Introduction to Magnetic Resonance Spectroscopy ESR, NMR, NQR, 3ed 9788194778769
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Table of contents :
Cover
Half title
Title
Copyright
Preface to the Third Edition
Preface to the Second Edition
Preface to the First Edition
Acknowledgements
Contents
Chapter 1: General Introduction
Introduction
Electromagnetic Radiation
Number of Spectral Lines
Spectral Line Width
Band Intensities
Spin Transitions
Exercises
Part One: Electron Spin Resonance
Chapter 2: Basic Theory
General Remarks
ESR Transitions
Selection Rules
g–Factor
Presentation of Spectra
Interaction of Magnetic Dipoles with Microwave Radiation
Larmor Precession
Resonance Phenomena
Relaxation Processes
Transition Probability
Chapter 3: Hyperfine Structure
Nuclear Hyperfine Splitting
Radicals Containing One Proton
Spin Hamiltonian
Selection Rules
Radicals Containing a Set of Equivalent Protons
Radicals Containing Multiple Sets of Equivalent Protons
Radicals Containing Other Nuclei of Spin I = 1/2
Radicals Containing Nuclei with Spin I > 1/2
Aromatic Radicals
Origin of Hyperfine Interaction
(a) Dipolar Interaction
(b) Isotropic Hyperfine Interaction
(c) Spin Polarization
Sigma Radicals
Assignment of Spectra Using Huckel MOs
Alternant Hydrocarbons
Hyperfine Splitting Constants
Second Order Splitting
Applications
Identification and Structure Elucidation
Study of Transient Paramagnetic Species
Biochemical Applications
Analytical Applications
Chapter 4: Experimental Aspects: ESR
The ESR Spectrometer
Source
Sample cavity
Magnet
Sampling Procedure
Reference Spectra
Determination of g–Value
Chapter 5: Spectral Characteristics: Line Width and Anisotropy
Line Width
Introduction
Lifetime Broadening
Inhomogeneous Broadening
Homogeneous Broadening
Other Factors Affecting Line Width
Anisotropy
Anisotropy in g–Factor
Anisotropy in A-Values
Chapter 6: Dynamic Processes
Introduction
General Model for Interconversion
Electron Spin Exchange
Electron Transfer
Proton Exchange
Fluxional Molecules
Chapter 7: The Triplet State
General Remarks
Spin Transitions in Triplet State
Effect of Dipolar Field
Zero-Field Splitting
Spectra of Naphthalene Triplet
Hyperfine and Zero-Field Splitting in Triplet State Spectra
Chapter 8 : Transition Metal Complexes
Introduction
Features of the Spectra of Transition Metal Complexes
Energy Levels in a Metal Ion
Russell-Saunders Coupling
Hund’s Rules
Spin-Orbit Coupling
Effect of Crystal Field on d Orbitals
Effect of Crystal Field on g–Values
Jahn-Teller and Kramers Theorems
Spectra of First Transition Series : A Survey
(a) 3d 1 and 3d 9 Ions
(b) 3d 2 and 3d 8 Ions
(c) 3d 3 and 3d 7 Ions
(d) 3d 4 and 3d 6 Ions
(e) 3d 5 Ion
Chapter 9:Double Resonance Techniques
Introduction
Electron–Nuclear Double Resonance
Electron–Electron Double Resonance
General References
Exercises
Part Two: Nuclear Magnetic Resonance
Chapter 10: General Principles
Nuclear Spin and Magnetic Moment
Resonance Frequencies
Population of Energy Levels
Larmor Precession
The NMR Spectrum
Relaxation Processes
Chapter 11: Chemical Shift
Shielding Constant
Chemical Shift
Measurement of Peak Intensity
Measurement of Chemical Shifts
Reference Compounds
Simple Applications of Chemical Shift
Interpreting Chemical Shift
Origin of Shielding Constant
(a) Local Diamagnetic Shielding
(b) Neighbouring Group Anisotropy
(c) Ring Current
(d) Local Paramagnetic Shielding
(e) Contact Interaction
(f) Hydrogen Bonding
Chapter 12: Spin-Spin Coupling
Scalar Coupling
The Energy Levels of Coupled Systems
First Order Spectra
Nomenclature for Spin Systems
Patterns of Coupling
(i) AX System
(ii) AX2 System
(iii) AX3 System
(iv) AXn System
(v) AMX System
(vi) System with I ≥ 1
Observed Coupling Constants
Two-Bond Coupling
Three-Bond Coupling
Long-Range Coupling
Second Order Spectra
(i) AB System
(ii) AB2 System
(iii) ABX System
Origin of Spin–Spin Coupling
(i) Contact Interaction
(ii) Dipolar Interaction
Aids in the Analysis of Spectra
(i) Varying Magnetic Field
(ii) Isotopic Substitution
(iii) Computation of Spectra
Chapter 13: Experimental Aspects: NMR
FT NMR Spectrometer
(i) Magnet
(ii) Radiofrequency Transmitter
(iii) NMR Probe
(iv) Computer
Radiofrequency Pulses
Theory of NMR Experiment
Larmor Precession and Relaxation
The NMR Spectrum
Calibration
Advantages of FT NMR
Sampling Procedure
Variable Temperature NMR
Chapter 14: Dynamic NMR Spectroscopy
Introduction
Symmetrical Two–Site Exchange
