# Book Review Organomagnesium Methods in Organic Synthesis. (Series Best Synthetic Methods.) By B. J. Wakefield

код для вставкиСкачать~~~ ~~ BOOKS ~ one of the pioneers in the development and application of the theory of crossing potential curves, usually called the valence bond configurational mixing (VBCM) theory or the curve-crossing model. The book contains ten chapters which are grouped under three main sections: “Theoretical Principles”, “Principles of Physical Organic Chemistry”, and “Reaction Types”. The first section introduces some basic concepts of molecular quantum mechanics. Here the author avoids using mathematical formalism as far as possible. The comparison between the molecular orbital and valence bond theories is well presented and instructive. The fourth chapter starts from simple potential energy curves and develops the theory to discuss reaction profiles using the VBCM method. The three most important “ingredients” of the VBCM theory are explained here, namely the initial excitation energy C, the fraction fact0r.f; and the resonance energy B. Chapter 5 continues this theme with scarcely a perceptible break, explaining a number of well-established reactivity concepts such as the Hammond postulate, the Bell-EvansPolanyi principle, and the Marcus theory. Both these chapters make easy reading as the arguments follow a clear sequence. However, they could have been improved by including a little more detail, especially in the treatment of the Marcus theory. Chapter 6 discusses empirical structurereactivity relationships that are not based on a theoretical model, such as the Hammett and Brernsted relationships. In Chapter 7 the author provides the reader with all the theoretical tools needed to apply the VBCM theory qualitatively: the excitation energies, electron affinities, and ionization potentials. Chapter 8 then deals with solvent effects on reaction rates, describing various classical procedures for quantifying such effects, and finally considering solvent effects in terms of the VBCM theory. The third section of the book is entirely devoted to applications of the VBCM theory to various types of reactions. In accordance with the historical development of the theory it is natural that the greatest emphasis is given to nucleophilic substitution reactions and to general considerations regarding the reactivity of nucleophiles. The last chapter describes recent work by the author on the reactivity of free radicals and carbenes and the application of the VBCM model to pericyclic reactions. The author writes in an excellent and didactically clear style, both in explaining fundamental concepts and in discussing the many well-chosen examples; thus the A f i g c ~Chem. . In[. Ed. Engl. 1996, 35. No. 16 central features of the VBCM theory come out especially clearly. Pross confines the discussion to considerations of energy level diagrams and variations in the initial excitation energy, and thus all aspects are treated qualitatively and in a comparative way. This makes the book especially suitable for the readership intended by the author, defined as “advanced undergraduate and graduate students as well as researchers in organic chemistry”. The quantitative application of the VBCM theory has already been treated in a monograph by S. Shaik et al. published in 1992 and reviewed in this journal (Angew. Chern. 1993, 105,1277; Angew. Chem. Int. Ed. Engl. 1993, 32, 1106). Perhaps the only complaint about this excellent introduction is that nearly all the publications on the VBCM theory cited here originate either from the author himself or from S. Shaik. Proposed extensions to the VBCM theory, such as those discussed in the literature by V. Parker, are not mentioned. Also the chosen examples are rather onesided, in that they illustrate the scope but not the limitations of the VBCM theory. These become especially evident in reactions with very low energy barriers, such as those between nucleophiles and radical cations, and generally in bimolecular reactions where intermolecular attractive forces come into play. Hendrik Zipse Institut fur Organische Chemie der Technischen Universitat Berlin Berlin (Germany) Organomagnesium Methods in Organic Synthesis. (Series: Best Synthetic Methods.) By B. J. Wakefeld. Academic Press, London, 1995. 249 pp., hardcover E 50.00.