Hydrogen and electron transfer in the photoreduction reaction of quinones

The primary products of the photoreduction reaction of 3,6-dit-butyl-o-quinone in single crystals of 3,6-di-t-butyl-pyrocatechol are studied by EPR spectroscopy. Ion radical and neutral radical pairs are identified distinctly. In the case of the same o-quinone in single crystals of 2-6-dit-butyl-4-methylphenol the primary product is the radical pair composed of the two hydroxyphenoxyl radicals of phenol. This indicates the possibility of transfer of two hydrogen atoms in a single elementary photochemical event.     

Formation and stabilization of radical pairs in the quinone-pyrocatechol-polymer system

The formation of radical pairs (RP) in solid mixtures of 3,6-di-tert-butyl-o-quinones (Q) and 3,6-di-tert-butylpyrocatechol (QH₂) under the action of shock-wave (SW) pulses was studied by ESR and IR spectroscopy. The radical pairs are formed only when a threshold value of SW power is achieved. The generation of RP is preceded by the formation of hydrogen-bonded associates QH₂…Q upon intimate mixing and fine dispergation of the reagents in a SW field. The incorporation of the reagents into a polymeric matrix favors the formation of associates and stabilization of the pairs, which leads to a decrease in the SW power threshold. Deceased. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1464–1467, August, 1997.     

ESR analysis of the kinetic alkalinity of pseudophedrine

The kinetics of protonation of pseudoephedrine by 3,6-di-tert-butyl-2-hydroxyphenoxyl have been analyzed by the ESR technique. It was shown that protolysis of the radical produced closed ionic pairs with the pseudoephedrine cation in a dimer state.A. N. Nesmeyanov Institute of Elementoorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 2007–2011, September, 1992.     

The mechanism of formation of free-radical states upon the pulsed action of elastic waves on solid mixtures of donor-acceptor compounds

The action of a pulse of elastic waves on polycrystalline mixtures of donors and acceptors (for example, 3,6-di-tert-butylcatechol and 3,6-di-tert-butyl-1,2-benzoquinone with the addition of sulfur and polystyrene) results in the formation of monoradicals and radical pairs. The study of the products by ESR spectroscopy and X-ray analysis shows that the solid powder is dispersed to submicroscopic particles, including those of the mixed composition.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1192–1196, May, 1996.     

Investigation of radical pairs produced upon pulse action of elastic waves on the 3,6-di-tert-butylcatechol-3,6-di-tert-butyl-o-benzoquinone-sulfur system

The pulse action of elastic waves on polycrystalline mixtures of 3,6-di-tert-butylcatechol and 3,6-di-tert-butyl-o-benzoquinone produces radical pairs stable at room temperature, and the addition of polycrystalline sulfur considerably increases their yield. The dependences of formation and decay rates of paramagnetic centers on the composition of the mixture were studied. The threshold character of formation of paramagnetic centers at various powers of elastic wave pulse was established.Translated fromIzvestiya Akademii Nauk. Seriva Khimicheskaya, No. 4, pp. 864–868, April, 1996.     

Molecular complexes in solutions of 2,4,6-tri-tert-butylphenol and 3,6-di-tert-butyl-o-benzoquinones with nonequivalent oxygen atoms

Conclusions In the photolysis of frozen solutions of 2,4,6-tri-tert-butylphenol and 3,6-di-tert-butyl-o-benzoquinones with asymmetric substituents, two types of radical pairs (RP) are formed; this can only be explained by the existence of two types of donor-acceptor complexes in the solutions in the absence of the possibility of hydrogen affinity in the hydroxyphenoxyl radicals,2. In magnetophotoselection experiments, the dependence of the yield of both types of RP on the angle between the electric vector of the exciting plane-polarized light and the direction of the external magnetic field of the spectrometer was observed for all of the systems studied.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 533–537, March, 1986.     

Reaction of stannous bis-3,6-di-tert-butyl-o-semiquinolate with phenoxyl radicals

An EPR study was carried out on the reaction of stannous bis-3,6-di-tert-butyl-o-semiquinolate with several phenoxyl radicals. An oxidative addition reaction may proceed with the formation of radicals with stannic ions. The reaction of biradical stannous complexes with 3,6-di-tert-butyl-2-hydroxyphenoxyl in the presence of triphenylphosphine in toluene gave a tin-containing free radical. The EPR spectra of this radical indicated rapid interligand exchange of the unpaired electron and bond.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1532–1535, July, 1990.     