Slow Exchange
Fast Exchange
Intermediate Exchange
Barrier to Internal Rotation
Unsymmetrical Two–Site Exchange
Ring Inversion
Fluxional Molecules
Intermolecular Exchange Processes
Proton Exchange
Intramolecular Exchange Processes
Keto-Enol Tautomerism
Fluorophosphoranes
Organometallic Compounds
Substituted Ethanes
Chapter 15: Spectra of Other Nuclei: 13C, 19F and 31P
General Remarks
Carbon-13 NMR
Peak Assignments
Off–Resonance Decoupling
Gated Decoupling
Other NMR Experiments
Polarization Transfer Experiment
Attached Proton Test (APT)
INEPT Spectra
DEPT Spectra
13C Chemical Shifts
13C—1H Coupling Constants
19F NMR
Chemical Shifts
Coupling Constants
Some Examples
31P NMR
Chemical Shifts
Coupling Constants
Some Examples
Geometrical Isomers
Two–Bond Coupling
Long Range Coupling
Chapter 16: Relaxation Processes
General Remarks
Spin–Lattice Relaxation
Spin–Spin Relaxation
Measurement of Relaxation Times
Measurement of T1 : Inversion Recovery Method
Measurement of T2: Spin Echoes Method
Quadrupolar Relaxation
Effect of Quadrupolar Relaxation on the Spectrum
Applications of Relaxation Times
Chapter 17: Multiple Resonance Techniques
Homonuclear Double Resonance
Heteronuclear Double Resonance
Broad Band Decoupling
Off–Resonance Decoupling
Gated Decoupling
Spin Tickling
Sign of the Coupling Constants
Coupling with Low–Abundant Nuclei
The Nuclear Overhauser Effect
Internuclear Double Resonance
Chapter 18: Selected Topics
Spectra of Paramagnetic Materials
Contact Shift
Origin of Contact Shift
Pseudo Contact Shift
Application of Contact Shifts
Diamagnetic Complexes
Spectra of Free Radicals
Lanthanide Shift Reagents
Magnetic Susceptibility Measurement
Solid State NMR
Wide Line NMR
Magic Angle Spinning
Applications
Magnetic Resonance Imaging
Chapter 19: Two-Dimensional NMR Spectroscopy
Introduction
Principles of 2D NMR
Preparation
Evolution
Mixing
Detection
2D NMR Experiment
Presentation of 2D NMR Spectra
1H–1H COSY
Modification of COSY
(a) COSY-DQF
(b) COSY 45
(c) COSY-LR (Long Range COSY)
HETCOR (1H – 13C COSY)
(a) Heteronuclear Multiple Quantum Coherence (HMQC)
(b) Heteronuclear Multiple Bond Connectivity (HMBC)
J–Resolved Spectra
2D Nuclear Overhauser Spectroscopy (NOESY)
2D INADEQUATE Spectroscopy
Applications of 2D NMR
General References
Exercises
Part Three: Nuclear Quadrupole Resonance
Chapter 20: Nuclear Quadrupole Resonance Spectroscopy
Introduction
Nuclear Quadrupole Moment
Electric Field Gradient
The Asymmetry Parameter
Nuclear Quadrupole Transitions
(a) Axially Symmetric Molecules
(b) Axially Non–Symmetric Molecules
Effect of an External Magnetic Field
Applications
(i) Chemical Bonding and Structure
(ii) Solid State Effects
(iii) Hydrogen Bonding
Experimental Aspects
General References
Exercises
Appendices
Appendix I: General Data and Fundamental Constants
Appendix II: Hückel Molecular Orbitals
Appendix III: Solutions to Exercises
Index
Backcover
Citation preview
TM
Third Edition
Introduction to
ESR, NMR, NQR Third Edition
2D NMR spectroscopy C , 19F and 31P
Introduction to
MAGNETIC RESONANCE SPECTROSCOPY v5 v6 v4
D.N. Sathyanarayana
978-81-94778-76-9
ESR, NMR, NQR
Introduction to
ESR, NMR, NQR
MAGNETIC RESONANCE SPECTROSCOPY
MAGNETIC RESONANCE SPECTROSCOPY
v3
v7 v8
v1
Third Edition
` 995/-
v2
v9
D.N. Sathyanarayana Distributed by:
9 788194 778769
TM
INTRODUCTION TO
Magnetic Resonance Spectroscopy ESR, NMR, NQR
INTRODUCTION TO
Magnetic Resonance Spectroscopy ESR, NMR, NQR Third Edition
D.N. SATHYANARAYANA Formerly, Chairman, Department of Inorganic and Physical Chemistry Indian Institute of Science, Bangalore
Introduction to Magnetic Resonance Spectroscopy Esr, Nmr, Nqr, 2/E Authors: D.N. Sathyanarayana Published by I.K. International Pvt. Ltd. 4435, 36/7, Ansari Rd, Daryaganj, New Delhi, Delhi 110002 ISBN: 978-81-947787-6-9 EISBN: 978-81-947787-7-6 ©Copyright 2020 I.K. International Pvt. Ltd., New Delhi-110002. This book may not be duplicated in any way without the express written consent of the publisher, except in the form of brief excerpts or quotations for the purposes of review. The information contained herein is for the personal use of the reader and may not be incorporated in any commercial programs, other books, databases, or any kind of software without written consent of the publisher. Making copies of this book or any portion for any purpose other than your own is a violation of copyright laws. Limits of