Quinonoid Structure Research Articles

Novel diphenoquinone-type redox systems containing seven-membered quinonoid structure

5-(3,5-Di- t-butyl-4-hydroxyphenyl)tropolone ( 5 ) and 5,5′-bitropolone ( 7 ) were synthesized using transition-metal-catalyzed coupling reactions. Oxidation of 5 afforded the diphenoquinone-type trione ( 6 ); however, 7 could not be converted into 8 . The quinonoid character of 6 is discussed on the basis of the electrochemical redox behavior.

Studies on fluorescein—III: The acid strengths of fluorescein as shown by potentiometric titration

Potentiometric back-titration of yellow solid fluorescein (H 2Fl) and of red solid fluorescein in alkali with acid yielded titration curves that were practically identical in shape and position. The end-points at pH 8.5, 5.40 and 3.3 corresponded, respectively, to titration of the excess of standard alkali, and the successive protonations Fl 2− + H + = HFl − and HFl − + H + = H 2Fl. The pH at the mid-point of the first protonation yielded a value of 6.36 for p K HFl (ionic strength 0.10). Because of precipitation of yellow fluorescein during the second protonation step, a value for p K H 2Fl could not be obtained. The total concentration of fluorescein at the first appearance of the precipitate fell on the curve for the solubility of yellow fluorescein as a function of pH. The titrations and the p K values found for the three acid groups of protonated fluorescein (H 3Fl +) have been interpreted on the basis that in water fluorescein exists in only one structural form the yellow zwitterion. Similar back-titrations of alkalinized solutions of yellow or red fluorescein in 50% aqueous ethanol showed that in this medium fluorescein is present in only one form, presumably the quinonoid structure, with much weaker apparent acid functions, p K' 1 = 6.38 and P K' 2 = 7.16 (ionic strength 0.10).

Cage ketones from dimethyl-1,4-benzoquinones and quinonoid carbanions ; A charge-transfer controlled synthesis

3-Methyl-1,4-naphthoquinon-2-ylmethyl anion ( la ) adds 2,6-dimethyl-l,4-benzoquinone reversibly giving, in addition to products of types already known, a derivative ( 2 ) of the cage hydrocarbon decahydro-4,l,7-ethanylylidene-naphthalene which can be obtained as the major product. A similar reaction with 2, 5-dimethyl-l,4-benzoquinone gives a similar cage compound ( 3 ) but derived from decahydro-8,2,5-ethanylylidenenaphthalene ( 14 ), a member of the twistane series. This reaction can be modified to yield the more complex cage compound ( 4 ) derived from the hydrocarbon tetradecahydro-5,8,9,10-[l,2,3,4] butatetraylanthracene. Since the only anions that initiate cage formation in benzoquinones have themselves quinonoid structures it is suggested that charge-transfer complexation aligns the interacting rings and promotes reversibility in Michael reactions, thus allowing steric repulsions to control the regiospecificity.

キノノイド構造を有する拡張環状交差共役系の化学

One of the recent advances in the field of non-benzenoid aromatics would be the chemistry of the extended cyclic cross-conjugated compounds derived by insertion of more complex conjugated π-electron system instead of the exo-double bond in fulvene-, fulvalene-, annulenone-, and oxocarbon-systems. Many physical and chemical properties of remarkable interest have been developed in these newly designed cross-conjugated variations. The present review deals with the chemistry of quinarenes, quinarenones, quinocarbons, and their hetero analogs which are the extended cyclic cross-conjugated π-electron systems comprising one or more quinonoid structures. The fundamental insights mentioned here would provide helpful suggestions for the molecular design of organic dyes, highly polarized compounds, electron acceptors or electron donors having a bright prospect of developing the new field of application to the optoelectronics, organic super conductors, and so on.

SYNTHESIS AND PROPERTIES OF 7-(2,3-DIPHENYLCYCLOPROPENYLIDENE)-1,6-METHANO-2(7H)-[10]ANNULENONE. A [3.10]QUINAREN-5-ONE DERIVATIVE HAVING POLYOLEFINIC CHARACTER

Abstract The title quinarenone 2 in which the electron donating and electron accepting groups are located at the separate sites bisected by the 1,6-methano bridge, has been prepared. This compound has a preferable contribution of quinonoid resonance structure 2a to dipolar structure 2b in the ground state in order to maintain the weak conjugation between the two terminal chromophores, steming the C-1,6 overlap.

