Quinone oxygen

Quinones, which become reduced to the corresponding hydroquinones. Two important quinones often used for aromatizations are chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone) and DDQ (2,3-dichloro-5,6-dicyano-l,4-ben-zoquinone). The latter is more reactive and can be used in cases where the substrate is difficult to dehydrogenate. It is likely that the mechanism involves a transfer of hydride to the quinone oxygen, followed by the transfer of a proton to the phenolate ion °... 

Purified ligninase H8 produced by P. chrysosporium in stationary cultures oxidized pyrene to pyrene-1,6- and pyrene-l,8-quinones in high yield, and experiments with showed that both quinone oxygen atoms originated in water (Figure 8.25). It was suggested that initial one-electron abstraction produced cation radicals at the 1 and 6 or 8-positions (Hammel et al. 1986), whereas in... 

However, from the nitrogen content a lower percentage of quinone oxygen was calculated than from the hydrogen uptake during reduction with sodium borohydride. Other double bonds can react with diazomethane as well (74) ... 

There seems to be a ratio of one free radical per quinone oxygen. Donnet et al. (101) concluded that either paraquinones or aroxylic radicals were present, which would react according to the following schemes. 

It is clear that the g values are very sensitive to the presence or absence of hydrogen bonding to the quinone oxygens and to the hydrophobicity of the solvent surrounding or the protein pocket. Also the structure of the quinone itself plays a role.140 However, since the 0-tensor reflects only the global properties of the wavefunction it is still difficult to draw far reaching conclusions from this spectroscopic parameter. This situation will hopefully change when more reliable 0-tensor calculations, e.g. for radicals embedded in proteins, become available, e.g. on the QM/MM level. 

Generation of quinone methides by unmasking a quinone oxygen 57... 

O-Alkylation and O-protonation of the quinone oxygen reactivity effects 69... 

The quinone oxygen of p-1 is weakly basic. Protonation or methylation of this oxygen places a unit positive charge at p- 1-1+ or />-Me-l +, which is highly delocalized through the aromatic ring and onto the benzylic carbon. This... 

The kinetic barriers to organic reactions depend on both the thermodynamic driving force to the reaction (Fig. 3A) and the intrinsic barrier (A, Fig. 3B) to the reaction in the absence of any driving force (Ag° = 0).148 149 The effect of alkylation of the quinone oxygen of quinone methide p-1 and of alkylation of a... 

The formation of the hydrogen bond between the quinone oxygen atom and the amide proton in the reduced form (Fc—Q" ) is observed in photoinduced ET (133). Photoexcitation of the Q moiety in Fc—Q in deaerated PhCN with 388-nm femtosecond (150 fs width) laser light results in appearance of a new absorption... 

An interesting property in connection with these bodies is that only such oxyquinones as have one hydroxyl group in the ortho-position to the quinone-oxygen possess this power of dyeing on mordants, and that in general it is necessary to have simultaneously two hydroxyl-groups in the ortho-position to each other [32, 33]. 

The quinoneoximes closely resemble the oxyquinones in their properties. Only compounds derived from orthoquinones are capable of fixation on mordants. Mono- or dioximes are formed by substitution of one or both quinone-oxygen atoms in an ortho-quinone by the isonitroso-group NOH. 

It differs from fluorescein in containing two quinone oxygen atoms in combination with two benzene rings. 

From these methods of formation it follows that the two quinone-oxygen atoms are in the para position to each other. The quipone reaction can be used in doubtful cases to decide whether a compound... 

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