-ISBN 0-1 2-730945-4 Like the other volumes of this series, the book reviewed here is designed to inform synthetic organic chemists about the capabilities, advantages, and limitations of a particular class of synthetic methods from a practical standpoint. The approach is based not only on describing many examples from the literature but also on giving detailed laboratory procedures for carrying out the preparations. From this the reader can quickly gain a comprehensive picture of the reaction conditions, the techniques used, and the work-up procedures. The first of the 16 chapters in this volume deals with general aspects, beginning with a fairly brief account of the structures and reactive properties of organo- Q VCH Verlagsgesellschafr m b H , 1)-69451 Weinheim,1996 magnesium compounds, then discussing in more detail the methods for handling and using them. The author discusses the different solvents used and describes the techniques for working in an inert environment and performing titrations. This is followed by a chapter of more than fifty pages on the preparation of organomagnesium compounds, including detailed descriptions of 25 laboratory procedures. As well as methods based on activation of magnesium metal, this includes routes that start from other organomagnesium or organolithium compounds, and ligand exchange reactions. The chapters that follow describe applications of organomagnesium compounds in synthesis. The list includes addition reactions of alkenes, alkynes, carbon-nitrogen multiple bonds, carbony1 compounds, and thiocarbonyl compounds, followed by substitutions at carbon atoms, reactions yielding carbenes and arynes, reactions with acidic compounds, methods for forming carbon-nitrogen, carbon-oxygen, carbon-sulfur, carbon - selenium, carbon - tellurium, and carbon-halogen bonds, and methods for synthesizing organoboron. organophosphorus, organosilicon, and various organometallic compounds. Reaction mechanisms are also explained in some cases, but the emphasis remains firmly on practical synthetic applications. The great value of the book lies in its presentation of the broad scope of applications of organomagnesium compounds, in the wealth of examples that are described, and in the detailed descriptions of experimental procedures. The examples from the literature are closely integrated with the selected laboratory recipes. In addition there are tables referring the reader to other published examples. Unfortunately the laboratory procedures are not easily distinguished at a glance from the main text, which would have made for easier reading. However, a very positive aspect of these descriptions is the attention to the detailed needs of the user, including not only valuable advice about special points concerning the reactions, but also about possible difficulties, such as side-reactions that may occur, or the extent to which the reaction is or is not compatible with the presence of certain functional groups. The coverage of the literature is very thorough, including some references as recent as 1994. The inclusion of the laboratory recipes in the list of contents is a useful aid, but it would also have been helpful to provide in addition a “graphic abstract” for quick access to the information. To summarize, this should not be regarded as a textbook (nor is it intended to 0570-083319613S16-1867 S IS.OOi 2S!U 1867 BOOKS be), but it can be thoroughly recommended as a very useful reference source for libraries and for all chemists wishing to use organomagnesium compounds in synthetic work. Sabine Laschat Organisch-chemisches Institut der Universitlt Miinster (Germany) Multidimensional NMR in Liquids. Basic Principles and Experimental Methods. By F: J. M. van der Ven. VCH Verlagsgesellschaft, Weinheim/ VCH Publishers, New York, 1995. 400 pp., hardcover DM 85.00.ISBN 1-56081-665-1 This book is an up-to-date introduction to multidimensional N M R spectroscopy as applied to biomolecules. It has been written for chemists, biochemists, and biologists interested in problems of molecular structure, who wish to gain a deeper understanding of N M R spectroscopy and have the necessary background in physical chemistry. The mathematical and physical fundamentals of N M R spectroscopy are presented in an exemplary way, without assuming a great deal of previous knowledge. The theoretical tools introduced are later used repeatedly and consistently in the applications part of the book to describe pulsed N M R experiments, thus enabling the reader to relate them directly to practical situations. A particular peptide (His-Val-Tyr) and a protein (the Pf3-DNA binding protein) appear frequently thoughout the book as standard example molecules to illustrate and explain the various N M R experiments used in determining the structures of biomolecules. The first of the six chapters begins by explaining the vector formalism used for N M R spectroscopy, and basic concepts such as radiofrequency pulses, the rotating frame, off-resonance effects, the free precession of a spin, and Bloch-Siegert effects. This is followed by a more technically-orientated description of the main components of an N M R spectrometer and of data processing methods. At the end of this chapter the author introduces the density matrix, and discusses the relationship between the quantum-mechanical description of a spin in Liouville space and the vector formalism. Chapter 2 is concerned with the fundamental properties of multi-spin systems, introducing the scalar coupling and the chemical shift as the dominant parameters. The role of these parameters in the development of a spin system as a func1868 tion of time is described using the product operator formalism, according to the theory formulated by the author simultaneously with the work of Serrensen, Bodenhausen, and