Nuclear Magnetic Resonance Spectroscopy

Published by anjer | Filed under Physics

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.

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 NMR, including the most modern approach that uses product operators and coherence-level diagrams, and — extensive problems throughout the book.











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