Chemical heteroatomic functionalized substitutents

The chemical and physical properties of polysilanes are strongly influenced by substituents attached to the polymer backbone. In this respect, heteroatom-substituted polysilanes should be very much intriguing on their properties. However, heteroatom-functional substituents such as amino and alkoxy groups on silicon cannot survive under the vigorous synthetic conditions of polysilanes by the conventional Wurtz-type condensation of dichlorosilanes. Therefore, it is difficult to prepare heteroatom-functional polysilanes. We have recently found that amino-substituted masked disilenes can be prepared and polymerized successfully to unprecedented amino-substituted polysilane of the completely alternative structure, poly[l,l,2-trimethyl-2-(dialkylamino)disilene]. 

Substitutive Nomenclature. The first step is to determine the kind of characteristic (functional) group for use as the principal group of the parent compound. A characteristic group is a recognized combination of atoms that confers characteristic chemical properties on the molecule in which it occurs. Carbon-to-carbon unsaturation and heteroatoms in rings are considered nonfunctional for nomenclature purposes. 

Current IUPAC and Chemical Abstracts nomenclature has been employed in this index with the former given preference. Substitutive nomenclature has been given preference over radicofunc-tional, additive, subtractive, conjunctive or replacement nomenclature, except where this becomes unwieldy. With many bicyclic and polycyclic compounds bearing heteroatoms, standard bicyclic or polycyclic oxa, aza, and thia replacement nomenclature has often been used. With certain functional groups, where the names are rather complex and probably not familiar to most organic chemists, such as ylides, those compounds have simply been named as sulfur, tellurium and arsonic ylides. Metal catbenes have been treated similarly. With more complex functionality and many heterocycles, the Beilstein Commander Crossfire nomenclature system has been used with certain modifications. 

While 3-methylenecephams themselves are completely devoid of antimicrobial activity, the exomethylene function is a distinctive feature of these compounds that many workers recognized could be a key intermediate in a chemical route to novel classes of cephalosporins with direct heteroatom substitution at C-3. Whereas 3-methylenecephams were first employed to produce deacetoxycephalosporins, exploration of their chemistry has led to the preparation of 3-chloro-3-cephems and 3-methoxyl-3-cephems that possess marked antimicrobial activity. These compounds represent a new and different generation of cephalosporin antibiotics. Two members of this class of p-lactams have achieved clinical importance. One bears the D-phenylglycyl side chain Lilly compound 99638, with the generic name cefaclor (Ceclor, Lilly). The other bears the D-cyclohexadienylglycyl side chain Ciba-Geigy Compound 9000. Both compounds are potent broad-spectrum p-lactam antibiotics with oral therapeutic efficacy. 

Fig. 3.5 Schematic representation of the chemical interactions in the cellulose/silica hybrids functionalized with HP A. In the ball and stick representation of the Keggin structure, the substituting heteroatom (vanadium) is shown in blue (Reprinted with permission from Ref [70], Copyright 2012, Royal Society of Chemistry)...

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