Liability/disclaimer of Warranty: The author and publisher have used their best efforts in preparing this book. The author make no representation or warranties with respect to the accuracy or completeness of the contents of this book, and specifically disclaim any implied warranties of merchantability or fitness of any particular purpose. There are no warranties which extend beyond the descriptions contained in this paragraph. No warranty may be created or extended by sales representatives or written sales materials. The accuracy and completeness of the information provided herein and the opinions stated herein are not guaranteed or warranted to produce any particulars results, and the advice and strategies contained herein may not be suitable for every individual. Neither Dreamtech Press nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. Trademarks: All brand names and product names used in this book are trademarks, registered trademarks, or trade names of their respective holders. Dreamtech Press is not associated with any product or vendor mentioned in this book. Edition: 2020 Printed at: Rekha Printers
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Preface to the Third Edition The main objective of 'Introduction to Magnetic Resonance Spectroscopy' is to acquaint readers with more details than that found in basic spectroscopy books. What has not changed in this edition is the breadth of coverage, one of the features that has led to its wide use as a graduate level text and reference material. In Magnetic Resonance Spectroscopy wide range of structural techniques are discussed in depth. These techniques are used in organic chemistry as much as in inorganic chemistry. Several new problems have been added and detailed solutions are provided for all the end-of-chapter problems. This is deliberate to make the students aware of the problem solving strategies. Solving problems is a very real part of the curriculum. I have attempted to correct as many as possible of the errors that appeared in the earlier edition. It is a pleasure to thank Professor E. Arunan, the chairman of the Department for extending all the facilities. I thank my wife Vijayalakshmi and our sons Supradeep and Sushirdeep for their cooperation and support. D.N. SATHYANARAYANA
Preface to the Second Edition
I am happy to note that my book has been quite favourably accepted by students and teachers of various universities and for this I am grateful. Readers of this book will, if they are familiar with the first edition, immediately recognize that there are no major changes. I have continued to handle other aspects of the book in the same way as in the earlier edition. It has always been my desire to keep the physical size of the book to about that of the first edition. This book is intended for graduate students and research workers of chemistry, physics and biological sciences who need a text that is pitched at a modest relatively non-mathematical level and that can be applied in solving problems related to structure and behaviour of organic and inorganic molecules. The theoretical basis of the more important effects are given where it seemed appropriate. I wish to record my sincere thanks to Professor A.G. Samuelson, the Chairman of the Department for providing the facilities. My thanks are due to my wife, Vijayalakshmi and sons, Supradeep and Sushirdeep for their forbearance and encouragement. Care has been taken to make the book error and obscurities free. Feedback from teachers and students especially concerning errors and deficiencies in this edition are welcome. Suggestions for further improvement of the text will be greatly appreciated. Finally I am deeply grateful to I.K. Publishers at New Delhi and Bangalore for believing in this project from its onset and overseeing various aspects of its production. Bangalore July 18, 2013
D.N. SATHYANARAYANA SATHYANARAYANA
