Semi-quinone derivative

In Figure 1, the peaks with intensity greater than 25% of the largest peak were identified as PAHs, with the exception of the peak at scan 1275. This peak was identified as 1-nitropyrene. The methylene chloride fraction was considerably more complex and included primarily carboxaldehyde and semi-quinone derivatives of PAH. The largest peak (scan 850) was identified as 9-fluorenone. 

Allyl (27, 60, 119-125) and benzyl (26, 27, 60, 121, 125-133) radicals have been studied intensively. Other theoretical studies have concerned pentadienyl (60,124), triphenylmethyl-type radicals (27), odd polyenes and odd a,w-diphenylpolyenes (60), radicals of the benzyl and phenalenyl types (60), cyclohexadienyl and a-hydronaphthyl (134), radical ions of nonalternant hydrocarbons (11, 135), radical anions derived from nitroso- and nitrobenzene, benzonitrile, and four polycyanobenzenes (10), anilino and phenoxyl radicals (130), tetramethyl-p-phenylenediamine radical cation (56), tetracyanoquinodi-methane radical anion (62), perfluoro-2,l,3-benzoselenadiazole radical anion (136), 0-protonated neutral aromatic ketyl radicals (137), benzene cation (138), benzene anion (139-141), paracyclophane radical anion (141), sulfur-containing conjugated radicals (142), nitrogen-containing violenes (143), and p-semi-quinones (17, 144, 145). Some representative results are presented in Figure 12. 

Besides potential pharmacological applications, a number of other uses have been described for phenoxazine derivatives. The semi-quinone radical obtained on oxidation of phenoxazine with various oxidants, which has been shown to give a characteristic absorption at about 530 mp., was used by Sawicki et al.110 in a new method for the spectrophotometric determination of nitrite the aqueous nitrite sample is treated with a 0.1% solution of phenoxazine in glacial acetic acid and the absorbance is read at 530 mp. 

If the original semiquinone radical QH is polarized, the semi-quinone radical anion derived from eq. 52 can be expected to retain much of the initial polarization. Thus in the CIDEP studies of the photoreduct ion of quinones in triethylamine solution, the primary photochemical process was thought to involve the possible exciplexes (42) ... 

The antioxidant activity of phenol is also increased by the presence of additional hydroxyl group in the ortho or para positions. An example of such an antioxidant is TBHQ. The effectiveness of 1,2-dihydroxybenzene derivatives is attributed to a phenoxyl radical stabilised by an intramolecular hydrogen bond (11-8). The activity of 2-methoxyphenol is lower, because the generated radical cannot be stabihsed by a hydrogen bond. The antioxidant activity of 1,2-and 1,4-dihydroxybenzene is partly caused by the fact that the semi-quinone radical can be further oxidised to the corresponding o-quinone orp-quinone, respectively, by reaction with another lipid radical (Figure 11.7) or may disproportionate to the corresponding quinone and hydroquinone. 

Semi- carbazone Oxime Hydro- quinone DIacetate of hydro-quinone Thiele acetylation product Other Derivatives... 

Contrary to the naphthazarin case, dihydroxyanthraquinones (QH2) form semi-oxidised quinones which undergo simple bimolecular disproportionation to the diquinone and parent quinone [74]. Both the above reactions have been wrongly given due to printers devil type error m a recent review [12]. The pK for the semi-oxidised anthraquinone derivatives was measured and shown to be around 8. 

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