NMR and Chemistry: An introduction to the Fourier transform-multinuclear era

275 Pages·1983·6.22 MB·English

by  J. W. Akitt (auth.)

NMR and Chemistry
An introduction to the
Fourier transform-multinuclear era
NMR and Chemistry
An introduction to the
Fourier transform-multinuclear era
J. W.Akitt
School 0/ Chemistry
University 0/ Leeds
Second Edition
Springer-Science+Business Media, B.V.
Second edition 1983
© 1983 J. W. Akitt
Originally published by Chapman & Hall in 1983.
Softcover reprint ofthe hardcover 2nd edition 1983
ISBN 978-0-412-24010-2 ISBN 978-1-4899-3097-2 (eBook)
DOI 10.1007/978-1-4899-3097-2
This title is available in both hardbound and paperback editions. The
paperback edition is sold subject to the condition that it shall not, by
way of trade or otherwise, be lent, re-sold, hired out, or otherwise
circulated without the publisher's prior consent in any form of binding
or cover other than that in which it is published and without a similar
condition including this condition being imposed on the subsequent
purchaser.
All rights reserved. No part of this book may be reprinted, or
reproduced or utilized in any form or by any electronic mechanical or
other means, now known or hereafter invented, including photocopying
and recording, or in any information storage and retrieval system,
without permission in writing from the Publisher.
British Library Cataloguing in Publication Data Library of Congress Cataloging in Publication Data
Akitt, J. W. Akitt, J. W.
NMR and chemistry. - 2nd ed. NMR and chemistry.
1. Nuclear magnetic resonance spectroscopy Bibliography: p.
I. Title lncludes index.
538'.362 QC762 1. Nuclear magnetic resonance spectroscopy.
I. Title. 11. Title: N.M.R. and chemistry.
QD96.N8A37 1983 538'.362 83-1773
Contents
Preface to the fllst edition ix
Preface to ·the second edition xi
1 The theory of nuclear magnetization
1.1 The properties of the nucleus of an atom
1.2 The nucleus in a magnetic field 4
1.3 The so ur ce of the NMR signal 7
1.4 A basic NMR spectrometer 13
2 The magnetic field at the nucleus 16
2.1 Effects due to the moleeule 16
2.2 Effects due to unpaired electrons 24
2.3 The chemical shift 25
3 Intemuclear spin-spin coupling 29
3.1 The mutual effects of nuclear magnets on resonance
positions 29
3.2 The appearance of multiplets arising from spin-spin
coupling 32
3.3 Spin-spin coupling satellites 42
3.4 Second-Qrder effects 45
4 Nuclear magnetic relaxation and related phenomena 61
4.1 Relaxation processes in assemblies of nuclear spins 61
4.2 Relaxation, Brownian motion and sampie viscosity 64
4.3 Dipole-dipole relaxation 68
vi Contents
4.4 Electric quadrupole relaxation 68
4.5 Other relaxation mechanisms 75
4.6 The spectrometer output, its detection and resonance 76
line-shape
4.7 Measurement of Tl and T2 87
4.8 NMR spectra of dynarnic systems 91
5 Modern spectrometer systems 102
5.1 Time and frequency domains 102
5.2 The collection of data in the time domain 103
5.3 The Fourier transform 119
5.4 Manipulations in the frequency domain 124
5.5 Continuous wave (CW) spectroscopy 127
5.6 Time sharing spectrometers 128
5.7 A modern system 131
6 Thesample 132
6.1 Standardization 132
6.2 Solvent effects 135
7 Multiple resonance experiments 141
7.1 Double resonance and spin-spin coupling 142
7.2 Through-space coupling via the relaxation field 151
7.3 Selective population inversion 161
7.4 Double resonance and exchange coupling 161
8 Some new and exciting techniques in NMR 165
8.1 Two-dimensional NMR 165
8.2 Whole body imaging 169
8.3 In vivo biological investigations 170
8.4 High resolution solid state NMR 172
8.5 High pressure NMR 183
9 Some examples of the use of NMR in chemistry 187
Part A Proton and carbon spectroscopy 187
9.1 The determination of the structures of organic
molecules using proton spectra 187
9.2 Determination of the structures of organic molecules
using proton and carbon spectra together 189
Contents vii
9.3 Determination ofthe conforrnations of moleeules 201
9.4 Proton homonuclear double resonance studies 204
9.5 The determination of the structures of transition
metal complexes 209
9.6 Variable temperature studies of so me dynamic systems 214
9.7 Lanthanide-induced shifts - shift reagents 220
9.8 Significance of carbon-13 relaxation times 224
Part B The use of the other nuclear resonances 225