Preface to the First Edition The contents of this book are concerned solely with spectra arising from the interaction of magnetic field component of the electromagnetic radiation with nuclear and electron spins. The chapters deal successively with the fundamentals of electron spin resonance, nuclear magnetic resonance and nuclear quadrupole resonance spectroscopy. This book has the aim of providing an introduction to magnetic resonance spectroscopy while making use of illustrations. The book is primarily aimed at students taking an introductory course in magnetic resonance spectroscopy at the Masters Degree level and those entering research in chemistry, biochemistry, pharmacy and physics. It should also serve as a source book for self study. They hopefully will find the book easy to read and understand. The past three decades have witnessed the development of nuclear magnetic resonance spectroscopy into one of the most powerful analytical tools. An indepth understanding of this advanced technology is necessary for fruitful applications of magnetic resonance spectroscopy. In a subject as large as magnetic resonance spectroscopy, a book of this length presents the author with a difficult dilemma; one can either attempt to treat all areas equally, albeit at a superficial level, or one is forced to restrict the scope so as to achieve a reasonable coverage of selected topics. The second approach has been adopted here for two reasons. First, it provides for greater coherence and a more satisfying level of exposition. Secondly, with the tremendous strides, magnetic resonance spectroscopy is now the norm rather than the exception. The first part covers the basic material necessary for understanding the topic of ESR spectroscopy. The subsequent parts, part II and part III, have dealt with NMR and NQR spectroscopies. Many of my students have contributed to the development of the book – in particular I wish to thank Dr. Priyadarsi De, Dr. S. Subrahmanya and Dr. B. Veerendra. I am profoundly grateful to Professor S.N Bhat, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, Professor Arabinda Ray, Sardar Patel University, V. V. Nagar, Gujarat and Professor S. Manogaran, Indian Institute of Technology, Kanpur, who have carefully and perceptively read the whole manuscript and have made constructive criticisms. I am most thankful to the various authors and publishers who have given their permission to reproduce the respective copyrighted material. I would like to thank Professor P. Balaram, the Director, Indian Institute of Science, Bangalore for general help. My special thanks are due to Professor A.R Chakravarty, the former Chairman, Professor K.L. Sebastian, the former
Zxii
Preface to Preface the First Edition
Chairman, and Professor A.G. Samuelson, the Chairman, Department of Inorganic and Physical Chemistry of the Indian Institute of Science, for their full support by extending all the facilities to me. I am greatly thankful to my esteemed colleague Professor V. Krishnan for his help which has enabled me to complete this work. The Financial assistance received from the Department of Science and Technology, New Delhi, towards the writing of the book under the scheme “USERS” is gratefully acknowledged. I gratefully acknowledge the financial assistance received towards the preparation of the manuscript by the Curriculum Development Cell of the Centre for Continuing Education of the Indian Institute of Science. I would like to record my appreciation of the assistance of Mr. C.Sridhar for his expert typing of the manuscript, Mr. M.B. Madhusudhana Reddy, Chemistry Department, Bangalore University and Mr. M. Srinivasa Murthy for the preparation of some of the drawings. I would like to thank my publishers for their full support throughout the production process. It is inevitable that in a book of this size and complexity that there will be occassional errors. I shall be grateful to the readers who point out any errors and/or make other constructive suggestions. It is always a joy and a privilege to express my gratitude to my wife, Vijayalakshmi and our children, Supradeep and Sushirdeep for their love, support and emotional sustenance during the writing of this book.
D.N. SATHYANARAYANA
Acknowledgements It is not feasible to list all the sources which have helped me in writing this text. However, I would like to specially acknowledge the following works from which some of the illustrations have been adopted, I am most thankful to these authors and publishers for the permission to reproduce the copyright material. The permission of the following individuals, institutions, and journals for reproduction of illustrations is gratefully acknowledged. Fig. 3.28
A. Carrington and J.dos Santos–Veiga, Mol. Phys. 5, 21 (1962).
Figs. 3.30 and 6.1
J.A. Weil, J.R. Bolton and J.E. Wertz, Electron Paramagnetic Resonance, Wiley–Interscience, New York (1994).
