Nuclear Magnetic Resonance Spectroscopy An Introduction to Principles, Applications, and Experimental Methods

by Lambert, Joseph B.; Mazzola, Eugene P.

• ISBN13: 9780130890665
• ISBN10: 0130890669
• Edition: 1st
• Format: Paperback
• Copyright: 2003-03-13
• Publisher: Prentice Hall

Summary

This book offers complete coverage of classic (one-dimensional) NMR as well as up-to-date coverage of two-dimensional NMR and other modern methods.This book focuses on all aspects of NMR including classic methods, modern techniques, practical advice for execution of the NMR experiment, theory, and more.For practicing NMR spectroscopists who want a better understanding of their subject, professors who want a wider knowledge of NMR, preparative (synthetic) organic chemists in industry who want to have more information about how to prove the structures of the compounds they make, and analytical chemists in industry who actually carry out the experiments and want a better understanding of what they are doing.

Table of Contents

Preface	xi
Introduction	1	(30)
Magnetic Properties of Nuclei	1	(4)
The Chemical Shift	5	(3)
Excitation and Relaxation	8	(3)
Pulsed Experiments	11	(2)
The Coupling Constant	13	(6)
Quantitation and Complex Splitting	19	(2)
Commonly Studied Nuclides	21	(2)
Dynamic Effects	23	(2)
Spectra of Solids	25	(6)
Problems	27	(3)
Bibliography	30	(1)
Introductory Experimental Methods	31	(31)
The Spectrometer	31	(2)
Sample Preparation	33	(1)
Optimizing the Signal	34	(5)
Sample Tube Placement	34	(1)
Probe Adjustment	34	(1)
Field/Frequency Locking	35	(1)
Spectrometer Shimming	36	(3)
Determination of NMR Spectra: Acquisition Parameters	39	(9)
Number of Data Points	41	(1)
Spectral Width	41	(1)
Filter Bandwidth	42	(1)
Acquisition Time	42	(1)
Transmitter Offset	43	(1)
Flip Angle	43	(2)
Receiver Gain	45	(1)
Number of Scans	45	(1)
Steady-State Scans	46	(1)
Oversampling and Digital Filtration	46	(1)
Decoupling for X Nuclei	46	(1)
Typical NMR Experiments	47	(1)
Determination of NMR Spectra: Processing Parameters	48	(4)
Exponential Weighting	48	(1)
Zero Filling	49	(1)
FID Truncation and Spectral Artifacts	50	(1)
Resolution	51	(1)
Determination of NMR Spectra: Spectral Presentation	52	(6)
Signal Phasing and Baseline Correction	52	(3)
Zero Referencing	55	(1)
Determination of Certain NMR Parameters	56	(2)
Calibrations	58	(4)
Pulse Width (Flip Angle)	58	(2)
Decoupler Field Strength	60	(1)
Problems	61	(1)
Bibliography	61	(1)
The Chemical Shift	62	(36)
Factors that Influence Proton Shifts	62	(7)
Proton Chemical Shifts and Structure	69	(7)
Saturated Aliphatics	69	(2)
Unsaturated Aliphatics	71	(2)
Aromatics	73	(2)
Protons on Oxygen and Nitrogen	75	(1)
Programs for Empirical Calculations	76	(1)
Medium and Isotope Effects	76	(3)
Factors that Influence Carbon Shifts	79	(2)
Carbon Chemical Shifts and Structure	81	(7)
Saturated Aliphatics	82	(4)
Unsaturated Compounds	86	(2)
Carbonyl Groups	88	(1)
Programs for Empirical Calculation	88	(1)
Tables of Chemical Shifts	88	(10)
Problems	91	(6)
Bibliography	97	(1)
The Coupling Constant	98	(33)
First- and Second-Order Spectra	98	(1)
Chemical and Magnetic Equivalence	99	(5)
Signs and Mechanisms: One-Bond Couplings	104	(2)
Geminal Couplings	106	(3)
Vicinal Couplings	109	(3)
Long-Range Couplings	112	(3)
Spectral Analysis	115	(4)
Tables of Coupling Constants	119	(12)
Problems	122	(7)
Bibliography	129	(2)
Further Topics in One-Dimensional NMR	131	(41)
