Spectroscopic properties structural aspects

III. Spectroscopic Properties, Structural Aspects, and Analytical Detection. 99... 

This chapter reviews the body of literature (to August 2000) that deals specifically with kinetic studies of the reactions of silenes and disilenes and the mechanistic information that has been derived from them. The spectroscopic properties, structures, methods of synthesis and qualitative aspects of the reactivity of silenes and disilenes have been covered comprehensively in the preceding two volumes in this series and elsewhere, and so will not be treated extensively here. 

In CHEC-I <84CHEC-l(3B)l>, theoretical methods, particularly the calculation of bond lengths, bond angles, and electron densities were discussed alongside consideration of structure, and physical and spectroscopic properties. Theoretical aspects since 1984 are summarized below. 

In the following sections structure, thermodynamic aspects, theoretical calculations, spectroscopic properties, reactions, syntheses, and more briefly, utilization of the representatives of these ring systems are discussed. 

We have already pointed out in the Introduction (see above) that the first review article on radialenes is only a few years old1. In this first summary we have enclosed a comprehensive survey and discussion of the structural and spectroscopic properties of the radialenes. Since progress in this latter area has not been very rapid in the last few years, we do not address here again these aspects of the radialenes. Furthermore, nothing new can be added to the statement that all radialenes are nonaromatic and that they have localized endocyclic single bonds and exocyclic double bonds1 (for recent discussions of ji-ji interaction in [5]- and [3]radialene, see elsewhere903 109). 

In 1998, Hasanayn and Streitwieser reported the kinetics and isotope effects of the Aldol-Tishchenko reaction . They studied the reaction between lithium enolates of isobu-tyrophenone and two molecule of beuzaldehyde, which results iu the formation of a 1,3-diol monoester after protonation (Figure 28). They analyzed several aspects of this mechanism experimentally. Ab initio molecular orbital calculatious ou models are used to study the equilibrium and transition state structures. The spectroscopic properties of the lithium enolate of p-(phenylsulfonyl) isobutyrophenone (LiSIBP) have allowed kinetic study of the reaction. The computed equilibrium and transition state structures for the compounds in the sequence of reactions in Figure 28 are given along with the computed reaction barriers and energy in Figure 29 and Table 6. 

It is therefore the right time to give a first comprehensive overview of fullerene chemistry, which is the aim of this book. This summary addresses chemists, material scientists and a broad readership in industry and the scientific community. The number of publications in this field meanwhile gains such dimensions that for nonspecialists it is very difficult to obtain a facile access to the topics of interest. In this book, which contains the complete important literature, the reader will find all aspects of fullerene chemistry as well as the properties of fullerene derivatives. After a short description of the discovery of the fullerenes all methods of the production and isolation of the parent fullerenes and endohedrals are discussed in detail (Chapter 1). In this first chapter the mechanism of the fullerene formation, the physical properties, for example the molecular structure, the thermodynamic, electronic and spectroscopic properties as well as solubilities are also summarized. This knowledge is necessary to understand the chemical behavior of the fullerenes. 

This chapter is divided into four major sections. The first (Section 2.1) will deal with the structure of both alkoxy and silyl nitronates. Specifically, this section will include physical, structural, and spectroscopic properties of nitronates. The next section (Section 2.2) describes the mechanistic aspects of the dipolar cycloaddition including both experimental and theoretical investigations. Also discussed in this section are the regio- and stereochemical features of the process. Finally, the remaining sections will cover the preparation, reaction, and subsequent functionalization of silyl nitronates (Section 2.3) and alkyl nitronates (Section 2.4), respectively. This will include discussion of facial selectivity in the case of chiral nitronates and the application of this process to combinatorial and natural product synthesis. 

In the following sections structure, thermodynamic aspects, theoretical calculations, spectroscopic properties, reactions, syntheses, and, more briefly, the uses of these tricyclic ring systems are discussed. Within the individual subsections of reactivity, synthesis, and applications, the pyrim-ido[l,2-6]isoquinolines, pyrido[2,l-6]quinazolines, pyrimido[l,2-a]quino-lines, pyrido[l,2-a]quinazolines, and pyrimido[2,l-a]isoquinolines are considered. 

This chapter avoids the extensive tabulations of physical and spectroscopic properties that characterized its predecessor. Instead, emphasis is placed on the structural and electronic aspects of the coordination chemistry of the 1,1-dithio ligands. 

In 1981, West et al. synthesized the first stable disilene 1 via the dimerization of the corresponding silylene generated by the photolysis of a trisilane and characterized the structure by conventional spectroscopies [Eq. (2)].5 Availability of 1 and other stable disilenes has stimulated theoretical and experimental studies of various aspects of disilenes such as their bonding and structure, spectroscopic properties, reactivities, applications to the synthesis of novel types of organosilicon compounds, etc. 

The structures of type II copper sites have not as yet generated as much interest, but the hetero-dinuclear structures of type IIC copper sites and the unusual protein donor ligands found in type IIB copper sites are noteworthy. The synthetic model approach to gain insight into the structures and functions of these types of copper sites will be also described. The diverse functions of a variety of proteins containing type IIA copper sites inspired many chemists to mimic the functions with synthetic copper complexes, even though the spectroscopic properties of the complexes are not unusual. Results of these studies will be reviewed and different aspects of the reactions relating to enzymatic catalysis will be discussed. 

All of the special techniques used for metalloenzymes are most useful when analogous small molecules have been prepared by inorganic synthesis and characterized by X-ray crystallography. The preparation of these model complexes allows a given physical property to be associated with a particular coordination structure or oxidation state. Synthesis of model complexes with structural, functional, or spectroscopic properties relevant to a particular metalloenzyme is a vital aspect of bioinorganic chemistry (13) and is described in numerous chapters in this volume. 

Mixed donor ligands present a challenge to the coordination chemist as a result of structural aspects discussed above. Further, the presence of donors of distinctly different character, such as an N-donor and an S-donor, influence the way they select metal ions, and the stabihty, spectroscopic, and redox properties of their complexes. 

Another controversial aspect of the bishydrazone structure concerns the hydrazone residues. The bishydrazone was proposed to have the structure 46, which mutarotates in solution to 47 (47). More recently, on the basis of a comparative study of the spectroscopic properties of the bis(phenylhydrazone) with some related compounds, the bishydrazone was assigned the structure 2,3-dideoxy-3-phenylazo-2-phenylhydrazino-L-threo-hex-2-enone-l,4-lactone (48) (48). However, this latter structure was inconsistent with its NMR spectra (49). 

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