Fig. 3.34
D.H. Levy and R.J. Meyer, J. Chem. Phys. 41, 1062 (1964).
Fig. 4.3
Professor K.R. Nagasundara and Dr. S. Rekha, Department of Chemistry, Bangalore University, Bangalore.
Fig. 6.2
R.S. Drago, Physical Methods in Chemistry, W.B. Saunders & Co., Philadelphia (1977).
Fig. 7.6
C.A. Hutchison, Jr. and B.W. Mangum, J. Chem. Phys. 34, 908 (1961).
Fig. 7.8
R.E. Jesse, P. Biloen, R. Prins, J.D.W. van Voorst and G.J. Hoijtink, Mol. Phys. 6, 633 (1963).
Fig. 8.12
A.H. Maki and B.R. McGarvey, J. Chem. Phys. 29, 35 (1958).
Fig. 8.14
B.J. Hathaway and D.E. Billing, Coord. Chem. Revs. 5, 143 (1970).
Fig. 9.3
G. Labrauze, J.B. Raynoor and E. Samuel, J. Chem. Soc. Dalton Trans. 2425 (1980).
Figs. 12.7 and 19.17
P.J. Hore, Nuclear Magnetic Resonance, Oxford University Press, Oxford (1995).
Fig. 14.20
Ramey, O’Brien, Hasegawa and Borchert, J.Chem. Phys. 69, 3418 (1965).
Fig. 14.22
F.A. Cotton and D.L. Hunter, J. Amer. Chem. Soc. 98, 1413 (1976).
Fig. 15.7
K.G.R. Pachler and P.L. Wessels, J. Magn. Reson. 12, 337 (1973).
Figs. 15.9, A–U Rahman and M.I. Choudhary, Solving Problems with NMR 15.15 and 19.22 Spectroscopy, Academic Press, San Diego, California (1996).
xiv xii
Acknowledgements
Fig. 15.12
H. Gunther, NMR Spectroscopy, Basic Principles, Concepts and Applications in Chemistry, 2nd edition, John Wiley, New York (1995).
Fig. 16.6
M.L. Martin, J.J. Delpuech and G.J. Martin, Practical NMR Spectroscopy, Wiley, New York (1986).
Fig. 16.10
J.W. Akitt, NMR and Chemistry, An Introduction to the Fourier Transform Multinuclear Era, 2nd edition, Chapman and Hall, London (1983).
Fig. 17.2
Farrar, Johannensen and Coyle, J. Chem. Phys. 49, 281 (1968).
Fig. 18.4
E. de Boer and C. McLean, Mol. Phys. 9, 191 (1965).
Fig. 18.6
S.A. Richards, Laboratory Guide to Proton NMR Spectroscopy, Blackwell Scientific Publications, Oxford (1988).
Fig. 18.8
From Bruker CXP Application Notes.
Fig. 18.9
R.K. Harris, Nuclear Magnetic Resonance Spectroscopy, Pitman, London (1983).
Figs. 19.7 and 19.21
J.K.M. Sanders and B.K. Hunter, Modern NMR Spectroscopy, Oxford University Press, Oxford (1987).
Fig. 19.12
G. Solomons and C. Fryhle, Organic Chemistry, John Wiley and Sons Inc., New York (2000).
Fig. 20.4
E.A. Kravchenko, N.V. Timofeeva J. Mol. Struct. 58, 253 (1980).
