High Resolution NMR (eBook)

Front Cover 1
High Resolution NMR: Theory and Chemical Applications 4
Copyright Page 5
Preface 6
Acknowledgments 8
Table of Contents 10
High Resolution NMR 14
Chapter 1. Introduction 16
1.1 Historical 16
1.2 High Resolution NMR 17
References 25
Chapter 2. The Theory of NMR 27
2.1 Nuclear Spin and Magnetic Moment 27
2.2 Classical Mechanical Description of NMR 28
2.3 Quantum Mechanical Description of NMR 32
2.4 Effect of the Boltzmann Distribution 34
2.5 Spin-Lattice Relaxation 36
2.6 Line Widths 38
2.7 Saturation 40
2.8 The Bloch Equations Nuclear Induction
2.9 Ringing 43
References 45
Problems 45
Chapter 3. Instrumentation and Techniques 47
3.1 Basic NMR Apparatus 47
3.2 Requirements for High Resolution NMR 48
3.3 Modulation and Phase Detection 52
3.4 Field/Frequency Control 52
3.5 Signal/Noise and Size of Sample 56
3.6 Superconducting Magnets 59
3.7 Intensity Measurements 60
3.8 References 61
3.9 Magnetic Susceptibility Measurements 63
3.10 Frequency Calibration 64
3.11 Control of Sample Temperature 65
3.12 Useful Solvents 65
3.13 Sampling Techniques 66
3.14 Micro Techniques 69
3.15. Adiabatic Rapid Passage 71
3.17 Double Resonance Techniques 71
References 71
Problems 72
Chapter 4. Chemical Shifts 74
4.1 The Origin of Chemical Shifts 74
4.2 Reference Compounds 75
4.3 Chemical Shift Scales 75
4.4 Magnetic Susceptibility Correction 78
4.5 Empirical Correlations of Chemical Shifts 79
4.6 Theory of Chemical Shifts 83
4.7 Effect of Electron Density 85
4.8 Magnetic Anisotropy and Chemical Shifts 88
4.9 Ring Currents 92
4.10 Paramagnetic Species 95
4.11 Nuclei Other Than Hydrogen 95
4.12 Tabulations of Chemical Shifts and Spectra 95
4.13 Empirical Estimation of Chemical Shifts 97
References 97
Problems 99
Chapter 5. Electron-Coupled Spin-Spin Interactions 101
5.1 Origin of Spin-Spin Coupling 101
5.2 Coupling between Groups of Equivalent Nuclei 103
5.3 First-Order Analysis 104
5.4 Signs of Coupling Constants 108
5.5 Theory of Spin-Spin Coupling 109
5.6 Some Observed Coupling Constants 110
5.7 Correlation of Coupling Constants with Other Physical Properties 118
References 120
Problems 121
Chapter 6. The Use of NMR in Structure Elucidation 123
6.1 A Systematic Approach to the Interpretation of NMR Spectra 123
6.2 Spectra of Polymers in Solution 130
References 132
Problems 132
Chapter 7. Analysis of Complex Spectra 134
7.1 Notation 134
7.2 Energy Levels and Transitions in an AX System 136
7.3 Quantum Mechanical Formalism 138
7.4 Nuclear Spin Basis Functions 140
7.5 The Spin Hamiltonian 140
7.6 The Two-Spin System without Coupling 142
7.7 Factoring the Secular Equation 145
7.8 Two Coupled Spins 146
7.9 Selection Rules and Intensities 149
7.10 The AB Spectrum 150
7.11 Spectral Contributions from Equivalent Nuclei 153
7.12 Symmetry of Wave Functions 154
7.13 Summary of Rules for Calculating Spectra 156
7.14 The Three-Spin System: ABC 158
7.15 The A2B System 159
7.16 The A3B System Subspectral Analysis
7.17 The ABX System 164
7.18 Analysis of an ABX Spectrum 167
7.19 Relative Signs o f JAX and JBX in an ABX Spectrum 173
7.20 ABX Patterns Deceptively Simple Spectra
7.21 "Virtual Coupling" 178
7.22 The AA' BB' and AA'XX' Systems 181
7.23 Other Complex Spectra 185
7.24 Aids in the Analysis of Complex Spectra 185
7.25 Use of Liquid Crystals as Solvents 188
References 189
Problems 190
Chapter 8. Theory and Application of Double Resonance 193
8.1 Notation and Terminology 193
8.2 Experimental Techniques 194
8.3 Theory of Double Resonance 196
8.4 Structure Elucidation 201
8.5 Location of " Hidden " Lines 203
8.6 Determination of Chemical Shifts 204
8.7 Relative Signs of Coupling Constants 207
8.8 Determination of Energy Level Arrangements 211
8.9 Other Applications 214
References 215
Problems 215
Chapter 9. Relaxation 217
9.1 Processes for Spin-Lattice Relaxation 217
9.2 Nuclear Magnetic Dipole Interactions 218
9.3 The Effect of Anisotropic Shielding 220
9.4 Electric Quadrupole Relaxation 221
9.5 Relaxation by Paramagnetic Substances 222
9.6 Chemical Applications 223
9.7 Measurement of Relaxation Times 224
References 228
Problems 228
Chapter 10.Effects of Exchange Processes 229
10.1 Spectra of Exchanging Systems 229
10.2 Theory of Chemical Exchange 233
10.3 Collapse of Spin Multiplets 234
10.4 More Complete Theories of Exchange 237
10.5 Double Resonance and Pulse Techniques 237
10.6 Asymmetry and Internal Rotation 239
References 242
Problems 243
Chapter 11. Solvent Effects and Hydrogen Bonding 244
11.1 Medium Effects on Chemical Shifts 244
11.2 Solvent Effects on Coupling Constants 246
11.3 Solvent Effects on Relaxation and Exchange Rates 247
11.4 Hydrogen Bonding 247
References 249
Problem 250
Chapter 12. Use of NMR in Quantitative Analysis 251
12.1 Advantages of NMR in Quantitative Analysis 251
12.2 Drawbacks and Problems in the Use of NMR in Quantiative Analysis 252
12.3 Some Analytical Uses of NMR 253
References 255
Appendix A: Nuclear Spins, Magnetic Moments, and Resonance Frequencies0 256
Appendix B: Proton NMR Spectra of "Unknowns" 268
Appendix C: General NMR References 308
Appendix D: Answers to Selected Problems 310
Subject Index 319