Oligocyclic Hetarenes with Quinonoid Structure; Synthesis by Sequential Cyclizing Condensation

Oligocyclic Hetarenes with Quinonoid Structure; Synthesis by Sequential Cyclizing Condensation

Aqualuminescence from γ-irradiated NaCl in the presence of dye lasers

It is well known that the dissolution of γ-irradiated alkali halides in water results in the emission of light. An enhancement in aqualuminescence has been observed for water doped with the popular dye lasers Rhodamine B and 6 G. Emission spectra of the aqualuminescence were recorded on a Fuoss spectrograph. The mechanism of light emission is explained on the basis that reaction between e aq − with dye lasers results in the formation of excited species possessing the quinonoid structure.

EI/CI mass spectra and the oxidation products of dobutamine under storing conditions

Dobutamine dissolved in different water and alcohol solutions produced a black precipitate at a rate dependent on the amount of dissolved oxygen. The precipitate is shown to consist mainly of compounds C 18H 19NO 3 (m/z 297) and C 18H 19NO 4 (m/z 313) both with a ketimine function in bridge between the aromatic rings and with a different quinonoid structure at the catechol end.

SYNTHESIS AND PROPERTIES OF 5-(1,3-DITHIOL-2-YLIDENE)-2(5H)-THIOPHENONE

Abstract The title compound and its phenyl derivatives have been prepared by the advantageous route which we have developed. These cross-conjugated compounds are suggested to have a preferable contribution of the quinonoid resonance structure at the ground state, but are slightly more polar than the iso-π-electronic 5-cycloheptatrienylidene-2(5H)-thiophenone, revealing that the dithiolidene residue is more electron-donating than the cycloheptatrienylidene one.

Resonance Raman spectra of phenoxy and monosubstituted phenoxy radicals

AbstractThe resonance Raman spectra of the phenoxy radical and its deuterated species have been observed. The characteristic features of the spectra have been interpreted on the basis of a large contribution from a quinonoid type resonance structure. The assignment of each band is discussed. The effects of ortho and para substitution on the Raman spectra are also discussed.

Pterins. Part 9. The structure of quinonoid dihydropterins [2-amino-7,8-dihydropteridin-4(6H)-ones

A comparative study of the rates of oxidation of 2-amino-cis-6,7-dimethyl-5,6,7,8-tetrahydropteridin-4(3H)-one (6), its 2-methylamino (7), 2-dimethylamino (8), 8-methyl (9), and 3-methyl (10) derivatives, and their 6,7-dideuterio-derivatives by molecular oxygen to the corresponding quinonoid 7,8-dihydro-6H-pterins, the rates of rearrangement of these to the respective 7,8-dihydro-3H-pterins, and the reduction of these quinonoid dihydropterins by NADH in Tris chloride buffer at pH 7.6 and 25° are reported. These data together with the lack of significant u.v. spectral shifts in the bands of the transient spectra of quinonoid 7,8-dihydro-6H-pterin, its 6-methyl and 2-dimethylamino-6,7-dimethyl derivatives in buffers between pH 6.8 and 11.6 strongly support the ‘ortho’ quinonoid dihydropterin structure (3) over the ‘exocyclic para’ quinonoid (2) and ‘endocyclic ortho’ quinonoid (4) structures. A mechanism whereby hydride from NADH is transferred to N(5) and a proton to N(3) of quinonoid dihydropterin substrates in the enzymic reduction by dihydropteridine reductase is proposed.

Resonance Raman spectra for flavin derivatives modified in the 8 position.

Spontaneous resonance Raman or resonance-enhanced AC-coupled inverse Raman spectra were obtained for 8-mercaptoriboflavin, 8-(dimethylamino) riboflavin, 8-hydroxyriboflavin, and 8-aminoriboflavin all free in solution. These Raman spectra were all similar to one another and markedly different from that of riboflavin. In addition, the Raman spectra of 8-mercaptoflavin bound to the apoproteins of old yellow enzyme, glucose oxidase, and L-lactate oxidase were determined. The Raman spectra of these protein-bound flavins were distinctly different from both those of the above 8-substituted riboflavins and that of riboflavin. An argument is presented in favor of assigning a quinonoid electronic structure to these protein-bound flavins.

