Nuclear resonances are affected by a variety of weak interactions between the nuclei and the electrons of molecules, between nuclei within the molecules and between nuclei in neighbouring molecules. If these interactions can be disentangled and interpreted, they are found to contain...
Nuclear resonances are affected by a variety of weak interactions between the nuclei and the electrons of molecules, between nuclei within the molecules and between nuclei in neighbouring molecules. If these interactions can be disentangled and interpreted, they are found to contain an extraordinarily rich mine of information about the structures and conformations of the molecules of the sample, about interactions between molecules and about molecular motion.
All this is made possible by the very long relaxation times that characterise NMR spectra of spin Vi nuclei in mobile liquids; line widths of 0.1 Hz or less at 500 MHz are by no means uncommon. This means that even resonances which lie very close together can be resolved.
High resolution spectra, even of molecules of modest molecular weight, are therefore often quite complicated, but because the interactions are weak, cross terms are not very important if the measurements are made in strong magnetic fields, and the spectra are relatively easy to interpret. It is not surprising, therefore, that high resolution NMR has become such an indispensable tool for the organic chemist.
As the size of the sample molecules becomes greater, the complexity of the NMR spectra increases rapidly, lines overlap, and their interpretation becomes more difficult. At this stage much more sophisticated sequences of experiments must be made, the analysis of which can be technically demanding. Here the organic chemist is faced with a dilemma. How much effort should he or she invest in grappling with the not inconsiderable technicalities of the very powerful NMR techniques now available? It is certain that without some understanding of these methods he may not even realise how NMR can help him solve his particular problems, and even if he thinks help is available, he must beware of using NMR as an imperfectly understood black box.
Most organic chemists to-day need to understand what NMR can do for them, and in this book Dr Derome sets out the principles and provides a practical guide to the use of NMR spectroscopy in terms accessible to organic chemists; it is a long journey but one which will be well worth while. The reader who perseveres with the book will be considerably enlightened. I hope the reader will also be sufficiently fired by the enthusiasm running through the text to read at some later stage the further references provided and achieve still greater depths of understanding of these elegant experiments.
Sir Rex Richards, FRS University of Oxford
Cím: Modern NMR Techniques for Chemistry Research [antikvár]