Carbon oxide anions

The three carbon oxide anions, C303 [1603], 404 [1604], andCsOs [1604], take the planar ring structures shown in Fig. 2.60. Because of aromaticity of these rings, their IR spectra exhibit the C=0 stretching vibrations below 1600 cm which are much lower than those of normal ketones ( 1700 cm ). 

The benzylidene derivative above is used, if both hydroxyl groups on C-2 and C-3 are needed in synthesis. This r/vzns-2,3-diol can be converted to the sterically more hindered a-cpoxide by tosylation of both hydroxy groups and subsequent treatment with base (N.R. Williams, 1970 J.G. Buchanan, 1976). An oxide anion is formed and displaces the sulfonyloxy group by a rearside attack. The oxirane may then be re-opened with nucleophiles, e.g. methyl lithium, and the less hindered carbon atom will react selectively. In the following sequence starting with an a-glucoside only the 2-methyl-2-deoxyaltrose is obtained (S. Hanessian, 1977). 

Weak to moderate chemiluminescence has been reported from a large number of other Hquid-phase oxidation reactions (1,128,136). The Hst includes reactions of carbenes with oxygen (137), phenanthrene quinone with oxygen in alkaline ethanol (138), coumarin derivatives with hydrogen peroxide in acetic acid (139), nitriles with alkaline hydrogen peroxide (140), and reactions that produce electron-accepting radicals such as HO in the presence of carbonate ions (141). In the latter, exemplified by the reaction of h on(II) with H2O2 and KHCO, the carbonate radical anion is probably a key intermediate and may account for many observations of weak chemiluminescence in oxidation reactions. 

The saline carbides are formed most commonly from the metals of Groups 1 and 2, aluminum, and a few other metals. The s-block metals form saline carbides when their oxides are heated with carbon. The anions present in saline carbides are either C>2 or C4. All the C4 carbides, which are called methides, produce methane and the corresponding hydroxide in water ... 

The retro Diels-Alder reaction is strongly accelerated when an oxide anion substituent is incorporated at positions 1 and 2 of the six-membered ring which has to be cycloreversed, namely at one terminus carbon of the original diene or at one sp carbon of the dienophile [51] (Equation 1.22). 

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. 

FeC03 This ionic compound contains the carbonate polyatomic anion, C O3. The -2 charge on carbonate requires that iron have +2 oxidation number (Guideline 2). In the carbonate anion, each oxygen atom is -2, for a total of-6. The oxidation numbers must add up to the net charge on the anion (-2), so the carbon atom must have an oxidation number of +4. 

XOR is a cytoplasmic enzyme and a ready source of electrons for transfer to molecular oxygen to form reactive oxygen species such as superoxide and peroxide. It is therefore thought to be involved in free radical-generated tissue injury and has been implicated in the pathogenesis of ischemia-reperfusion damage. Moreover, it has recently been implicated in the production of peroxynitrite (89), and carbonate radical anion (92), both potent biological oxidants. Its exact role in lipid peroxidation, inflammation, and infection needs... 

The cation pool method is based on the irreversible oxidative generation of organic cations. In the first step, the cation precursor is oxidized via an electrochemical method. An organic cation thus generated is accumulated in the solution in the absence of a nucleophile that we want to introduce onto the cationic carbon. Counter anions which are normally considered to be very weak nucleophiles are used to avoid the nucleophilic attack on the cationic center. In order to avoid thermal decomposition of the cation, electrolysis should be carried out at low temperatures such as -78 °C. After electrolysis is complete, the nucleophile is then added to obtain the desired product. The use of a carbon nucleophile results the direct carbon-carbon bond formation. 

In the pyridine A-oxide anion-radical, the greatest spin density belongs to the carbon atom in the position 2 (Chaha 1986). In accordance with this, a reaction between the pyridine A-oxide anion-radical and the benzophenone metal ketyl yielded preferentially 2-diarylcarbinole derivatives (Kurbatova et al. 1980, Turaeva et al. 1993 Scheme 3.10). 

In this type of spin traps, 5,5-dimethyl-l-pyrroline-Af-oxide (DMPO) deserves particular mention. DMPO is widely employed as a spin trap in the detection of transient radicals or ion-radicals in chemical and biological systems (see, e.g., Siraki et al. 2007). Characteristic ESR spectra arising from the formation of spin adducts are used for identification of specific spin species. In common opinion, such identification is unambiguous. However, in reactions with superoxide ion (Villamena et al. 2004, 2007b), carbon dioxide anion-radical (Villamena et al. 2006), or carbonate anion-radical (Villamena et al. 2007a), this spin trap gives rise to two adducts. Let us consider the case of carbonate anion-radical. The first trapped product arises from direct addition of carbonate anion-radical, second adduct arises from partial decarboxylation of the first one. Scheme 4.25 illustrates such reactions based on the example of carbonate anion-radical. 

Guanine is the most easily oxidizable natural nucleic acid base [8] and many oxidants can selectively oxidize guanine in DNA [95]. Here, we focus on the site-selective oxidation of guanine by the carbonate radical anion, COs , one of the important emerging free radicals in biological systems [96]. The mechanism of COs generation in vivo can involve one-electron oxidation of HCOs at the active site of copper-zinc superoxide dismutase [97, 98], and homolysis of the nitrosoperoxycarbonate anion (0N00C02 ) formed by the reaction of peroxynitrite with carbon dioxide [99-102]. 

The above authors rationalized formation of the more hindered i omer by assuming the equilibrium to be displaced in its favor by virtue of the lower solubility of this isomn relative to the other. House and Ho,885 on the other hand, showed by deuteration experiments and nuclear magnetic resonance spectroscopy that the epimeriza-tion observed by Washerman and oo-workera1Wfi IH0 proceeds by way of an unueual oxide anion in which negative charge resides on carbon as ehovra in Eq. (SS). 

C. Crean et al., Oxidation of guanine and 8-oxo-7, 8-dihydroguanine by carbonate radical anions Insight from oxygen-18 labeling experiments. Angew. Chem. Int. Ed. 44, 5057-5060 (2005)... 

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