Dianion radicals

Another example from the same paper16 involves the cyanocarbon anion, 1,1,2,3,3-pentacyanopropene. One-electron reduction produces the expected dianion radical, the spectrum of which is shown in Figure 2.9. However, further reduction leads to a very different spectrum, which results from loss of CN from position 2, and attachment of a proton (presumably from the solvent A-,A -dimethy 1 lbrmamide) to produce the 1,1,3,3,-tetracyanopropene dianion radical the spectrum of which is also shown in Figure 2.9. 

This reaction sequence is completed by protolytic reactions of the dianionic radicals. 

There are a large number of spectroscopic reports involving Erythrosin, particularly from Russian laboratories. The near-IR absorption spectra of both Eosin and Erythrosin triplets and their dianion radical cations have been reported [236], the pK s of both species measured [237], and the influence on radiative and radiationless transitions by external heavy atoms such as iodide reported [238]. The nonradiative decay of Erythrosin in water at room temperature has also been studied by photoacoustic spectroscopy [239],... 

Dianion radicals formed in path (c) of Scheme 1-29 are inherently unstable species because they bear a double negative charge as well as an odd electron. The nitro group can exert an unusually stabilizing effect since it can fasten both a negative charge and an added electron. As seen in Table 1-4, the anion radicals are less acidic than their parent com-... 

Conditions under which anion-radicals are commonly made, e.g., reaction with an alkali metal in an ethereal solvent, are strongly basic. Azoles without a nitrogen substituent in general, therefore, lose the proton from the heteroatom before the electron is added and, when the latter is added, the product is a dianion radical. Conversely, on oxidation of an azole to give a cation-radical, if the heteroatom is unsubstituted, the proton may be lost, yielding a neutral azolyl radical. Thus, from azoles various radicals may be formed dianion, anion, neutral, or cation-radicals according to the nature of the substituent at N. 

The dianion-radical of lophine (2,4,5-triphenylimidazole) has been obtained by reduction of the heterocycle by potassium in DME at low temperature. On warming to room temperature, a diamagnetic product results which, in the presence of an excess of potassium, itself gives a radical which is identified as the dianion-radical (139) of 2-phenylphenanthro[9,10-d]-imidazole 446-448... 

Well resolved EPR spectra of stable dianion radicals of S-diketonate have been observed in the reaction of transition metal / -diketonates of manganese(III), iron(III), cobalt(III) and copper(n) with Grignard reagents . On the basis of the spectral pattern and of... 

Dianion Radicals, Trianion Radicals, and Multianion Radicals... 

Just as the one electron reduction of a neutral molecule produces an anion radical, the one electron reduction of an organic anion can yield a dianion radical, assuming that the LUMO of the anion is not too high in energy. Two anions familiar in organic chemistry are the dibenzoylmethide (an enolate of a 6-diketone) [112] and fluorenide anions [113] (Scheme 68). 

The dianion-radical 170 was prepared by Russell and co-workers, along with several analogs. The proton hyperfine splitting for the 2-position was proved by specific deuteration the other splittings were not assigned. ... 

Compound XXIV is reduced at a more negative potential in a reaction reversible on the time scale of CV, but the dianion radical reacts further on the coulometric time scale. The product distribution is dependent on the pK of the added proton donors. The following scheme is suggested [83] ... 

Attachment to the Carboxylate Group. In basic systems where the amino group is not protonated, attachment occurs on the carboxylate ion, as evidenced from ESR studies on hydroxide glasses (16). At — 196°C spectra are observed for the dianion radical of several amino acids. At higher temperatures, the fatty acid radicals are formed, indicating that deamination has taken place ... 

The product and mechanistic studies of oxidation of important pyrocatechols and hydroquinones by oxygen in an alkaline medium189-19S give information on the types of radical intermediates formed. It was found by means of flow ESR methods196 197 that the radical CXXXVII arises in aquenous alkaline medium in the oxidation of 2-tert-butylhydroquinone CXXXVI, which is one of the most efficient hydroquinone antioxidants. As a secondary radical, the dianion radical CXLI was detected in a static arrangement, which is formed via intermediates... 

CXXXIX and CXL (R = H). The reaction proceeds analogously in aqueous-alcoholic medium (in intermediates CXXXIX and CXL, R = Me or Et). Analysis of ESR spectrum of the secondary radical as well as the model oxidation of 2-tert-butyl-6-hydroxy-hydroquinone CXLII confirmed the structure of the dianion radical CXLI. Also the oxidation of other 2-tert-alkyl-, 2-sec.alkyl-, or 2-n-alkylhydroquinone proceeds by the same mechanism1981. The oxidation can be carried out preparati-vely194,195,198) 2-hydroxy-6-alkyl-l,4-benzoquinonesof type CXLIII are formed in the yield of 65 to 87%. 

The course of oxidation of 4-tert-butylpyrocatechol CXLIV is shown in Scheme 18196 1971. In aqueous medium, the ion radical CXLV and the dianion radical CL which is derived from 2-hydroxy-5-tert-butyl-l,4-benzoquinone CLI are formed. The intermediates are CXLVII and CXLVIII (R = H). The course of oxidation is more complex in an aqueous-alcoholic medium. Formation of 4-tert-butyl-5-methoxy-l,2-benzosemiquinone CIL (R = Me) was found in this case. The oxidation of other 4-tert-alkylpyrocatechols also has an analogous course. In the preparative arrangement of oxidation, 4-tert-alkyl-l,2-benzoquinone CXLVI was not obtained, however, 2-hydroxy-5-tert-alkyl-l,4-benzoquinones of type CLI can be isolated in high yield192-1951. 

Alkoxyazocines exist in tub conformation without conjugative stabilization, but its dianions, obtained by electrochemical or chemical reduction, exist in aromatic planar conformation <71JA16l, 71JA168>. The existence of 3,8-dimethyl-2-methoxyazocine (DMMA) dianion radical (20) along with its electron distribution and thermodynamic stability were reported for the first time in 1983 <83JA6078>. Reduction of DMMA in HMPA with metal sodium or potassium yielded an anion... 

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