Structure Elucidation by Modern NMR

Transcription

1 Structure Elucidation by Modern NMR

2 H. Duddeck, W Dietrich Structure Elucidation by ModemNMR A Workbook With a Preface by J. B. Stothers

3 Prof. Dr. H. Duddeck Dr. W Dietrich FakulHit flir Chemie Ruhr-UniversiUit Bochum Postfach Bochum, FRG CIP-Titelaufnahme der Deutschen Bibliothek Duddeck, Helmut: Structure elucidation by modern NMR : a workbook / H. Duddeck ; W. Dietrich. With a pref. by 1. B. Stothers. - Darmstadt: SteinkoptT ; New York: Springer, 1989 Dt. Ausg. u. d. T.: Duddeck, Helmut: StrukturaufkJiirung mit moderner NMR-Spektroskopie ISBN-13: e-isbn-13: DOl: / NE: Dietrich, Wolfgang: This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broad-casting, reproduction on microfilms or in other ways, and storage in data banks. Duplication ofthis publication or parts thereofis only permitted under the provisions of the German Copyright Law of September 9, 1965, in its version of June 24, 1985, and a copyright fee must always be paid. Violations fall under the prosecution act of the German Copyright Law. Copyright 1989 by Dr. Dietrich Steinkopff Verlag GmbH & Co. KG, Darmstadt Chemist Editor: Heidrun Sauer - Copy Editing: Marilyn Salmansohn - Production: Heinz 1. Schiifer The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.

4 Foreword For several years we have been organizing seminars and workshops on the application of modem oneand two-dimensional NMR methods at the faculty of chemistry in the Ruhr-University Bochum, FRG, and elsewhere, addressing researchers and graduate students who work in the field of organic and natural products chemistry. In 1987, we wrote a workbook (StrukturaufkUirung mit modemer NMR-Spektroskopie, Steinkopff, Darmstadt, FRG, 1988) in German language based on our experience in these courses. Many of the exercises described therein have been used in such courses and some of them have been shaped by the participants to a great extent. The response of readers and discussions with colleagues from many countries encouraged us to produce an English translation in order to make the book accessible to a wider audience. Moreover, the content has been increased from 20 exercise examples in the German, to 23 in the English version. This book could not have been written in the present form without the help of a number of colleagues and, therefore, we acknowledge gratefully the generous supply of samples from and useful discussions with B. Abegaz (Addis Ababa, Ethiopia), U.H. Brinker (Bingham, New York, USA), E. Dagne (Addis Ababa, Ethiopia), M. Gonzalez-Sierra (Rosario, Argentina), J. Harangi (Debrecen, Hungary), SA Khalid (Khartoum, Sudan), A. Levai (Debrecen, Hungary), MA McKervey (Cork, Ireland), M. Michalska (Lodz,Poland), EA Ruveda (Rosario, Argentina), G. Snatzke (Bochum, FRG), L. Szihigyi (Debrecen, Hungary), G. T6th (Budapest, Hungary), P. Welzel (Bochum, FRG), J. Wicha (Warsaw, Poland) und K. Wieghardt (Bochum, West Germany). We also thank M. H. Kuhne, Mrs. D. Rosenbaum, M. Gartmann and Mrs. E. Sauerbier for their committed cooperation, their assistance in the measurements, and preparation of figures. Inspite of painstaking efforts mistakes can hardly be avoided. We are always grateful for any response from readers to correct or improve the text. If we have been successful in conveying an impression of the wealth of information offered by modem NMR,then the book has satisfied its goal. Bochum, FRG, February 1989 Helmut Duddeck Wolfgang Dietrich

