High-Resolutio n NMR Techniques i n Organic Chemistry TIMOTHY D W CLARIDGE

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1 High-Resolutio n NMR Techniques i n Organic Chemistry TIMOTHY D W CLARIDGE

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3 Foreword Preface Acknowledgements V VI I X Chapter 1. Introduction 1.1. The development of high-resolution NMR Modern high-resolution NMR and this book What this book contains Pulse sequence nomenclature Applying modern NMR techniques 8 References 1 2 Chapter 2. Introducing high-resolution NM R 2.1. Nuclear spin and resonance The vector model of NMR The rotating frame of reference Pulses Chemical shifts and couplings Spin-echoes Time and frequency domains Spin relaxation Longitudinal relaxation : establishing equilibrium Measuring T l with the inversion-recovery sequence Transverse relaxation : loss of magnetisation in the x-y plane Measuring T 2 with a spin-echo sequence Mechanisms for relaxation The path to relaxation Dipole-dipole relaxation Chemical shift anisotropy relaxation Spin-rotation relaxation Quadrupolar relaxation 4 0 References 4 3 Chapter 3. Practical aspects of high-resolution NM R 3.1. An overview of the NMR spectrometer Data acquisition and processing Pulse excitation Signal detection Sampling the FID Quadrature detection Phase cycling Dynamic range and signal averaging Window functions Phase correction Preparing the sample Selecting the solvent Reference compounds 77

4 Tubes and sample volumes Filtering and degassing Preparing the spectrometer The probe Tuning the probe The field-frequency lock Optimising the field homogeneity : shimming Spectrometer calibrations Radiofrequency pulses Pulsed field gradients Sample temperature Spectrometer performance tests Lineshape and resolution Sensitivity Solvent presaturation 109 References 11 0 Chapter 4. One-dimensional technique s 4.1. The single-pulse experiment Optimising sensitivity Quantitative measurements and integration Spin decoupling methods The basis of spin decoupling Homonuclear decoupling Heteronuclear decoupling Spectrum editing with spin-echoes The J-modulated spin-echo APT Sensitivity enhancement and spectrum editing Polarisation transfer INEPT DEPT PENDANT Observing quadrupolar nuclei 143 References 145 Chapter 5. Correlations through the chemical bond I : Homonuclear shift correlation 5.1. Introducing two-dimensional methods Generating a second dimension Correlation spectroscopy (COSY) Correlating coupled spins Interpreting COSY Peak fine structure Practical aspects of 2D NMR D lineshapes and quadrature detection Axial peaks Instrumental artefacts D data acquisition D data processing Coherence and coherence transfer Coherence-transfer pathways Gradient-selected spectroscopy Signal selection with pulsed field gradients Phase-sensitive experiments PFGs in high-resolution NMR Practical implementation of PFGs Alternative COSY sequences Which COSY approach? Double-quantum filtered COSY (DQF-COSY) COSY-ß 197

5 Delayed-COSY: detecting small couplings Relayed-COSY Total correlation spectroscopy (TOCSY) The TOCSY sequence Using TOCSY Implementing TOCSY Correlating dilute spins : INADEQUATE D INADEQUATE D INADEQUATE Implementing INADEQUATE Variations on INADEQUATE 21 6 References 21 8 Chapter 6. Correlations through the chemical bond II : Heteronuclear shift correlatio n 6.1. Introduction Sensitivity Heteronuclear single-bond correlation spectroscopy Heteronuclear multiple-quantum correlation (HMQC) Heteronuclear single-quantum correlation (HSQC) Practical implementations Hybrid experiments Heteronuclear multiple-bond correlation spectroscopy The HMBC sequence Applying HMBC Traditional X-detected correlation spectroscopy Single-bond correlations Multiple-bond correlations and small couplings 25 4 References 25 6 Chapter 7. Separating shifts and couplings : J-resolved spectroscopy 7.1. Introduction Heteronuclear J-resolved spectroscopy Measuring long-range proton-carbon coupling constants Practical considerations Homonuclear J-resolved spectroscopy Tilting, projections and symmetrisation Applications Practical considerations `Indirect' homonuclear J-resolved spectroscopy 27 3 References 27 4 Chapter 8. Correlations through space : The nuclear Overhauser effect 8.1. Introduction Definition of the NOE Steady-state NOEs NOEs in a two-spin system NOEs in a multispin system Summary Applications Transient NOEs NOE kinetics Measuring internuclear separations Rotating-frame NOEs Measuring steady-state NOEs : NOE difference Optimising difference experiments Measuring transient NOEs : NOESY The 2D NOESY sequence D NOESY sequences Applications 323

6 Measuring chemical exchange: EXSY Measuring rotating-frame NOEs : ROESY The 2D ROESY sequence D ROESY sequences Applications Measuring heteronuclear NOEs Experimental considerations 33 6 References 33 7 Chapter 9. Experimental method s 9.1. Composite pulses A myriad of pulses Inversion vs. refocusing Broadband decoupling and spin-locks Spin-locks Adiabatic pulses Selective excitation and shaped pulses Shaped soft pulses DANTE sequences Excitation sculpting Practical considerations Solvent suppression Presaturation Zero excitation Pulsed field gradients Recent methods Heterogeneous samples and MAS Diffusion-ordered spectroscopy 368 References 37 1 Appendix. Glossary of acronyms 373 Index 375