Dibenzo radical cation

This list includes BP, 7,12-dimethylbenz[a]anthracene, 3-methylchol-anthrene, dibenzo[a,i]pyrene and dibenzo[a,h]pyrene. These PAH can be activated both by one-electron oxidation and/or monooxygenation. There are a few PAH with low IP which are inactive (Table I), such as perylene, or weakly active, such as anthanthrene. This indicates that low IP is a necessary, but not sufficient factor for determining carcinogenic activity by one-electron oxidation. These inactive or weakly active PAH have the highest density of positive charge delocalized over several aromatic carbon atoms in their radical cations, whereas the active PAH with low IP have charge mainly localized on one or a few carbon atoms in their radical cations. 

Figure 8.6 EPR spectrum of the dibenzo[a,e]cyclooctene radical cation showing hyperfine structure. The radical was generated by UV irradiation of the neutral parent molecule. From Gerson, F., Felder, P., Schmidlin, R. and Wong, H. N. C., J. Ghent. Soc., Ghent. Gommun., 1659-1660 (1994). Reproduced by permission of The Royal Society of Chemistry.

An anodic azacyclization, producing tropane-related 11-substituted dibenzo[a,d]cycloheptimines 123, was recently developed by Karady et al. [136, 137]. This two-electron process is initiated by anodic oxidation of the O-substituted hydroxylamine 119 in nucleophilic solvent. It is proposed that the first one-electron oxidation leads to the aminium radical cation 120 which adds rapidly to the double bond. The electron-rich carbon radical 121 is readily oxidized to the carbocation 122. Selective nucleophilic attack on 122 from the less hindered exo-side yields the 11- substituted product 123. Depending on the... 

Small changes in the solvent or in the conditions of oxidation can lead to changes in the electronic and molecular structure of aryldiazo radical cations, from a linear allylic 7T- to a bent a-radical state. Both states have been observed in the radical cations of diphenyldiazomethane (49) and 5-diazo-10,ll-dihydro-5//-dibenzo[a, /]cycloheptene... 

The structures of the radical anion of dibenzo[a,c]naphthacene (135) and the corresponding radical cation were investigated by ESR and proton-ENDOR spectroscopies. ... 

Mass spectra of the dibenzo-l,2-dithiins 52 and S3 display intense parent ions, indicating that loss of an electron gives rise to particularly stable radical cations <2000JA5052>. 

The phenomena enumerated in Section 2.4 do not, of course, fully describe all the differences between chemical and electrode processes of ion radical formation. From time to time, effects are found that cannot be clearly interpreted and categorized. For instance, one paper should be mentioned. It bears the symbolic title ir- and a-Diazo Radical Cations Electronic and Molecular Structure of a Chemical Chameleon (Bally et al. 1999). In this work, diphenyldiazomethane and its 15N2, 13C, and Di0 isotopomers, as well as the CH2-CH2 bridged derivative, 5-diazo-10,ll-dihydro-5H-dibenzo[a,d]cycloheptene, were ionized via one-electron electrolytic or chemical oxidation. Both reactions were performed in the same solvent (dichloromethane). Tetra-n-butylammonium tetrafluoroborate served as the supporting salt in the electrolysis. The chemical oxidation was carried out with tris(4-bromophenyl)-or tris(2,4-dibromophenyl)ammoniumyl hexachloroantimonates. Two distinct cation radicals that corresponded to it- and a-types were observed in both types of one-electron oxidation. These electromers are depicted in Scheme 2-28 for the case of diphenyldiazomethane. 

It has been shown voltammetrically that oxidation of 1,4-dioxin and of its 2,3,5,6-tetraphenyl, benzo, and dibenzo derivatives takes place at a rotating platinum electrode in acetonitrile in single-electron steps with the intermediate formation of radical cations.The simplest dioxin cation-radical for which an ESR spectrum has been obtained is 79, for which hyperfine splittings are indicated in gauss.The radical was prepared by treatment with sulfuric acid of the dimer which forms spontaneously on the storage of acetoin. 

