Oxidation to Radical Cations

According to Stade electrolytic oxidation of l.l-dimethoxy-2.4.6-triphenyl-X -phosphorin 193 with tetra-n-propylammonium perchlorate serving as the electrolyte leads to the formation of a X -phosphorin radical cation 194 which is stable for several hours. Other l.l-hetero-X -phosphorins can be oxidized in the same manner to radical cations 

Oxidation with mercuric acetate, lead tetrabenzoate, lead dioxide in the presence of 2.4.6-triphenylphenol or other oxidizing agents usually does not give the radical cation of 2.4.6-triphenyl-X -phosphorins, but rather the radical cation of 

6- triphenyl-X -phosphorin. The same holds for l.l-dimethoxy-2.4.6-tri-tert-butyl-X -phosphorin which is transformed easily to 2.4.6-tri-tert-butyl-X -phosphorin radical cation. Apparently the X -phosphorin-radical cation easily splits off either the oxygen- or nitrogen-containing substituents to form the very stable, well-known 

6- triphenyl-X -phosphorin or the 2.4.6-tri-tert-butyl-X -phosphorin-radical cation respectively (see p. 41), 

Similarly, with l.l-dimethoxy-2.4.6-triphenyl-X -phosphorins we could observe first the ESR spectrum of the X -phosphorin radical cation 194,ap = 18 Gauss, then, on further oxidation, a new ESR spectrum with flp = 20.8 Gauss and finally the ESR spectrum of the X -phosphorin radical cation 38 withOp = 23.4 Gauss. 

---

In carboxylic acids with an aromatic group or a double bond the ii-systems can be oxidized to radical cations that react with the carboxyl group to lactones (Eqs. 7, 42) [142, 351]. 

The first structure type to be established for a hexadiene radical cation was one in which cleavage is achieved without bonding, i.e. a representative of the dissociative mechanism. Dicyclopentadiene and several derivatives can be oxidized to radical cations (137) in which one of the bonds linking the monomer units is cleaved. The unique spin density distribution of 137 is reflected in an unmistakable polarization pattern [386-389]. 

Tetraphenylethylene cyclizes anodically to 9,10-diphenylphenanthrene analogously to its photooxidative cyclization. The attempted anodic cyclization of cis- or frans-stilbene to phenanthrene however failed due to electrophilic reaction of the intermediate radical cation with the solvent 37S Primary aromatic amines are oxidized to radical cations which, depending on the pH of the electrolyte couple to aminodiphenylamines (C-N coupling (84) in Eq. (172) ), yield benzidines (85) at low pH (C-C coupling) or dimerize to hydrazobenzene (86) (N-N coupling) which is subsequently oxidized to azobenzene (Eq. (172) ) 2 5,376,377)... 

Tetrakis(dimethylamino)ethylene (TKDE) is a strong electron donor which oxidizes to radical-cation and dication states similar to the well-known Wurster s radicals. Cyclic... 

Cavalieri and coworkers, following earlier investigators , have championed the hypothesis that the covalent binding of polycyclic aromatic hydrocarbons to DNA is due to radical cations formed from them by the action of cytochrome P450 and/or peroxidase enzymes . They have reported that polycyclic aromatic hydrocarbons with ionization potentials below 7.35 eV can be oxidized to radical cations by peroxidases . Furthermore, the formation of a benzo[a]pyrene-DNA adduct consistent with oxidation of the... 

Closed shell metalloporphyrins such as those having divalent ions (e.g., magnesium or zinc) readily undergo oxidation to radical cations/ These closed shell ionic metalloporphyrins can be considered to be porphyrin dianions, and therefore they are oxidized more readily than are the free porphyrins themselves. The redox potentials of metalloporphyrins increase with increasing electronegativity of the metal ion. Metalloporphyrins with trivalent or tetravalent metal ions are particularly difficult to oxidize because of the high electropositive character of the metal center. 

Since carbazole groups undergo relatively facile electrochemical oxidation to radical cations, which show an inclination to dimerization, the crosslinked structure (17a) can be easily obtained from carbazole-containing polysiloxanes [189]. The electrochemistry of immobilized dicarbazolyl groups forms the basis for a novel electrochromic display the oxidized film is green in colour, and colourless when reduced. 

---