Spin--Lattice and Spin--Spin Relaxation	131	(5)
Reactions on the NMR Time Scale	136	(7)
Multiple Resonance	143	(5)
The Nuclear Overhauser Effect	148	(5)
Spectral Editing	153	(3)
Sensitivity Enhancement	156	(6)
Carbon Connectivity	162	(1)
Phase Cycling, Composite Pulses, and Shaped Pulses	163	(9)
Problems	166	(4)
Bibliography	170	(2)
Two-Dimensional NMR	172	(61)
Proton--Proton Correlation Through Coupling	172	(15)
Proton--Heteronucleus Correlation	187	(8)
Proton--Proton Correlation Through Space or Chemical Exchange	195	(4)
Carbon--Carbon Correlation	199	(2)
Higher Dimensions	201	(2)
Pulsed Field Gradients	203	(4)
Summary of Two-Dimensional Methods	207	(26)
Problems	208	(24)
Bibliography	232	(1)
Advanced Experimental Methods	233	(44)
One-Dimensional Techniques	233	(1)
T1 Measurements	233	(1)
13C Spectral Editing Experiments	234	(3)
The APT Experiment	235	(1)
The DEPT Experiment	236	(1)
NOE Experiments	237	(4)
The NOE Difference Experiment	238	(2)
The Double Pulsed Field Gradient Spin Echo-NOE Experiment	240	(1)
Two-Dimensional Techniques	240	(1)
Two-Dimensional NMR Data-Acquisition Parameters	241	(2)
Number of Data Points	241	(1)
Number of Time Increments	241	(1)
Spectral Widths	241	(1)
Acquisition Time	242	(1)
Transmitter Offset	242	(1)
Flip Angle	242	(1)
Relaxation Delay and Repetition Times	242	(1)
Receiver Gain	243	(1)
Number of Scans per Time Increment	243	(1)
Steady-State Scans	243	(1)
Two-Dimensional NMR Data-Processing Parameters	243	(7)
Weighting Functions	244	(2)
Zero Filling	246	(1)
Digital Resolution	246	(1)
Linear Prediction	247	(3)
Two-Dimensional NMR Data Display	250	(1)
Phasing and Zero Referencing	250	(1)
Symmetrization	250	(1)
Use of Cross Sections in Analysis	250	(1)
Two-Dimensional Techniques: The Experiments	251	(1)
Homonuclear Chemical-Shift Correlation Experiments Via Scalar Coupling	251	(6)
The COSY Family of Experiments	252	(4)
The TOCSY Experiment	256	(1)
Direct Heteronuclear Chemical-Shift Correlation Via Scalar Coupling	257	(5)
The HMQC Experiment	258	(1)
The HSQC Experiment	259	(2)
The HETCOR Experiment	261	(1)
Indirect Heteronuclear Chemical-Shift Correlation Via Scalar Coupling	262	(5)
The HMBC Experiment	262	(2)
The FLOCK Experiment	264	(2)
The HSQC-TOCSY Experiment	266	(1)
Homonuclear Chemical-Shift Correlation Via Dipolar Coupling	267	(3)
The NOESY Experiment	268	(1)
The ROESY Experiment	269	(1)
Miscellaneous 1D and 2D Experiments	270	(7)
The 1D TOCSY Experiment	270	(1)
The Multiplicity-Edited HSQC Experiment	271	(2)
The 2J, 3J-HMBC Experiment	273	(3)
Bibliography	276	(1)
Structural Elucidation: An Example	277	(18)
1H NMR Data	277	(2)
13C NMR Data	279	(1)
The DEPT Experiment	280	(1)
The HSQC Experiment	281	(1)
The COSY Experiment	282	(2)
The HMBC Experiment	284	(1)
General Molecular Assembly Strategy	284	(2)
A Specific Molecular Assembly Procedure	286	(4)
The NOESY Experiment	290	(5)
Appendix 1 Derivation of the NMR Equation	295	(2)
Appendix 2 The Bloch Equations	297	(5)
Appendix 3 Quantum Mechanical Treatment of the Two-Spin System	302	(10)
Appendix 4 Analysis of Second-Order, Three- and Four-Spin Systems by Inspection	312	(5)
Appendix 5 Relaxation	317	(5)
Appendix 6 Product-Operator Formalism and Coherence-Level Diagrams	322	(12)
Bibliography	333	(1)
Appendix 7 Stereochemical Considerations	334
A7-1 Homotopic Groups	335	(2)
A7-2 Enantiotopic Groups	337	(2)
A7-3 Diastereotopic Groups	339	(2)
Bibliography	341
Index	1