and
G.Z. Vinogradova,
Contents Preface to the Third Edition Preface to the Second Edition Preface to the First Edition Acknowledgements 1
General Introduction Introduction Electromagnetic Radiation Number of Spectral Lines Spectral Line Width Band Intensities Spin Transitions Exercises
vii ix xi xiii 1 1 2 4 4 6 7 8
PART ONE: ELECTRON SPIN RESONANCE 2
Basic Theory General Remarks Electron Spin and Magnetic Moment ESR Transitions Selection Rules g–Factor Presentation of Spectra Interaction of Magnetic Dipoles with Microwave Radiation Larmor Precession Resonance Phenomena Relaxation Processes Transition Probability
13 13 14 16 18 18 19 20 21 22 24 26
3
Hyperf ine Structure Nuclear Hyperf ine Splitting Radicals Containing One Proton Spin Hamiltonian Selection Rules Radicals Containing a Set of Equivalent Protons Radicals Containing Multiple Sets of Equivalent Protons Radicals Containing Other Nuclei of Spin I = 1/2 Radicals Containing Nuclei with Spin I > 1/2 Aromatic Radicals Origin of Hyperfine Interaction (a) Dipolar Interaction (b) Isotropic Hyperfine Interaction (c) Spin Polarization
29 29 29 31 34 35 40 45 46 50 51 51 53 55
xvi
Contents
Sigma Radicals Assignment of Spectra Using Huckel MOs Alternant Hydrocarbons Hyperfine Splitting Constants Second Order Splitting Applications Identification and Structure Elucidation Study of Transient Paramagnetic Species Biochemical Applications Analytical Applications
59 61 63 67 69 69 69 70 71 71
4
Experimental Aspects: ESR The ESR Spectrometer Source Sample cavity Magnet Sampling Procedure Reference Spectra Determination of g–Value
73 73 73 73 74 75 76 77
5
Spectral Characteristics: Line Width and Anisotropy Line Width Introduction Lifetime Broadening Inhomogeneous Broadening Homogeneous Broadening Other Factors Affecting Line Width Anisotropy Anisotropy in g–Factor Anisotropy in A-Values
81 81 81 82 84 85 85 85 85 91
6
Dynamic Processes Introduction General Model for Interconversion Electron Spin Exchange Electron Transfer Proton Exchange Fluxional Molecules
93 93 93 95 96 97 97
7
The Triplet State General Remarks Spin Transitions in Triplet State Effect of Dipolar Field Zero-Field Splitting Spectra of Naphthalene Triplet Hyperfine and Zero-Field Splitting in Triplet State Spectra
99 99 100 101 102 104 107
Contents
8
9
xvii
Transition Metal Complexes Introduction Features of the Spectra of Transition Metal Complexes Energy Levels in a Metal Ion Russell-Saunders Coupling Hund’s Rules Spin-Orbit Coupling Effect of Crystal Field on d Orbitals Effect of Crystal Field on g–Values Jahn-Teller and Kramers Theorems Spectra of First Transition Series : A Survey (a) 3d 1 and 3d 9 Ions (b) 3d 2 and 3d 8 Ions (c) 3d 3 and 3d 7 Ions (d) 3d 4 and 3d 6 Ions (e) 3d 5 Ion
109 109 110 113 113 115 117 118 122 123 124 124 133 134 137 138
Double Resonance Techniques Introduction Electron–Nuclear Double Resonance Electron–Electron Double Resonance
142 142 142 146
General References Exercises
148 148
PART TWO: NUCLEAR MAGNETIC RESONANCE 10
General Principles Nuclear Spin and Magnetic Moment Resonance Frequencies Population of Energy Levels Larmor Precession The NMR Spectrum Relaxation Processes
159 159 162 164 165 167 168
11
Chemical Shift Shielding Constant Chemical Shift Measurement of Peak Intensity Measurement of Chemical Shifts Reference Compounds Simple Applications of Chemical Shift Interpreting Chemical Shift Origin of Shielding Constant (a) Local Diamagnetic Shielding (b) Neighbouring Group Anisotropy
171 171 172 173 174 177 179 180 182 183 185
xviii
Contents
(c) Ring Current (d) Local Paramagnetic Shielding (e) Contact Interaction (f) Hydrogen Bonding
189 192 192 193
12
Spin-Spin Coupling Scalar Coupling The Energy Levels of Coupled Systems First Order Spectra Nomenclature for Spin Systems Patterns of Coupling (i) AX System (ii) AX2 System (iii) AX3 System (iv) AXn System (v) AMX System (vi) System with I ≥ 1 Observed Coupling Constants Two-Bond Coupling Three-Bond Coupling Long-Range Coupling Second Order Spectra (i) AB System (ii) AB2 System (iii) ABX System Origin of Spin–Spin Coupling (i) Contact Interaction (ii) Dipolar Interaction Aids in the Analysis of Spectra (i) Varying Magnetic Field (ii) Isotopic Substitution (iii) Computation of Spectra
