Solving problems with NMR spectroscopy 2nd ed

Solving Problems with NMR Spectroscopy Second Edition Atta-ur-Rahman International Center for Chemical and Biological Sciences (H E J Research Institute of Chemistry and Dr Panjwani Center for Molecular Medicine and Drug Research), University of Karachi, Karachi-75270, Pakistan Muhammad Iqbal Choudhary International Center for Chemical and Biological Sciences (H E J Research Institute of Chemistry and Dr Panjwani Center for Molecular Medicine and Drug Research), University of Karachi, Karachi-75270, Pakistan Atia-tul-Wahab Dr Panjwani Center for Molecular Medicine and Drug Research (International Center for Chemical and Biological Sciences), University of Karachi, Karachi-75270, Pakistan AMSTERDAM • BOSTON • HEIDELBERG • LONDON NEW YORK • OXFORD • PARIS • SAN DIEGO SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Academic Press is an Imprint of Elsevier Academic Press is an imprint of Elsevier 125, London Wall, EC2Y 5AS, UK 525 B Street, Suite 1800, San Diego, CA 92101-4495, USA 225 Wyman Street, Waltham, MA 02451, USA The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK Copyright © 2016, 1996 Elsevier Inc All rights reserved No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein) Notices Knowledge and best practice in this field are constantly changing As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 978-0-12-411589-7 For information on all Academic Press publications visit our website at http://store.elsevier.com/ Foreword The second edition of the book Solving Problems with NMR Spectroscopy is aimed to strengthen the understanding of how an NMR spectrometer functions This revised version of the book takes the same problem-solving approach as the highly praised first edition, published in 1996 The book focuses on describing the basic principles of NMR spectroscopy and explains in detail the functioning of an NMR spectrometer The optimum use of this powerful technique is introduced step by step, and common problems encountered by the practitioners and users of NMR spectroscopy are described in an easy-to-understand manner The real strength of the book is its highly practical approach in describing both the concepts and applications of NMR spectroscopy The second edition introduces a number of new topics, including developments in NMR hardware, such as cryogenically cooled probes, new probeheads, high-field magnets, and DNP–NMR, as well as innovative pulse sequences, such as DOSY, concatenated NMR techniques, and PANSY Particularly interesting is a new chapter on sensitivity issues in NMR spectroscopy and their currently available applications, which have driven most of the developments in this field Another chapter on recent developments in NMR spectroscopy updates the readers about the changing landscape in this field Over 180 penetrating problems and their well-described solutions help to reinforce and test the understanding of the readers about various aspects of modern NMR spectroscopy Many of these problems focus on developing the interpretation skills of the readers in various types of NMR spectra toward structure determination The use of color printing and improved figures enhance the readability of the text The revised edition of Solving Problems with NMR Spectroscopy by Attaur-Rahman, M Iqbal Choudhary, and Atia-tul-Wahab is certainly a very useful addition to the NMR literature I am confident that the book will receive wide appreciation both from students as well as professionals Professor Dr Richard R Ernst Nobel Prize in Chemistry, 1991 Zurich, 2015 xi Chapter The Basics of Modern NMR Spectroscopy Chapter Outline 1.1 What Is NMR? 1.1.1 The Birth of a Signal 1.2 Instrumentation 1.2.1 The Magnet 1.2.2 The Probe 1.2.3 Probe Tuning 1.2.4 Shimming 10 11 14 17 1.2.5 Deuterium Lock 1.2.6 Referencing NMR Spectra 1.2.7 NMR Sample Tubes Solutions to Problems References 22 22 23 25 33 1.1  WHAT IS NMR? Nuclear magnetic resonance (NMR) spectroscopy is the study of molecules by recording the interaction of radiofrequency (Rf ) electromagnetic radiations with the nuclei of molecules placed in a strong magnetic field Zeeman first observed the strange behavior of certain nuclei when subjected to a strong magnetic field at the end of the nineteenth century, but practical use of the so-called “Zeeman effect” was made only in the 1950s when NMR spectrometers became commercially available Like all other spectroscopic techniques, NMR spectroscopy involves the interaction of the material being examined with electromagnetic radiation Why we use the word “electromagnetic radiation”? This is so because each ray of light (or any other type of electromagnetic radiation) can be considered to be a sine wave that is made up of two mutually perpendicular sine waves that are exactly in phase with each other, i.e., their maxima and minima occur at exactly the same point of line One of these two sine waves represents an oscillatory electric field, while the second wave (that oscillates in a plane perpendicular to the first wave) represents an oscillating magnetic field – hence the term “electromagnetic” radiation Cosmic rays, which have a very high frequency (and a short wavelength), fall at the highest energy end of the known electromagnetic spectrum and involve frequencies greater than 3 × 1020 Hz Radiofrequency (Rf ) radiation, which is Solving Problems with NMR Spectroscopy http://dx.doi.org/10.1016/B978-0-12-411589-7.00001-2 Copyright © 2016 Elsevier Inc All rights reserved Solving Problems with NMR Spectroscopy TABLE 1.1 The Electromagnetic Spectrum Radiation Wavelength (nm) l Frequency (Hz)  Energy (kJ mol−1) 20 >3 × 10 >1.2 × 108 Cosmic rays