9.9 Main group I 225
9.10 Main group 11 228
9.11 Main group III 228
9.12 Maingroup V 235
9.13 Main group VI 243
9.14 Main group VII 247
Further exercises 250
Answers 255
Bibliography 257
Index 259
Preface to the First Edition
About 20 years have elapsed since chemists started to take an interest
in nuc1ear magnetic resonance spectroscopy. In the intervening period it
has proved to be a very powerful and informative branch of spectroscopy,
so much so that today most research groups have access to one or more
spectrometers and the practising chemist can expect constantly to
encounter references to the technique. There is a considerable number
of textbooks available on the subject but these are invariably written
primarily either for the specialist or for the graduate student who is
starting to use the technique in his research. The author has, however,
always feIt that a place existed for a non-specialist text written for the
undergraduate student giving an introduction to the subject which
embraced the whole NMR scene and which would serve as a basis for
later specialisation in any ofthe three main branches of chemistry.
With this in mind the book has been written in two sections. The
first covers the theory using a straight forward non-mathematical
approach which nevertheless introduces some of the most modern
descriptions of the various phenomena. The text is illustrated by
specific examples where necessary. The second section is devoted to
showing how the technique is used and gives some more complex
examples illustrating for instance its use for structure determination
and for measurements of reaction rates and mechanisrns. A few problems
have been inc1uded but the main purpose of the book is to demonstrate
the many and varied present uses of NMR rat her than to teach the
student how to analyse a spectrum in detail. This is done best if it is
done concurrently with a student's own research.
I am indebted to Dr K. D. Crosbie, Professor N. N. Greenwood,
Dr B. E. Mann, and to Professor D. H. Whiffen who read and criticised the
x Pre/ace to the first edition
manuscript and to many former colleagues at Newcastle-upon-Tyne
for encouragement and for some of the examples used in the text. I also
give grateful acknowledgement to Varian Associates Ltd. for per mission
to reproduced the spectra in Figs 15, 17,26,27,66 and 75 and to
Bruker-Spectrospin Ltd. for per mission to reproduce the spectra in
Figs 49, SO, 63, 64 and 75.
Leeds, J.W.A.
January, 1972
Preface to the Second Edition
It is just ten years since I wrote the preface to the fIrst edition of this
book. The intervening decade has, however, seen such an explosive
development of the subject that it haS changed almost out of all
recognition. Certainly some material has had to be completely replaced
by new and the text has had to be extensively rewritten to accommodate
current concepts. The fIrst edition contained a mention of Fourier
transform techniques, and of superconducting magnets, and these two
fIelds have both developed extremely rapidly because it was realized
that they would make possible some real advances in chemical research.
The new 13C spectroscopy of organic molecu1es on the one hand
increased the scope of the technique for structural determination, and
high fIeld proton spectroscopy on the other enabled the problem of
the solution structure of large, biologically important molecu1es to be
tackled. It was also increasingly realized that the Fourier transform
pu1se techniques allowed precise manipu1ation of nuc1ear spins so that
many different new relaxation or double resonance experiments
becarne possible. Such advances have also proved to be informative
when applied to the less popular nuc1ei and so multinuclear flexibility
was introduced into the new, powerful NMR spectrometers, which can,
in principle, carry out most likely experiments with every magnetically
active nuc1eus in the periodic table.
Development has, however, not stopped here. The dimcu1t field of
the high resolution study of solid sampies is being successfu1ly ploughed;
the separation of shift and coupling parameters in a two-dimensional
experiment is now possible and the biologists have started to look at
somewhat unusual sampies such as anaesthetized live rats.
One particularly interesting development which is being vigorously