5 Preface (translated from the original German edition) The history of nuclear magnetic resonance (NMR) is characterized by a number of significant technical achievements. The latest progressive step is the invention of the two-dimensional NMR spectroscopy, which, with its concept of time evolution, has given rise to the development of numerous, also one-dimensional, techniques. It is fortunate that, at the same time, cryomagnetic technology has reached a high point in its development. Consequently, high field NMR spectrometers are now standard equipment for university chemistry departments and industrial laboratories, so that larger and more complex molecules can be investigated with respect to their structure, dynamics and reactivity. It is not an exaggeration to say that applied high-resolution NMR spectroscopy has been revolutionized by the two-dimensional methodology. Previously, measurement of the NMR spectrum was confined to standard experiments involving spin excitation and signal registration; little allowance was made for variation. Now a number of experiments with different objectives and various levels of sophistication are available, often making it difficult to decide which of these experiments can reliably supply the desired information in as short a recording time as possible. This problem can only be solved by chemists who are well versed in the new techniques. It is therefore fortuitous that Helmut Duddeck and Wolfgang Dietrich have used their experience gained in the NMR laboratory of a large chemistry department to fill the gap between spectroscopists and chemists working synthetically. In this volume they tell us about modem one- and two-dimensional NMR experiments on molecular structure and pertinent NMR analysis, and in so doing, arouse interest in such experiments in general. Moreover, they elucidate the potential and the limits of these new techniques. Thus, they have created a workbook that concentrates on the essential methods already approved in practice. The book follows the pragmatic tradition of the American textbook, which regards the "Aha! experience" gained by working with practical examples as being as important as the study of consistent, theory-based treatments. The book contains excellent illustrations and is expected to find a broad resonance in introductory courses and lectures on "2D-NMR." It is hoped that this workbook will be successful, and it is heartily recommended to all chemists as an introduction to the practical application of modem NMR spectroscopy. Siegen, FRG, February 1989 H. Gunther

6 Preface After the flrst spectrometers became generally available the application of high-resolution nuclear magnetic resonance (NMR) spectroscopy to molecular structural analysis rapidly became a primary endeavor of organic chemists. The growth and development of NMR has been characterized by a series of major technological advances. In the 1950s single resonance 1 H experiments prevailed and provided basic information for a given sample on the numbers of nonequivalent nuclei, their relative shieldings, and their spin-coupled neighbors. In the early 1960s, multiple resonance techniques were introduced which permitted the extraction of more detailed information and also gave evidence of the potential of 13C MR-studies. In the late 1960s, Fourier transform (FT) methods dramatically improved sensitivity, so that 13C spectra could be obtained routinely. The FT technique also rendered measurements of time-dependent phenomena much more accessible. Equally important, the FT approach led to the notion of utilization of a second dimension, the potential of which was clearly recognized in the late 1970s. Through the 1980s, the implementation of these experiments has spawned new powerful methods for eliciting structural information through establishing correlations between different nuclear types and also leading to new, useful one-dimensional methods. Over this time span, advances in magnet technology provided higher and higher applied flelds, increasing the sensitivity of the experiments and permitting detailed study of larger and more complex molecules. The modem high-resolution NMR spectrometer is a powerful, sophisticated system capable of providing a veritable mine of information, perhaps the most important single tool available for structural analysis. This series of advances has perforce raised the level of sophistication required for the analysis and interpretation of the results and, while many practicing organic chemists are undoubtedly aware of instrumental capabilities, many lack direct experience with their application to real problems. Some expert guidance in the choice of speciflc experiments to supply the required data most reliably and, preferably, most efficiently will be welcome. Helmut Duddeck and Wolfgang Dietrich speciflcally address this need in the present volume. From experience gained in their own research and from organizing seminars and workshops, they have assembled 23 typical cases in this workbook to illustrate applications of modem NMR to organic structural analysis. Following clear, brief descriptions of the basic techniques, accompanied by some excellent illustrations, these cases are presented as problems to be solved by the reader. For the neophyte, strategies for approaching each case are outlined and, in the flnal chapter, detailed discussions of solutions for each are presented. This workbook is an excellent introduction to the practical application of modem NMR spectroscopy to structural problems and is highly recommended to all who seek guidance in the utilization of two-dimensional NMR. London, Canada, November 1988 J.B. Stathers

7 Contents Foreword Preface Preface 1. Introduction Methodology High Magnetic Fields One-dimensional 13 C NMR Spectra (DEPT) NOE Difference Spectra H, 1 H Correlated (H,H COSY) 2D NMR Spectra H, 13C Correlated (H,C COSY)2D NMR Spectra COLOC Spectra D 13C,13C (C,C COSY) INADEQUATE Spectra Exercises....' Strategies S. Solutions Compound Index

8 To Giinther Snatzke who teaches to love the architecture of three-dimensional molecular structures.