Allyl anions defined

Extensive theoretical studies have been carried out to probe the nature of the allyl anion. These studies supplement and extend the experimental results. Allyl anion is of special interest because it is the simplest 7r-delocalized carbanion with 4 electrons and 3 Pjr-centers. Much recent theoretical discussion has concerned the role of resonance in the stabilization of such conjugated systems, a stabilization defined as the enthalpy difference between the localized double-bonded system and its conjugated state. The stabilization of allyl anion has generally been attributed to the delocalization of charge associated... 

Figure 4.2 Hiickel MOs for the allyl system. One pc orbital per atom defines the basis set. Combinations of these 3 AOs create the 3 MOs shown. The electron occupation illustrated corresponds to the allyl cation. One additional electron in

An allyl anion has two more electrons, but the complication with anions is that they are often ill defined, usually being organometallic species with a... 

More recently, Majetich et al. have proposed pentacoordinate allylsilicate intermediates formed from fluoride ion addition to silicon as an ambient nucleophilic species. However, nothing had been known so far about pentacoordinate allylsilicates, before we have initiated the present study, whereas a number of pentacoordinate organosilicates have been well characterized. It is an interesting problem whether the fluoride-catalyzed reactions actually involve free allyl anions or not. The author will discuss this problem in the next section somewhat in detail. In this section the author will describe preparation of well-defined pentacoordinate allylsilanes and their reactions which have been published recently. ... 

PS macromonomers have been efficiently applied to the synthesis of well-defined polymer hybrids with controlled length of grafts. They are, in general, prepared via living anionic polymerization of styrene monomers and their treatment with vinyl compounds, such as -allyl, -undecenyl, and styryl compounds. 

Anions (53) undergo only a-attack with TMS-Cl or BusSnCl to give (54 equation 50). The stereochemistry of compounds (54) has not been defined, but upon reaction with water they give only the (Z)-allyl-silicon or -tin derivatives (55). ... 

Ionic grafting usually leads to well defined copolymers due to the limited (if any) termination reactions. Anionic sites can be created by metallation of the backbone. This can be accomplished by complexation of several types of C-H bonds (allylic, benzylic, aromatic) with organometallic compounds such as sec-BuLi. Usually chelating compounds, for example N,N,N/>N/-tetra methyl ethylene diamine (TMEDA), act as solvating bases facilitating the reaction. By this method PB-g-PS [36-38] and Pl-g-PS [39] graft copolymers have been prepared. 

The end-functionalized PEO block was prepared via an etherification reaction between an HO-terminated poly(ethylene oxide) of a defined block length and allyl bromide. The SiH-functionalized polysiloxane was prepared by anionic ring-opening polymerization (ROP) of hexamethylcyclotrisiloxane (D3) and quenching of the chain end with chlorodimethylsilane (Scheme 1) [3]. 

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