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Although it was shown very early [1] that the isotope 29Si is very valuable for NMR research, severe technical difficulties had to be overcome before silicon spectra could be recorded. This was due to the low sensitivity of the isotope resulting from its low gyro magnetic ratio, its low abundance and the rather long relaxation times. The introduction of the Fourier-Transform-Technique (FT-NMR) helped to surmount most of these problems, with the result, that more and more papers concerning silicon NMR appear. Thus, it seems now that most of the salient features of 29Si-NMR are known today. Some resume of the state of the art of 29Si_NMR have been reported [1-4]. Although the theory of 29Si-NMR is not yet understood beyond the basic features, it promises to be of value mainly for two reasons: 1. Silicon is strategically located in the Periodic Table of the elements between the elements carbon, aluminum and phosphorus. For an unified theory of chemical shifts and coupling constants of the heavier elements silicon NMR values will be important. 2. The normal coordination number of silicon is four. If the current view of the chemical shifts of the heavier elements is correct, then the paramagnetic part is dominant for the measured shift data. Two of the parameters used for the calcu lation of the paramagnetic part are bond orders and angles. Bond angles are rare ly determined experimentally with high precision.
Although it was shown very early [1] that the isotope 29Si is very valuable for NMR research, severe technical difficulties had to be overcome before silicon spectra could be recorded. This was due to the low sensitivity of the isotope resulting from its low gyro magnetic ratio, its low abundance and the rather long relaxation times. The introduction of the Fourier-Transform-Technique (FT-NMR) helped to surmount most of these problems, with the result, that more and more papers concerning silicon NMR appear. Thus, it seems now that most of the salient features of 29Si-NMR are known today. Some resume of the state of the art of 29Si_NMR have been reported [1-4]. Although the theory of 29Si-NMR is not yet understood beyond the basic features, it promises to be of value mainly for two reasons: 1. Silicon is strategically located in the Periodic Table of the elements between the elements carbon, aluminum and phosphorus. For an unified theory of chemical shifts and coupling constants of the heavier elements silicon NMR values will be important. 2. The normal coordination number of silicon is four. If the current view of the chemical shifts of the heavier elements is correct, then the paramagnetic part is dominant for the measured shift data. Two of the parameters used for the calcu lation of the paramagnetic part are bond orders and angles. Bond angles are rare ly determined experimentally with high precision.
Although it was shown very early [1] that the isotope 29Si is very valuable for NMR research, severe technical difficulties had to be overcome before silicon spectra could be recorded. This was due to the low sensitivity of the isotope resulting from its low gyro magnetic ratio, its low abundance and the rather long relaxation times. The introduction of the Fourier-Transform-Technique (FT-NMR) helped to surmount most of these problems, with the result, that more and more papers concerning silicon NMR appear. Thus, it seems now that most of the salient features of 29Si-NMR are known today. Some resume of the state of the art of 29Si_NMR have been reported [1-4]. Although the theory of 29Si-NMR is not yet understood beyond the basic features, it promises to be of value mainly for two reasons: 1. Silicon is strategically located in the Periodic Table of the elements between the elements carbon, aluminum and phosphorus. For an unified theory of chemical shifts and coupling constants of the heavier elements silicon NMR values will be important. 2. The normal coordination number of silicon is four. If the current view of the chemical shifts of the heavier elements is correct, then the paramagnetic part is dominant for the measured shift data. Two of the parameters used for the calcu lation of the paramagnetic part are bond orders and angles. Bond angles are rare ly determined experimentally with high precision.
This book provides a comprehensive review of the application of 17O NMR spectroscopy to organic chemistry. Topics include the theoretical aspects of chemical shift, quadrupolar and J coupling; 17O enrichment; the effect of steric interactions on 17O chemical shifts of functional groups in flexible and rigid systems; the application of 17O NMR spectroscopy to hydrogen bonding investigations; mechanistic problems in organic and bioorganic chemistry; and 17O NMR spectroscopy of oxygen monocoordinated to carbon in alcohols, ethers, and derivatives. Recent results that show correlations between molecular geometry, determined by X-ray studies and estimated by molecular mechanics calculations, and 17O chemical shifts are also covered. 17O Spectroscopy in Organic Chemistry provides important reference information for organic chemists and other scientists interested in 17O NMR spectroscopy as a tool for obtaining new structural and chemical data about organic molecules.
