Quinone-like

The photolysis of arenediazonium salts has been widely used for intramolecular cyclizations in the synthesis of 1-phenylethylisoquinoline alkaloids by Kametani and Fukumoto (review 1972). An example is the photolysis of the diazonium ion 10.73, which resulted in the formation of O-benzylandrocymbine (10.74) (Kametani et al., 1971). The mechanism of this cyclization is obviously quite complex, since the carbon (as cation or radical ) to which the diazonio group is attached in 10.73 does not react with the aromatic CH group, but with the tertiary carbon (dot in 10.73), forming a quinone-like ring (10.74). In our opinion the methyl cation released is likely to react with the counter-ion X- or the solvent. 

Attempts of further nitration of dinitro derivative 83 under usual conditions failed. Using 100% nitric acid in fluorosulfonic acid or trifluoromethanesulfonic acid, reagents useful for nitration of deactivated aromatic systems led to the formation of moisture-sensitive nitration products, which undergo further oxidation to give o-quinone-like species 84 and 85. Using the latter conditions, compound 86 can be isolated in 20% yield and converted into the tetraoxo derivative 85 by heating at 220°C (Scheme 4) <1996JOC1898>. 

The nitration of the polyheterocyclic compound 226 leads to the formation of moisture-sensitive nitration products, which undergo further oxidation to give o-quinone-like species (Scheme 55) <1996JOG1898>. 

If the position para to the NHOH-group is occupied, as, for example, in p-tolylhydroxylamine, the catalytic action of strong acids produces a different result. The hydroxyl group is indeed shifted to the carbon atom in the p-position, but this leads to the production of a quinone-like substance ... 

Yield.—Almost theoretical (10 gms.). Lustrous green prisms or leaflets quinone-like odour soluble in warm petroleum ether insoluble in cold water M.P. 171°. (B 24, 1341 28, 1615.)... 

Irradiation of commercial shrimp in which melanogenesis had begun accelerated the reaction. It was postulated that the quinone-like end products of the reaction sequence acted as competitive inhibitors for the reaction and also functioned as radiation protectors for the enzyme. Subsequent irradiation would destroy the capacity of the end products to inhibit the reaction and simultaneously preserve the enzyme activity, thus accelerating further melanogenesis. 

A variant on iodine deprotections is a report on the cleavage of PMB ethers by a mixture of cerium(III) chloride heptahydrate and sodium iodide in refluxing acetonitrile.210 A proposed mechanism involves polarization of the ethereal link (158, Scheme 43), followed by generation of a quinone-like species, and attack by nucleophilic iodide to afford p-methoxybenzyl iodide. 

The most serious toxicities associated with carbamazepine use are idiosyncratic skin rashes, hematological disorders, hepatotoxicity, and teratogenicity (80). On the basis of studies with mice, teratogenicity is most likely related to formation of arene oxide and/or quinone-like metabolites of carbamazepine (83),... 

Benzofurotropylium salts (cf. Section II,C,3,a) that bear a hydroxyl group at C-3 (e.g., 611) are deprotonated to yield mesomeric furo-p-benzoquinonetropides or tropylidene quinones like 613 [67BGJ1480 71JCS(P1)2399]. 

Mn(III) complex for the solution represented by curve C. Apparently, the excess K3Fe(CN)6 oxidizes the free ligand in the solution, and this in turn is catalytically reduced by the reduced form of the Mn(III) complex. Because of the presence of quinone-like materials in photosystem II (2), this represents a model that warrants additional study. 

Hydrogenation of multiple bonds, like C=C, C=0, C=N, C=S, N=N, C=C, N=N, and bonds in NO and NO2, bonds in quinones and quinone-like structures and in aromatic rings are often followed in protic media. Under such conditions such reductions often involve a proton transfer, either preceding or following the electron transfer. 

As we have already seen these lone pairs can form part of the system of n electrons. The difference between chromo-phoric and auxochromic groups is in this way of secondary importance. Also the much discussed question whether a ben-zoid (benzene-like) or a quinonoid (quinone-like) structure should be attributed to dyestuffs becomes, in the light of the resonance theory, an incorrectly chosen alternative. It is the possibility of resonance which is reflected in the multiplicity of the valence structure that forms the true basis for light absorption. An isolated benzoid configuration is just as little a colouring matter as a quinonoid structure compare the uncoloured hydroquinone and the very weakly coloured quinone. 

In the undoped state, PAni is a base. Three molecular structures are possible, one of them being the so-called emeraldine base (EB) shown in Fig. 1 of Chapter 11 [52]. There are several differences between it and the other CP chains discussed above Due to the presence of the N atoms, the chain has a zigzag shape and the benzene rings have either a benzene-like or a quinone-like bond pattern (see Chapter 11, Section IV.B.l) and may be twisted. In principle, the number of independent structural parameters is even larger than for the other CPs. However, quite a good (albeit partial) understanding of the structure has been achieved, as shown in Ref. 24, for instance. 

Chemical Attachment. The initial step in chemically attaching enzymes to electrodes involves an activation (derivatization) of the support to introduce appropriate functional groups, such as carboxy, phenol, and quinone-like structures. This step is critical and must be controlled rigorously since the greater the number of functional groups, the higher will be the amount of immobilized enzymes attched and the better the final electrode activity. The electrode surface may be activated by different ways ... 

The quinone-like carbonyl groups have received considerable attention in several electrochemical studies (L5, 21). Such... 

The most characteristic feature of quinones is their ease of reduction and reoxidation they play a part in the redox processes of many living systems (22). Furthermore, they can interact with amino and sulfhydryl groups. One might therefore expect quinone-like groups to participate in protein adsorption and perhaps cell adhesion although no direct evidence is available to support this hypothesis. Studies of quinone-like groups on activated carbon surfaces (23) indicate such groups can participate as electron donors in donor-acceptor complexes with adsorbed molecules (17, 24). 

Table IV summarized the ESCA data obtained on the polished carbon surfaces along with estimates of percentages of the carbon-oxygen groups on the surface. Roughly 85-90% of both the unalloyed and Si-alloyed carbon surfaces are shown to be oxygen-free, with the remainder consisting of three major types of oxygen-containing functional groups approximately 60% are of the ether-like variety, 25% are quinone-like, and the remaining 15% are ester-like.

The data also correlate with the electrochemical investigations of Epstein, et al., ( ), i.e., that quinone-hydroquinone groups are most likely present on LTI carbon surfaces. They further concluded that such groups can be readily converted electrochemically from one to the other. As previously noted, our data indicates that approximately 25% of the surface oxygen is quinone-like in nature. 

Pyrolytic Carbon. Polished LTI carbon is composed of a crystalline graphitic-like microstructure, combined with amorphous material ( ). The polished samples have been shown to be oxidized with a C 0 ratio of about 10 1, containing three major types of carbon-oxygen functionalities quinone-like, ether-... 

Electrochemical studies of carbon samples have shown that both quinone-like and ester-like groups are present (18). 

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