Under conditions that are not strictly nonaqueous, the oxidized dimer may be trapped by water, as was observed during the oxidation of 1,1-diphenylethylene catalyzed by the radical cation of dibenzo-1,4-dioxin [91]. The dimer dication upon reaction with water undergoes a 1,2-phenyl shift, resulting finally in 1,2,4,4-tetraphenyl-3-buten-l-one [Eq. (42)], reminiscent of the 1,2-shifts observed during anodic oxidation of 1-phenyl- and 1,4-diphenylnaphthalene in acidic dime thy Iformamide (DMF) [92]. 

Similarly to tetrathioethylenes and tetrathiafulvalenes, 1,4-dithiin (LV) and its benzoder-ivatives (LVI and LVII) are electron-rich compounds that can be easily oxidized to their corresponding cation radicals and dications. There are several reviews [2, 3, 186, 187] on the chemistry of the radical cations of dibenzo-1,4-dithiin (LVH) and related compounds. 

The trimethylsilyloxy (TMSO) group is stable under the coupling conditions in acetonitrile (Table 4, number 11). After oxidative dimerization the TMS ether can be mildly hydrolyzed (H and H2O) to the phenol or converted to a dibenzofuran. 1,2-Dialkoxybenzenes have been trimerized to triphenylenes (Table 4, numbers 9, 12, and 13). The reaction product is the triphenylene radical cation, which is reduced to the final product either by zinc powder or in a flow cell consisting of a porous anode and cathode [60]. Dibenzo-crown ethers are converted by anodic oxidation to electroactive polymers. Films of these polytriphenylenes exhibit unusual doping properties 62-64]. 

Some substituted dibenzo-7-silabicyclo[2,2,l]hepta-2,5-dienes are reported to phototransfer an electron to TCNE using 2,4,6-triphenylpyrylium tetrafluoro-borate as sensitizer to give difluorosilane and anthracene as products. The MOP AC MP3 method has been used to examine the electronic features of the radical cation of the parent silane. 

Among the reactions of 1,4-dioxins and 1,4-dithiins, oxidation of their tetraphenyl and dibenzo derivatives is important. This reaction leads to the formation of radical cations 7 and dications 8... 

The electrochemical oxidation of dibenzo(c,e)-l,2-diselenine 89 to its radical cation and further transformations have been described (Scheme 20) <1996JEC183>. In wet acetonitrile the oxidation has been shown to take place in two steps, the first an oxidation to the selenoxide followed by a further oxidation with extrusion of selenium dioxide to afford the corresponding selenophene <1992MI2077>. 

The oxidation of 89 has been studied in dry acetonitrile using both conventional and microelectrode techniques <19%JEC183> and the results compared with those for its isomer selenanthrene. This study confirmed that radical cation reactivity in the case of the 1,2-dibenzo diselenins is greater than that of the 1,4-dibenzodiselenins. This difference in reactivity has been explained by the existence of a three-electron selenium-selenium bond in the case of the radical cation of the 1,2-dibenzodiselenin, 90. This bond is a ofp-p) bond with the additional electron promoted into the corresponding radical cation of 1,4-dibenzodiselenin, 91. 

This color transformation has been observed in dibenzo-p-dioxin (Structure I) and in its bromo, chloro, nitro, methyl, and ethyl derivatives in addition, the observed electron spin resonance (ESR) signals indicated the presence of paramagnetic species (2, 3). This phenomenon has been attributed to the formation of cation radicals in acid solution. 

Studies were made on a series of chlorinated dibenzo-p-dioxin cation radicals in trifluoromethanesulfonic acid (TFMS acid). TFMS acid was... 

The 1-chloro- and 2-chlorodibenzo-p-dioxins, which readily dissolved in TFMS acid, formed cation radicals without UV irradiation or the addition of oxidizing agents. With the exception of broader resonance lines. Figure 3 shows that the five-line pattern observed with 1-chloro-dibenzo-p-dioxin is similar to that of the unsubstituted dibenzo-p-dioxin. Apparently, protons at the 2, 3, 7, and 8 positions became less equivalent... 

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