With 1 hetero atom other

Boranes with Hetero Atoms Other Than Carbon... 

The structure of this chapter is as follows. As it concerns [AIJ-MTS, first discussed are the cation-exchanged samples, potentially exhibiting basic behavior, then the H-forms, the acidic properties of which are, as a whole, the main subject, finally the development of acidity upon partial exchange of cations with protons. The last section is devoted to a brief description of MTS with hetero atoms other than Al. 

The first chapter concerns the chemistry of the oxidation catalysts, some 250 of these, arranged in decreasing order of the metal oxidation state (VIII) to (0). Preparations, structural and spectroscopic characteristics are briefly described, followed by a summary of their catalytic oxidation properties for organic substrates, with a brief appendix on practical matters with four important oxidants. The subsequent four chapters concentrate on oxidations of specific organic groups, first for alcohols, then alkenes, arenes, alkynes, alkanes, amines and other substrates with hetero atoms. Frequent cross-references between the five chapters are provided. 

Other analytical expressions for the potential have been proposed [27,46]. In particular, for taking into account molecules with hetero atoms and permanent dipoles that cannot be handled well with formula (1), the proposed potential is ... 

H-pyrrolo[2,l-a] isoindoles quinolines quinolizines quinuclidines with 1 hetero atom other than O or N dibenzostannols dinaphthothiophenes phospholines phosphorins stibiafluorenes thieno[4, 3, 2"-4,5,6]steroids Ihietanes thiochromans thiophenes thiopyrylium salts thioxanthylium salts with 2 0-atoms benzodioxanes benzofuro[2,3-b]benzofurans chromeno [3,4-bJ chromenes coumarinocoumarones dibenzo-p-dioxins... 

In this section, selected results for other polymers will be presented. It will be demonstrated that our method is applicable to a wide range of systems belonging to different structural classes, including the simplest polymer poly (ethylene) (PE), a bisubstituted polyolefine (poly (isobutylene), PIB), unsaturated systems (poly(butadiene), PBD and poly(isoprene), PIP), polymers with hetero atoms (poly(vinyl chloride), PVC), and extended sidegroups (poly(methyl methacrylate), PMMA). 

Surprisingly, the highest catalytic activity is observed in TFE. One mi t envisage this to be a result of the poor interaction between TFE and the copper(II) cation, so that the cation will retain most of its Lewis-acidity. In the other solvents the interaction between their electron-rich hetero atoms and the cation is likely to be stronger, thus diminishing the efficiency of the Lewis-acid catalysis. The observation that Cu(N03)2 is only poorly soluble in TFE and much better in the other solvents used, is in line with this reasoning. 

This chapter will deal exclusively with three-membered rings containing the hetero atoms O, S and N, and fused to the steroid skeleton. Because of the conformational requirements in steroids, not all of the usual methods of synthesis of three-membered rings are applicable to the fused ring system. For the synthesis of steroids to which an aziridine, oxirane or thiirane is attached either in the side chain or at a ring position but not directly fused to the nucleus, the methods discussed in this chapter, as well as others, are applicable. 

It should be expected that the orientation and rate of electrophilic substitution in the isoxazole nucleus would be affected by both hetero atoms. Because of the electron-accepting effect of the nitrogen atom, electrophilic substitution of the isoxazole nucleus should proceed less readily than in the case of benzene and should occur essentially at the position jS to the nitrogen atom, just as in pyridine and other azoles. Simultaneously the electron-donating oxygen atom should facilitate such reactions in isoxazole as compared with the substitution in pyridine. These predictions are confirmed by the available experimental evidence. 

In the following sections, systems with various numbers of electrons are discussed. When we look for aromaticity we look for (1) the presence of a diamagnetic ring current (2) equal or approximately equal bond distances, except when the symmetry of the system is disturbed by a hetero atom or in some other way (3) planarity (4) chemical stability (5) the ability to undergo aromatic substitution. 

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