Study of the structure of free radicals in irradiated monocrystals of N-formyl-L-leucine at room temperature

A study was carried out on the structure of the radical formed upon -radiolysis of monocrystals of N-formyl-L-leucine by ESR spectroscopy and quantum chemical calculations. The calculated ESR parameters for the radical conformations, corresponding to an energy minimum, are in best accord with the experimental values.Tbilisi State University and Institute of Chemical Kinetics and Combustion, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 30, No. 6, pp. 54–58, November–December, 1989.     

Zinc and cadmium complexes based on 3,6-di-tert-butyl-o-benzoquinone

Zinc and cadmium bis-o-semuquinolate and catecholate complexes are synthesized by the reduction of 3,6-di-tert-butyl-o-benzoquinone (3,6-Q) with amalgamated metals in a medium of various solvents. The oxidation of the metal catecholate derivatives results in the corresponding mono-o-semiquinone complexes, which undergo symmetrization to form the metal bis-o-semiquinolates. The molecular structures of the complexes (3,6-SQ)₂Zn · Py, (3,6-SQ)₂Zn · H₂O, and (3,6-SQ)₂Cd · α,α′-Bipy (3,6-SQ is the radical anion of 3,6-Q) are studied by X-ray diffraction analysis. Magnetochemical studies are carried out for the zinc and cadmium bis-o-semiquinone complexes.     

Electron transfer and paramagnetic products of reactions of haloquinones with aliphatic amines

The reactions of chloranil (Cl₄Q) and bromanil (Br₄Q) with aliphatic amines in a DMF : H₂O (5 : 1, vol/vol) mixture were studied. The radical anions of 2,5-didimethylamino-3,6-chloro-p-benzoquinone and 2,5-didimethylamino-3,6-bromo-p-benzoquinone were identified by ESR spectra. The reaction rate constant of the replacement of two chlorine atoms by the amino groups in the radical anion of Cl₄Q at 288 K was estimated.     

双阳离子咔唑衍生物与DNA相互作用的光谱研究

合成了一种新型的双阳离子咔唑衍生物3,6-双(1-羟乙基-4-烯基吡啶)咔唑碘盐(3,6-BHVC), 并对其进行了表征. 利用紫外-可见吸收光谱、圆二色谱、单光子和双光子荧光发射光谱探讨了该化合物与DNA的结合方式. 所有光谱测试结果表明, 该化合物在[磷酸根]/[染料]比值较低的条件下主要以插入方式与DNA结合, 在该比值较高的条件下主要以沟槽结合方式为主. 表明咔唑衍生物可以成为一种探索具有高结合能力双光子DNA探针的基本结构.     

The reaction of 3,6-di-tert-butyl-1,2-benzoquinone and 3,6-di-tert-butylcatechol withtert-butyl hydroperoxide

Reaction of 3,6-di-tert-butyl-1,2-benzoquinone and 3,6-di-tert-butylcatechol withtert-butyl hydroperoxide in aprotic solvents leads to the generation of semiquinone (SQ^.H), alkylperoxy (ROO^.), and alkyloxy radicals. The reaction of SQ^.H and ROO^. produces 2,5-di-tert-butyl-6-hydroxy-1,4-benzoquinone, 3,6-di-tert-butyl-1-oxacyclohepta-3,5-diene-2,7-dione, and 2,5-di-tert-butyl-3,6-dihydroxy-1,4-benzoquinone. The radical generated from solvent attacks SQ^.H at position 4 with C−C bond formation. 4-Benzyl-2,5-di-tert-butyl-6-hydroxycyclohexa-2,5-diene-1-dione produced in this way is transformed into 4-benzyl-3,6-di-tert-butyl-1,2-benzoquinone under the reaction conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 943–946, May, 1999.     

Synthesis of homopolymers and block copolymers of methyl methacrylate and styrene in the presence of bis(3,6-ditert-butylcatecholato)tin(IV) ditetrahydrofuranate

The specific features of synthesis of poly(methyl methacrylate) and polystyrene in the presence of bis(3,6-ditert-butylcatecholato)tin(IV) ditetrahydrofuranate were studied. It was found that the catecholate tin complex can efficiently influence both the kinetic parameters of radical polymerization of the monomers and molecular mass characteristics of the product polymers. With the use on macroinitiators obtained in the presence of bis(3,6-ditert-butylcatecholato)tin(IV) ditetrahydrofuranate, block copolymers were synthesized.     

Homolytic Addition Reaction of Vinylsulfonylfluorobenzene

The reaction of 3,6-bis(vinylsulfonyl)-1,2,4,5-tetrafluorobenzene with a large excess of tetrahydrofuran at 50-55°C gives the homolytic addition product 3,6-bis[2-(2-tetrahydrofuryl)ethylsulfonyl]-1,2,4,5-tetrafluorobenzene. The reaction is effected by peroxides radical process initiators obtained by the autooxidation of tetrahydrofuran.     