196 196 198 200 201 202 203 204 204 205 207 208 210 213 214 215 216 216 220 222 225 225 227 227 227 228 228
13
Experimental Aspects: NMR FT NMR Spectrometer (i) Magnet (ii) Radiofrequency Transmitter (iii) NMR Probe (iv) Computer Radiofrequency Pulses Theory of NMR Experiment Larmor Precession and Relaxation The NMR Spectrum Calibration Advantages of FT NMR
229 229 230 233 233 233 234 236 236 241 242 243
Contents
xix
Sampling Procedure Variable Temperature NMR
244 245
14
Dynamic NMR Spectroscopy Introduction Symmetrical Two–Site Exchange Slow Exchange Fast Exchange Intermediate Exchange Barrier to Internal Rotation Unsymmetrical Two–Site Exchange Ring Inversion Fluxional Molecules Intermolecular Exchange Processes Proton Exchange Intramolecular Exchange Processes Keto-Enol Tautomerism Fluorophosphoranes Organometallic Compounds Substituted Ethanes
246 246 247 248 249 249 251 253 254 256 258 258 260 260 262 262 266
15
Spectra of Other Nuclei: 13C, 19F and 31P General Remarks Carbon-13 NMR Peak Assignments Off–Resonance Decoupling Gated Decoupling Other NMR Experiments Polarization Transfer Experiment Attached Proton Test (APT) INEPT Spectra DEPT Spectra 13 C Chemical Shifts 13 C—1H Coupling Constants 19 F NMR Chemical Shifts Coupling Constants Some Examples 31 P NMR Chemical Shifts Coupling Constants Some Examples Geometrical Isomers Two–Bond Coupling Long Range Coupling
269 269 269 271 272 275 275 275 279 282 286 289 293 296 296 297 298 300 300 301 302 304 305 306
xx
16
Contents
Relaxation Processes General Remarks Spin–Lattice Relaxation Spin–Spin Relaxation Measurement of Relaxation Times Measurement of T1 : Inversion Recovery Method Measurement of T2: Spin Echoes Method Quadrupolar Relaxation Effect of Quadrupolar Relaxation on the Spectrum Applications of Relaxation Times
307 307 307 310 313 313 317 321 322 323
Multiple Resonance Techniques Homonuclear Double Resonance Heteronuclear Double Resonance Broad Band Decoupling Off–Resonance Decoupling Gated Decoupling Spin Tickling Sign of the Coupling Constants Coupling with Low–Abundant Nuclei The Nuclear Overhauser Effect Internuclear Double Resonance
325 325 327 329 330 331 332 334 336 337 342
18
Selected Topics Spectra of Paramagnetic Materials Contact Shift Origin of Contact Shift Pseudo Contact Shift Application of Contact Shifts Diamagnetic Complexes Spectra of Free Radicals Lanthanide Shift Reagents Magnetic Susceptibility Measurement Solid State NMR Wide Line NMR Magic Angle Spinning Applications Magnetic Resonance Imaging
345 345 345 348 351 351 353 353 355 358 359 359 360 364 365
19
Two-Dimensional NMR Spectroscopy Introduction Principles of 2D NMR Preparation Evolution Mixing Detection
368 368 368 370 370 370 370
17
Contents
xxi
2D NMR Experiment Presentation of 2D NMR Spectra 1 H–1H COSY Modification of COSY (a) COSY-DQF (b) COSY 45 (c) COSY-LR (Long Range COSY) HETCOR (1H – 13C COSY) (a) Heteronuclear Multiple Quantum Coherence (HMQC) (b) Heteronuclear Multiple Bond Connectivity (HMBC) J–Resolved Spectra 2D Nuclear Overhauser Spectroscopy (NOESY) 2D INADEQUATE Spectroscopy Applications of 2D NMR
371 373 374 378 378 380 380 381 385 386 388 389 393 398
General References Exercises
400 401
PART THREE: NUCLEAR QUADRUPOLE RESONANCE 20
Nuclear Quadrupole Resonance Spectroscopy Introduction Nuclear Quadrupole Moment Electric Field Gradient The Asymmetry Parameter Nuclear Quadrupole Transitions (a) Axially Symmetric Molecules (b) Axially Non–Symmetric Molecules Effect of an External Magnetic Field Applications (i) Chemical Bonding and Structure (ii) Solid State Effects (iii) Hydrogen Bonding Experimental Aspects
419 419 420 422 424 427 427 430 433 435 435 438 441 441
General References Exercises
443 443
Appendices Appendix I: General Data and Fundamental Constants Appendix II: Hückel Molecular Orbitals Appendix III: Solutions to Exercises
447 448 456
Index
487
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