Langlebige α-metallierte methylradikale und deren dimere

Persistent radicals R' 2C .MR 3(I), R'C .(MR 3) 2 (II) and RC???(MR 3)OMR 3 (III), R'  mostly Ph but also t-Bu, H, R' 2  also 9-fluorenyl or 9-xanthenyl, M  Si, Ge, Sn, have been generated from the corresponding CH or CHal compounds or by addition of R 3M . to ketones. Radicals I, II and III are investigated by ESR spectroscopy. A temperature-dependent equilibrium has been found between these radicals and their dimers (IV), of, as far as investigated, quinonoid structure. Dimers IV rearrange with acids giving diaryl methanes. Autoxidation of radicals I at 80°C gives the benzpinacol derivatives, whose radicals are oxidized again, undergoing different fragmentations. At room temperature, however, the dimers IV are attacked by O 2 forming the metalated benzophenone derivatives via fragmentation, which are split by UV light into the radicals R 3M . (M  Si, Ge, Sn) and the oxyl radicals, which are highly stabilised by mesomerism.

Specificity of antisera to oestrogen-azo-protein conjugates: The influence of tautomerism and carrier proteins

A hypothesis is presented to account for the puzzling nonspecificity toward the A ring and for slow immune response to oestrogen-4(2)-(4'-carboxyphenylazo)- or 4(2)-azoprotein conjugates which has been described in the literature and was also found in our laboratory. The phenomenon is associated with the presence of tautomeric forms of haptens in the conjugates. High cross-reactivity of antisera to these haptens with C-3 derivatives of the oestrogens and with substances structurally related to their quinonoid forms is explained by the existence of the internal hydrogen bond in o-hydroxyazo-conjugated steroids and by conversion of these haptens to quinonoid structures. The influence of the carrier protein and of the mode of immunization on the proportions of the two tautomeric forms in the conjugates is discussed.

The reaction of t-butyl chloride with “living” poly-α-methylstyryl sodium in tetrahydrofuran

The solid reaction products obtained from the reaction between α-methylstyryl sodium “living” ends in tetrahydrofuran with t-butyl chloride, at ambient temperatures, have been separated by TLC and examined by UV, IR and NMR spectroscopy. Apart from the expected elimination and substitution products, a new grouping, absorbing UV radiation at 315 nm. is found in the polymer. IR and UV data suggest that the new grouping is of a quinonoid type structure. Several mechanisms, in explanation of the overall reaction, are discussed in the light of these results.

Biopterin. V. De novo synthesis of dihydrobiopterin: evidence for its quinonoid structure and lack of dependence of its reduction to tetrahydrobiopterin on dihydrofolate reductase.

