Anions carbon

Carbides, which are binary compounds containing anionic carbon, occur as covalent and as salt-like compounds. The salt-like carbides are water-reactive and, upon hydrolysis, yield flammable hydrocarbons. Typical hydrolysis reactions include ... 

The ways in which inhibitive anions affect the corrosion of zinc are mainly similar to those described above for iron. In inhibition by chromate, localised uptake of chromium has been shown to occur at low chromate concentrations and in the presence of chloride ions Thus under conditions unfavourable for inhibition, pore plugging occurs on zinc. Inhibitive anions also promote the passivation of zinc, e.g. passivation is much easier in solutions of the inhibitive anion, borate , than in solutions of the non-inhibitive anions, carbonate and bicarbonate , A critical... 

Eisch, Behrooz and Galle196 give compelling evidence for the intervention of radical species in the desulphonylation of certain acetylenic or aryl sulphones with metal alkyls having a lower oxidation potential at the anionic carbon. The primary evidence presented by these workers is that the reaction of 5-hexenylmagnesium chloride outlined in equation (85) gives a mixture of desulphonylation products, in accord with the known behaviour of the 5-hexenyl radical, in which the cyclopentylmethyl radical is also formed. 

In the presence of mineral phases containing anions that would form sparingly soluble compounds (e.g. POt - and F for the lower oxidation states) an enhanced plutonium uptake due to chemisorption can be expected (57). For plutonium in the higher oxidation states the formation of anionic carbonate complexes would drastically reduce the sorption on e.g oxide and silicate surfaces. 

Solids containing oxidized anions (carbonates, sulfates, hydroxides, and oxides) are the dominant forms of Cu in airborne particulate matter. In the few studies that have addressed the reactions of these particles in atmospheric washout, about 50% of the copper has been found to be soluble. Since the solubility is strongly dependent on pH, acid precipitation and acidification of receiving waters may have a significant effect on the form and fate of airborne copper. 

The reaction presumably involves protonation of the oxygen, followed by attack of the carbonium ion (C —OH) on the coordinated, anionic carbon atom. (The exo form undergoes cyanide insertion in acid see Section VI,D). 

In contrast to the early theoretical work of Rank and coworkers , C-NMR investigations had revealed that the metallated carbon atom in the a-sulphinyl carbanion is nearly planar . A four-centre chelate structure 315 has been proposed for a-lithiosulphoxides, and it is believed to be responsible for the planar configuration of the anionic carbon atom and for the greater stability of o(-sulphinyl carbanions in comparison with a-sulphenyl carbanions This chelation favours one of the two diastereoisomeric carbanions and for this reason a-sulphinyl carbanions react with electrophiles in a highly stereoselective manner (see below). 

Alkylation of dianions occurs at the more basic carbon. This technique permits alkylation of 1,3-dicarbonyl compounds to be carried out cleanly at the less acidic position. Since, as discussed earlier, alkylation of the monoanion occurs at the carbon between the two carbonyl groups, the site of monoalkylation can be controlled by choice of the amount and nature of the base. A few examples of the formation and alkylation of dianions are collected in Scheme 1.7. In each case, alkylation occurs at the less stabilized anionic carbon. In Entry 3, the a-formyl substituent, which is removed after the alkylation, serves to direct the alkylation to the methyl-substituted carbon. Entry 6 is a step in the synthesis of artemisinin, an antimalarial component of a Chinese herbal medicine. The sulfoxide serves as an anion-stabilizing group and the dianion is alkylated at the less acidic a-position. Note that this reaction is also stereoselective for the trans isomer. The phenylsulfinyl group is removed reductively by aluminum. (See Section 5.6.2 for a discussion of this reaction.)... 

Participation by the enolate anion could, in principle, act via either the anionic carbon or oxygen. The former, however, is known to be considerably the more nucleophilic centre. The latter would give rise to a lactone, which would be rapidly hydrolysed under the usual conditions of excess base to give the identical final product. There is no evidence for the occurrence of such a process. 

Both stabilized and unstabilized lithium reagents have been used as a source of anionic carbon for displacement of halogen from phosphorus in the generation of carbon-phosphorus bonds. 

Other eluent systems in suppressed ion chromatography are typically chosen based on specific separation requirements. For routine analysis of monovalent and divalent anions, carbonate-based eluents represent a reasonable alternative to hydroxide-based eluent systems. Carbonate eluents are simple to prepare and can be useful in cases where anion analysis is only occasionally performed. It must be kept in mind, however, that carbonate lowers the detection sensitivity for anionic species and introduces significant nonlinearity into the analysis. ... 

Substitution of one dimethylamino group by alkyl, aryl, or alkynyl groups in complexes [M =C=C=C(NMe2)2 (CO)5] (M = Cr, W 51) has also been described [9]. The process occurs through an initial addition of the anionic carbon nucleophile to the Cy atom of 51 and subsequent abstraction of one dimethylamido... 

Nucleophilic substitution reactions employing carbon as a nucleophile are important in synthetic chemistry in that they create a new C-C bond. A carbon nucleophile, of course, must be in the form of anionic carbon, or its equivalent. One of the simplest sources of anionic carbon is the cyanide anion. HCN is a weak acid (pATa 9.1) and forms a series of stable... 

Electrophiles that have been used for the second alkylation of this tandem Michael addition -alkylation sequence are limited to primary iodoalkanes, (bromomethyl)benzenes and 3-bromo-propenes. Tables 9 and 10 provide details of the alkylations of enolate species prepared by 1,4-additions of -a,/j-unsaturated iron-acyl complexes by anionic carbon nucleophiles and anionic nitrogen nucleophiles, respectively. 

Internal nucleophilic cyclization leading to alkoxycyclopropanes is the most typical reaction of reactive metal homoenolates [I, 2]. The nature of stable homoenolates, however, is such that the anionic carbon C-3 forms a covalent bond with the metal atom and does not show high nucleophilic reactivity. 

In phosphonium ylides, as we shall see in Section II. A, the phosphorus atom is tetracoordi-nate and the unique (anionic) carbon is tricoordinate. For exactly the same reasons as in the oxides2, all previous discussions3-14 of the P—C bond have been in terms of a resonance hybrid between a dipolar form 1A and a double bond form IB ... 

Five- (and six-) membered phosphorus ylides with an exocyclic anionic carbon atom as in (173) add MeOH or HF (NFUF) giving phosphoranes (174) and (175), respectively (Scheme 27) (79MI11704). A second example, addition of C1F with S02C1F (176- 177), was recently found by the author (83UP11701). 

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