Structures and bond nature

A common feature of all group 14 heavy element triply-bonded compounds is their trans-bent structure, 657 26 258 262 340-356, in contrast to the linear Doch structure (66) 

Calculations for MeMMMe, M = Ge, Sn led to the conclusion that the M—M bond in these molecules is a double bond rather than a triple bond. Thus, the Pauling bond 

TABLE 34. Geometrical parameters and linearization energies AE(65-66) of trans-bent HMsM H (65)a 

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In the present study, we used a neutral C-M6-C12-C6 cluster model (abbreviated as MODEL I) for TiC and UC compounds in order to compare their electronic structures and bond natures. However, this model does not represent the bulk state of TiC and UC strictly, because outermost atoms of the cluster are not located in their bulk potential. In order to calculate solid-state electronic structures more accurately than MODEL I, we developed a chemically complete cluster model (abbreviated as MODEL II) by introducing periodic potentials to MODEL I and examined this modified model for TiC. We compared the valence electronic sti ucture of TiC between the two cluster models and demonstrate the advantages of MODEL II in this work. 

After the discovery of quantum mechanics in 1925 it became evident that the quantum mechanical equations constitute a reliable basis for the theory of molecular structure. It also soon became evident that these equations, such as the Schrodinger wave equation, cannot be solved rigorously for any but the simplest molecules. The development of the theory of molecular structure and the nature of the chemical bond during the past twenty-five years has been in considerable part empirical — based upon the facts of chemistry — but with the interpretation of these facts greatly influenced by quantum mechanical principles and concepts. 

From the viewpoint of structural chemistry, structure and bonding lie at the heart of rational syntheses that have already contributed to many significant scientific advances in inorganic chemistry and material chemistry, and especially to the discovery of some functional materials. Naturally the first step to novel functional material is synthesis , and in many cases exploratory synthesis seems to be the only workable route to new compound. However, rational synthesis will surely make property-oriented exploration more fruitful and pleasing. 

Pauling, L. (1960). The Nature of the Chemical Bond, 3rd ed. Cornell University Press, Ithaca, NY. A classic book that presents a good description of crystal structures and bonding in solids. 

Raman spectroscopy is primarily useful as a diagnostic, inasmuch as the vibrational Raman spectrum is directly related to molecular structure and bonding. The major development since 1965 in spontaneous, c.w. Raman spectroscopy has been the observation and exploitation by chemists of the resonance Raman effect. This advance, pioneered in chemical applications by Long and Loehr (15a) and by Spiro and Strekas (15b), overcomes the inherently feeble nature of normal (nonresonant) Raman scattering and allows observation of Raman spectra of dilute chemical systems. Because the observation of the resonance effect requires selection of a laser wavelength at or near an electronic transition of the sample, developments in resonance Raman spectroscopy have closely paralleled the increasing availability of widely tunable and line-selectable lasers. 

Simon, W., Morf, W. E., and Meier, P. Ch. Specificity for Alkali and Alkaline Earth Cations of Synthetic and Natural Organic Complexing Agents in Membranes. Vol. 16, pp. 113—160. Sinha, S. P. Structure and Bonding in Highly Coordinated Lanthanide Complexes. Vol. 25. pp. 67-147. 

These characteristics presumably would also be imparted to the apolar binding groups and nucleophilic catalytic moieties covalendy bonded to the polymer. A structure with such features has the potential of being an effective catalyst in a variety of reactions with a range of substrates of widely differing structure and chemical nature. 

Most of the general principles of molecular structure and the nature of the chemical bond were formulated long ago by chemists by indue-tion from the great body of chemical facts. During recent decades these principles have been made more precise and more useful through the application of the powerful experimental methods and theories of modem physics, and some new principles of structural chemistry have also been discovered. As a result structural chemistry has now become significant not only to the various branches of chemistry but also to biology and medicine. 

The amount of knowledge of molecular structure and the nature of the chemical bond is now very great. In this book I shall attempt to present only an introduction to the subject, with emphasis on the most important general principles. 

Bicyclo[2.1.0]pentene, 116, can be considered to be the prototype of a neutral homoantiaromatic molecule. The types of structural and bonding effects found for this molecule parallel in many respects those found for the bicyclo[3.1.0]hexenyl cation reported above. Further studies on both of these 4q systems will likely be rewarding in terms of fully understanding the nature of cyclopropyl homoconjugation and homoantiaromaticity. 

LIPSCOMB. WILLIAM N. l 1919—). An American chemist who won the Nobel prize fur chemistry in 1976 for his studies on ihe structure and bonding mechanisms of borancs. Much ol Hie research concerned structure and function of enzymes and natural products in organic and theoretical chemistry. He studied at (he Universities of Kentucky. California, and Minnesota. 

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