AbstractSamples of quinonoid‐l‐erythrodihydrobiopterin (q‐BH2) and quinonoid‐6‐methyl‐dihydro‐pterin (q‐6‐MPH2) were prepared by oxidation of l‐erythro‐5,6,7,8‐tetrahydrobiopterin (BH4) and 5,6,7,8‐tetrahydro‐6‐methylpterin (6‐MPH4) and separated from D‐erythro‐7,8‐dihydrobiopterin (7,8‐BH2) and 6‐methyl‐7,8‐dihydropterin (7,8‐6‐MPH2) as well as from the tetrahydropterins on phosphocellulose column by high‐pressure liquid chromatography. The quinonoid dihydropterins were identified and quantitated by scan of their ultraviolet absorption and fluorescence emission spectra through their rearrangement to their 7,8‐tautomer and also by gas chromatography of their rapidly synthesized trimethylsilyl derivative. Identification was also achieved by the enzymatic reduction of [3H]q‐BH2to [3H]BH4 by dihydrofolate reductase (DHFR). Direct proof for the enzymatic synthesis of the q‐BH2 from GTP or from 2‐amino‐6‐(5′‐triphosphoribosyl)‐amino‐5‐ or ‐6‐formamido‐6‐hydroxypyrimi‐dine (FPyd‐P3) was obtained by isolation of the compound which was identical in all respects to the q‐BH2 obtained by chemical synthesis from BH4. The reduction of enzymatically synthesized q‐BH2 by dihydropteridine reductase (DHPR) to BH4 was not inhibited by methotrexate (MTX). When the enzymatically synthesized q‐BH2 was converted to 7,8‐BH2, it was reduced only by DHFR. This reduction, however, was inhibited by MTX. On the biosynthetic pathway from GTP to dihydrobiopterin, the enzyme responsible for the appearance of the quinonoid structure is the d‐erythro‐dihydroneopterin triphosphate synthetase, the product of which (quinonoid d‐erythro‐dihydroneopterin triphosphate) is converted to quinonoid dihydrobiopterin by l‐erythro‐dihydrobiopterin synthetase. Experiments in vivo established that DHFR does not participate in the reduction of dihydrobiopterin to tetra‐hydrobiopterin when the former is synthesized from GTP de novo. MTX at 5 × 10−6M exerted no inhibition on the reduction of the biosynthetic dihydrobiopterin to tetrahydrobiopterin in vivo, yet completely inhibited the reduction of intraventricularly injected tritiated dihydrofolate ([3H]FH2) to tritiated tetrahydrofolate ([3H]FH4).

The crystal and molecular structure of (4-diethylaminophenyl)diazenyltriphenylphosphonium tetrafluoroborate

The title compound crystallizes in the space group P21/c with four formula units in a cell of dimensions a = 10.146(6) Å, b = 10.593(4) Å, c = 26.31(1) Å, β = 103.14(3)°. Using 1496 observed reflections (I = 2.3σ(I)) in the range 0° < 2θ < 40° measured on a Picker FACS-1 automatic diffractometer with Mo-Kα radiation, the structure was solved (symbolic addition) and refined (full-matrix least-squares procedure) to R = 0.062 (Rw = 0.058), with all hydrogen atoms included and all non-hydrogen atoms having anisotropic thermal parameters. The dimensions within the cation are consistent with a delocalized electronic structure which is intermediate between valence formulations involving benzenoid or quinonoid structures for the (4-diethylaminophenyl)diazenyl residue. Some important bond lengths are N3—C22 1.336(7) Å, N2—C19 1.356(7) Å, N1—N2 1.308(6) Å, and P—N1 1.648(5) Å.

Tricyclic Isoindoles

Isoindoles with annelated rings, e.g. (1) and (2), X = SO2CH3, are remarkably stable compared to the parent compound. Tautomeric forms of (1) with benzenoid or quinonoid structure could not be detected.

Heterocycles by cycloaddition. Part II. Cycloaddition–extrusion reactions of five-membered mesoionic compounds with benzyne: prepartion of benz[c]azole and benzo[c]thiophen derivatives

Several five-membered mesoionic compounds react with benzyne to give benzo-fused five-membered heterocycles [(2) and (5)] with a formal quinonoid structure. A bridged intermediate adduct (4c) was isolated from the reaction of benzyne with a mesoionic thiazol-4-one (3c). Pyrolysis of the adduct gave an isobenzothiophen (5a), whereas its photolysis led to an isoquinolone (7). The corresponding adduct S-oxide (4e) gave the isoquinolone (7) by both pyrolysis and photolysis.

Condensation between 2-chloro-3H-indol-3-one and phenols

2-Chloro-3H-indol-3-one condenses with some phenols having only one reactive position to give quinonoid dyes of the type previously described by Friedlaender. Of the two possible tautomeric forms of these dyes, the quinonoid structure is preferred on the basis of u.v. and n.m.r. spectroscopy and the Michael addition reaction with acetone. The ortho-quinonid dyes show intramolecular hydrogen bonding and are decomposed by alkali to give anthranilic acid and a 2-hydroxybenzaldehyde. The aldehyde recovered from this reaction in deuterium oxide has the aldehydic hydrogen atom replaced by deuterium. The para-quinonoid dyes are protonated by strong acids on the quinonoid oxygen atom and reaction with alkali causes opening of the heterocyclic system to give a benzil, which rearranges.