Noncrystalline (NC) solids, as is well known, lack the long range order of crystals. Accordingly, they exhibit scattering, e.g., x-ray, electron, and neutron, but not the diffraction patterns characteristic of crystals. The intensity distributions from NC solids are usually transformed into radial distribution functions (RDF), but the interpretation of the RDF's is not unique. The lack of long-range order, and the non-uniqueness of the structural interpretation, have constituted the main obstacles to the usual solid state physics approach which has been so successful in dealing with crystals. As a corrolary, questions of local order and structure have frequently been de-emphasized. This monograph contains a collection of chapters many of which emphasize local-structure and chemical bonding as opposed to long-range order. Most of the chapters were chosen from talks given at the international symposium, "Structure and Bonding in Noncrystalline Solids," held in Reston, Virginia in May of 1983. Other chapters, however, were simply submitted independently of the Reston conference. Thus, this book is not a proceedings of that conference, nor was it ever intended to be. The chapters presented here range from theory of bonding and structure, to structurally oriented measurements of various kinds, e.g., ESR, Raman, to more applied chapters. Our goal was to produce a monograph that enhances understanding of the structures of NC solids.
When this innovative textbook first appeared in 1984 it rapidly became a great success throughout the world and has already been translated into several European and Asian languages. Now the authors have completely revised and updated the text, including more than 2000 new literature references to work published since the first edition. No page has been left unaltered but the novel features which proved so attractive have been retained. The book presents a balanced, coherent and comprehensive account of the chemistry of the elements for both undergraduate and postgraduate students. This crucial central area of chemistry is full of ingenious experiments, intriguing compounds and exciting new discoveries. The authors specifically avoid the term `inorganic chemistry' since this evokes an outmoded view of chemistry which is no longer appropriate in the final decade of the 20th century. Accordingly, the book covers not only the 'inorganic' chemistry of the elements, but also analytical, theoretical, industrial, organometallic, bio-inorganic and other cognate areas of chemistry. The authors have broken with recent tradition in the teaching of their subject and adopted a new and highly successful approach based on descriptive chemistry. The chemistry of the elements is still discussed within the context of an underlying theoretical framework, giving cohesion and structure to the text, but at all times the chemical facts are emphasized. Students are invited to enter the exciting world of chemical phenomena with a sound knowledge and understanding of the subject, to approach experimentation with an open mind, and to assess observations reliably. This is a book that students will not only value during their formal education, but will keep and refer to throughout their careers as chemists. - Completely revised and updated - Unique approach to the subject - More comprehensive than competing titles
Presenting the first book to focus on the importance of silicon for plant health and soil productivity and on our current understanding of this element as it relates to agriculture.Long considered by plant physiologists as a non-essential element, or plant nutrient, silicon was the center of attention at the first international conference on Silicon in Agriculture, held in Florida in 1999.Ninety scientists, growers, and producers of silicon fertilizer from 19 countries pondered a paradox in plant biology and crop science. They considered the element Si, second only to oxygen in quantity in soils, and absorbed by many plants in amounts roughly equivalent to those of such nutrients as sulfur or magnesium. Some species, including such staples as rice, may contain this element in amounts as great as or even greater than any other inorganic constituent. Compilations of the mineral composition of plants, however, and much of the plant physiological literature largely ignore this element. The participants in Silicon in Agriculture explored that extraordinary discrepancy between the silicon content of plants and that of the plant research enterprise.The participants, all of whom are active in agricultural science, with an emphasis on crop production, presented, and were presented with, a wealth of evidence that silicon plays a multitude of functions in the real world of plant life. Many soils in the humid tropics are low in plant available silicon, and the same condition holds in warm to hot humid areas elsewhere. Field experience, and experimentation even with nutrient solutions, reveals a multitude of functions of silicon in plant life. Resistance to disease is one, toleration of toxic metals such as aluminum, another. Silicon applications often minimize lodging of cereals (leaning over or even becoming prostrate), and often cause leaves to assume orientations more favorable for light interception. For some crops, rice and sugarcane in particular, spectacular yield responses to silicon application have been obtained. More recently, other crop species including orchids, daisies and yucca were reported to respond to silicon accumulation and plant growth/disease control. The culture solutions used for the hydroponic production of high-priced crops such as cucumbers and roses in many areas (The Netherlands for example) routinely included silicon, mainly for disease control. The biochemistry of silicon in plant cell walls, where most of it is located, is coming increasingly under scrutiny; the element may act as a crosslinking element between carbohydrate polymers.There is an increased conviction among scientists that the time is at hand to stop treating silicon as a plant biological nonentity. The element exists, and it matters.