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Organic reactions carbanions

Many in ortant organic reactions involve nucleophilic carbon species (carbanions). The properties of carbanions will be discussed in detail in Chapter 7 and in Part B,... [Pg.228]

Addition and substitution reactions of nitrile-stabilized carbanions S. Arseniyadis, K. S. Kyler and D. S. Watt, Organic Reactions 31,1 (1984). Note. Includes ArC (OTMS)CN, and HetAr (OTMS)CN. [Pg.164]

Although addition of HCN could be looked upon as a carbanion reaction, it is commonly regarded as involving a simple anion. It is of unusual interest in that it was almost certainly the first organic reaction to have its mechanistic pathway established (Lapworth 1903). HCN is not itself a powerful enough nucleophile to attack C=0, and the reaction requires base-catalysis in order to convert HCN into the more nucleophilic CN the reaction then obeys the rate law ... [Pg.212]

Biocatalytk decarboxylation is a imique reaction, in the sense that it can be considered to be a protonation reaction to a carbanion equivalent intermediate in aqueous medimn. Thus, if optically active compoimds can be prepared via this type of reaction, it would be a very characteristic biotransformation, as compared to ordinary organic reactions. An enzyme isolated from a specific strain of Alcaligenes bronchisepticus catalyzes the asymmetric decarboxylation of a-aryl-a-methyhnalonic acid to give optically active a-arylpropionic acids. The effect of additives revealed that this enzyme requires no biotin, no co-enzyme A, and no ATP, as ordinary decarboxylases and transcarboxylases do. Studies on inhibitors of this enzyme and spectroscopic analysis made it clear that the Cys residue plays an essential role in the present reaction. The imique reaction mechanism based on these results and kinetic data in its support are presented. [Pg.1]

As noted in Section 4.2.1, the gas phase has proven to be a useful medium for probing the physical properties of carbanions, specifically, their basicity. In addition, the gas phase allows chemists to study organic reaction mechanisms in the absence of solvation and ion-pairing effects. This environment provides valuable data on the intrinsic, or baseline, reactivity of these systems and gives useful clues as to the roles that solvent and counterions play in the mechanisms. Although a variety of carbanion reactions have been explored in the gas phase, two will be considered here (1) Sn2 substitutions and (2) nucleophilic acyl substitutions. Both of these reactions highlight some of the characteristic features of gas-phase carbanion chemistry. [Pg.108]

Since the sensitivity towards water in many organic reactions lies in the order carbanion > carbonium ion > free radical, it appears likely that as water is progressively removed from a-methylstyrene—and, perhaps, other vinyl monomers—the free radical propagation is augmented or supplanted by a carbonium ion mechanism, which, in turn, is further enhanced at low water content, by a carbanion mechanism. Under the latter conditions, one would expect a termination mechanism which is bimolecular with regard to the total concentration of propagating species and hence a square-root dependence of the polymerization rate on the dose rate. This is the order dependence observed in a-methylstyrene at the highest polymerization rates and lowest water content. [Pg.191]

Examples for frequently encountered intermediates in organic reactions are carbocations (carbenium ions, carbonium ions), carbanions, C-centered radicals, carbenes, O-centered radicals (hydroxyl, alkoxyl, peroxyl, superoxide anion radical etc.), nitrenes, N-centered radicals (aminium, iminium), arynes, to name but a few. Generally, with the exception of so-called persistent radicals which are stabilized by special steric or resonance effects, most radicals belong to the class of reactive intermediates. [Pg.155]

This resonance-stabilized carbanion must be sp2 hybridized and planar for effective delocalization of the negative charge onto oxygen (Section 2-6). Resonance-stabilized carbanions are the most common type of carbanions we will encounter in organic reactions. [Pg.166]

In organic reactions there is abundant evidence for transient carbonium ions (R3C+), carbanions (R3C ), and carbenes ( CR2). Some stable carbonium ions like Ph3C+ and carbanions like C(CN)3 can be isolated as well as radicals like Ph3C In most of these cases the charge on the electron must be delocalized over the entire system for stability. Transition metal complexes with carbene or carbyne ligands, L M=CR2 and L M=CR, are discussed in Chapters 16 and 21. [Pg.208]

The book is divided into three parts. Part I deals with typical complex organic reactions such as (i) reactions involving carbocations and carbanions, (i/) Pericyclic and electrocyclic reactions and (ii/) Sigmatropic and Chelotropic reactions. This part also includes material useful for characterization of products from structural point of view such as Geometrical isomerism, Stereochemistry and Conformation. Part II is concerned with spectroscopic methods of structure determination such as U.V.,... [Pg.325]

The reactions of toluene illustrate a very important peculiarity of many organic reactions they proceed with the involvement of high-energy intermediates. The structure and reactivity of these species are actually the main factors that determine both the viability of the reactions and the pathways they would take. In the above examples, species like Br , Br", CHsCO", 7-complex 13, radical-anion 14, and carbanion 15 participated as intermediates. These intermediates, however, should never be confused with transition states even though they may often be similar in energy and structure. The differences can be best illustrated by means of the energy profile diagram presented in Fig. 4. [Pg.53]

Manchester) in 1904, showed for the first time how kinetics could be used to reveal the mechanism of an organic reaction. The carbanion mechanism has since been confirmed not only by the iodination work, but also by studies of stereochemistry and isotopic exchange. [Pg.707]


See other pages where Organic reactions carbanions is mentioned: [Pg.45]    [Pg.325]    [Pg.437]    [Pg.507]    [Pg.45]    [Pg.137]    [Pg.371]    [Pg.237]    [Pg.185]    [Pg.240]    [Pg.55]    [Pg.277]    [Pg.293]    [Pg.164]    [Pg.821]    [Pg.65]    [Pg.153]    [Pg.309]    [Pg.821]    [Pg.166]    [Pg.418]    [Pg.852]    [Pg.5984]    [Pg.3]    [Pg.39]    [Pg.2]    [Pg.38]    [Pg.115]    [Pg.373]    [Pg.655]    [Pg.229]   
See also in sourсe #XX -- [ Pg.111 , Pg.112 ]

See also in sourсe #XX -- [ Pg.104 , Pg.105 ]




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Carbanion reactions

Carbanions reactions

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