Ernst. The product operator formalism using Cartesian basis operators plays a central role in the description of N M R experiments throughout the book. The phenomenological description of relaxation in the product operator formalism is briefly discussed. The chapter ends by introducing and explaining the most important terms in the spin Hamiltonian operator (the chemical shift, the spin-spin coupling, and the interaction with the r.f. field). Chapter 3 shows how a one-dimensional N M R experiment can be described as an assembly of modules in which the basic building blocks are a 90’ pulse and a 180’ pulse. These can produce many different effects, such as refocussing of the precessing spins, modulation of the J-coupling, the appearance of a spin-echo, etc. This chapter also describes experiments for measuring the longitudinal and transverse relaxation times and for calibrating pulses, and various types of experiments using heteronuclear detection, such as the wellknown INEPT and DEPT procedures. Lastly some more complicated building blocks are described, such as “composite” pulses and decoupling sequences. Because ever more new and improved pulse sequences are continually being introduced, the author is here less concerned with evaluating the existing sequences than with showing the reader what factors should be considered in assessing the usefulness of any newly developed pulse or decoupling sequence. Chapter 4 is concerned with two-dimensional N M R spectroscopy. The first 60 pages of the chapter are devoted to the COSY experiment, which was the earliest type of 2D experiment and is the simplest. The underlying philosophy here may have been that once one has understood the. COSY experiment one has the key to the whole of 2D N M R spectroscopy. This method serves as an example for explaining various tools of 2D N M R spectroscopy, including phase cycles, field gradients, the BIRD pulse sequence, sign differentiation in indirect dimensions (TPPI, states, states-TPPI, etc.), multiquantum filters, and small flip-angle pulses. The other basic mixing schemes for magnetization transfer are then described: Hartmann-Hahn mixing, NOESY via the nuclear Overhauser effect, then ROESY and TOCSY. This is followed by a discussion of heteronuclear correlation experiments with proton detection (HSQC, HMQC, HMBC). Correlation experi- Q VCH Verlug.~gesells~lIufft m h H , 0-69451 Wcinhcim, 1996 ments with heteronuclear detection are now scarcely used at all for applications to biomolecules, and are therefore not discussed further. The chapter ends with a detailed discussion of “coherence order pathways”, which form the basis for the design of phase cycles and pulsed gradient sequences for suppressing unwanted signals. Chapter 5 moves on to n-dimensional N M R spectroscopy. Many different experiments of this kind have been developed during the last six years. The author describes the most useful of these, using the product operator formalism. These are arranged in order of the complexity of the pulse sequences rather than according to the spectral or chemical information that they yield. A number of important experiments are described, including 3D and 4 D versions of NOESY-HMQC, HCCH-TOCSY, HNCO, HN(CO)CA, and CBCA(C0)NH. Those treated here are only a selection of the many different methods that can be applied to tasks such as determining the structure of a protein. However, the author clearly explains the principles on which the sequences are based, so as to enable the reader to understand the original publications and to evaluate new sequences. The spectral information yielded by these methods plays only a secondary role in the discussions. The final chapter is devoted to relaxation. This is undoubtedly the most difficult topic to treat. The author first sets out the fundamental principles of relaxation using the example of stochastic fields, leading to simple derivations of the most important mathematical expressions for dipolar relaxation (NOE, ROE, T I , and T,). He then goes on to derive a formalism for relaxation in terms of the density matrix. After a brief resume of the Wangsness-Bloch-Redfield relaxation theory he then calculates the double commutators needed to describe the most important magnetic interactions, namely the dipolar relaxation and the chemical shift anisotropy, and the cross-correlation between these interactions. In contrast to the previous chapters, this chapter on relaxation devotes relatively little attention to relating the results to spectroscopic practice. However, the bibliography for this chapter includes references to review articles and other publications describing relevant experiments and the types of information that they can give about the dynamic structures of biomolecules. The book can be thoroughly recommended for everyone who wishes to gain a deeper understanding of the applications of N M R spectroscopy to biomolecules in solution. It is unrivalled in its up-to-date aS70-a833/96/3516-1868 $ 15.00f .2S/O Angeu. Chem. I n ! . Ed. Engl. 1996, 35, N o . 16

1/--страниц