems .... 458 Chapter 11. Photochemistry 465 11.1. General Principles ................. 465 11.2. Orbital Symmetry Considerations Related to Photochemical Reactions . . . . . . . . . . . . 470 11. 3. Photochemistry of Carbonyl Groups . . 474 11.4. Photochemistry of Alkenes and Dienes . 483 11.5. Photochemistry of Aromatic Compounds 492 General References 494 Problems 494 Chapter 12. Free-Radical Reactions 501 12.1. Generation and Characterization of Free Radicals 501 12.1.1. Background ........... . 501 12.1.2. Stable Free Radicals ........ . 502 12.1.3. Direct Detection of Radical Intermediates 504 12.1.4. Sources of Free Radicals ...... . 510 12.1.5. Structural and Stereochemical Properties of Radical Intermediates . . . . . . . . . . . . . . . . 512 12.1.6. ChargedRadicalSpecies .......... . 516 12.2. Characteristics of Reaction Mechanisms Involving Radical Intermediates . . . . . . . . . . . . . . . . 519 12.2.1. Kinetic Characteristics of Chain Reactions 519 12.2.2. Structure-Reactivity Relationships 522 12.3. Free-Radical Substitution Reactions 527 12.3.1. Halogenation 527 12.3.2. Oxidation 531

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