Excerpts

Nuclear magnetic resonance (NMR) has become the chemist's most general structural tool. It is one of the few techniques that may be applied to all three states of matter. Some spectra may be obtained from less than a microgram of material. In the early 1960s, spectra were taken crudely on strip-chart recorders. The field has since seen one major advance after another, culminating in the Nobel prizes awarded to Richard R. Ernst in 1991 and to Kurt Wuthrich in 2002. The very richness of the field, however, has made it intimidating to many users. How can they take full advantage of the power of the method when so much of the methodology seems to be highly technical, beyond the grasp of the casual user? This text was written to answer this question. The chapters provide an essentially nonmathematical introduction to the entire field, with emphasis on structural analysis.The early chapters introduce classical NMR spectroscopy. A thorough understanding of proton and carbon chemical shifts (Chapter 3) is required in order to initiate any analysis of spectra. The role of other nuclei is key to the examination of molecules containing various heteroatoms. An analysis of coupling constants (Chapter 4) provides information about stereochemistry and connectivity relationships between nuclei. The older concepts of chemical shifts and coupling constants are emphasized, because they provide the basis for the application of modern pulse sequences.Chapter 5 and 6 describe the basics of modern NMR spectroscopy. The phenomena of relaxation, of chemical dynamics, and of multiple resonance are considered thoroughly. One-dimensional multipulse sequences are explored to determine the number of protons attached to carbon atoms, to enhance spectral sensitivity, and to determine connectivities among carbon atoms. Concepts that have been considered advanced, but are now moving towards the routine, are examined, including phase cycling, composite pulses, pulsed field gradients, and shaped pulses. Two-dimensional methods represent the current apex of the field. We discuss a large number of these experiments. It is our intention to describe not only what the pulse sequences do, but also how they work, so that the user has a better grasp of the techniques.Two chapters are dedicated to experimental methodologies. Although many people are provided with spectra by expert technicians, increasing numbers of chemists must record spectra themselves. They must consider and optimize numerous experimental variables. These chapters address not only the basic parameters, such as spectral width and acquisition time, but also the parameters of more advanced techniques, such as spectral editing and twodimensional spectra.To summarize modern NMR spectroscopy, Chapter 8 carries out the total structural proof of a single complex natural product. This chapter illustrates the tactics and strategies of structure elucidation, from one-dimensional assignments to two-dimensional spectral correlations, culminating in stereochemical analysis based on Overhauser effects.The theory behind NMR not only is beautiful in itself, but also offers considerable insight into the methodology. Consequently, a series of appendices presents a full treatment of this theoretical underpinning, necessary to the physical or analytical chemist, but possibly still edifying to the synthetic organic or inorganic chemist.This text thus offers classical analysis of chemical shifts and coupling constants for both protons and other nuclei, modern multipulse and multidimensional methods, both explained and illustrated, experimental procedures and practical advice relative to the execution of NMR experiments, a chapter-long worked-out problem that illustrates the application of nearly all current methods to determine the structure and stereochemistry of a complex natural product, appendices containing the theoretical basis of