High-frequency EPR study of reduced diruthenium and dirhenium polypyridine complexes based on the 1,2,4,5-tetrazine radical bridge

The radical complexes [(micro-L)[Ru(bpy)(2)](2)]*(3+), [(micro-bmtz)[Ru(cym)Cl](2)]*(+) and [(micro-L)[Re(CO)(3)Cl](2)]*(-), where L are 3,6-disubstituted 1,2,4,5-tetrazines such as 3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine (bmtz) and cym =p-cymene, were studied by X-band EPR in fluid solution and by 285 GHz EPR in glassy frozen solution. A comparison with other transition metal complexes (Cu, Rh, Os, Ir, Pt) involving tetrazine radical ligands reveals that the g anisotropy reflects (i) the pi acceptor effect of the tetrazine substituents, (ii) the competition from ancillary pi acceptor ligands for back donation from the metal, and (iii) the spin-orbit coupling contributions from the transition metal.     

Antiradical activity of morpholine- and piperazine-functionalized triphenylantimony(V) catecholates

The antiradical activity of the functionalized triphenylantimony(V) catecholates Ph₃Sb[4-O(CH₂CH₂)₂N-3,6-DBCat] (I), Ph₃Sb[4,5-Piperaz-3,6-DBCat] (II), and Ph₃Sb[4-PhN(CH₂CH₂)₂N-3,6-DBCat] (III) (where [4-O(CH₂CH₂)₂N-3,6-DBCat]^2?, [4,5-Piperaz-3,6-DBCat]^2?, and [4-PhN(CH₂CH₂)₂N-3,6-DBCat]^2? are the dianionic ligands 3,6-di-tert-butyl-4-(morpholin-1-yl)-, 3,6-di-tert-butyl-4,5-(piperazine-1,4-diyl)-, and 3,6-di-tert-butyl-4-(4-phenylpiperazin-1-yl)catecholates, respectively) was studied in reactions with the diphenylpicrylhydrazyl radical during autooxidation of unsaturated fatty (oleic and linoleic) acids with lipid peroxidation of Russian sturgeon (Acipenser gueldenstaedti B.) sperm and human blood erythrocytes in vitro as examples. The EC₅₀ and n _DPPH values obtained indicate the high antiradical activity of complexes II and III in the reactions with the stable radical. On the whole, complexes I–III inhibit the lipid peroxidation in both model (oxidation of unsaturated fatty acids) and in vitro experiments. The inhibiting effects of the complexes are comparable with and even, in some cases, higher than those of the known antioxidant ionol.     

Theoretical and experimental study on the reactivity of methyl dichlorobenzoates with sulfur-centered nucleophiles by electron transfer reactions

Reactions of methyl 2,5-dichlorobenzoate or methyl 3,6-dichloro-2-methoxybenzoate with sulfur-centered nucleophiles gave mono- and disubstitution products, respectively through S_RN1 mechanism in liquid ammonia. Products obtained could be potential herbicides less toxic to the environment. Theoretical studies explained the reactivity observed considering geometries, and spin densities of radical anions and potential energy surfaces for the dissociation of the radical anions formed.     

Antiradical activity of dioxolane derivatives

1,3-Benzodioxoles synthesized by condensation of 3,6-di-tert-butylbenzene-1,2-diol with carbonyl compounds showed antiradical activity due to their ability to undergo one-electron oxidation with formation of stable radical cations. On this basis, the antiknock effect of their structural analogs, 1,3-dioxolanes derived from vicinal diols, was interpreted in terms of oxidation of these compounds with active radicals generated from fuel hydrocarbons to produce more stable radical or radical ion species, depending on the fuel composition. The formation of radical species was detected in model oxidation reactions of 2,2-dimethyl-1,3-dioxolane and 2,2-dimethyl-1,3-dioxolan-4-ylmethanol with radicals generated by photolysis of iron(III) chloride and benzoyl peroxide.     

Mechanism of hindered rotation of the trifluorosilyl group in trifluorosilyl 3,6-di-tert-butylorthosemiquinolate

Conclusions In tetrahydrofurane, ligand permutation in trifluorosilyl 3,6-di-tert-butylorthosemiquinolate is the result of bimolecular synchronous exchange of THF molecules between the radical complex and the solvent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2706–2709, December, 1986.     

Anharmonic thermochemistry of cyclopentadiene derivatives

This paper focuses on the thermochemistry of some derivatives of cyclopenta‐1,3‐diene, namely, 5‐methylcyclopenta‐1,3‐diene, 5‐ethylcyclopenta‐1,3‐diene, 5‐formylcyclopenta‐1,3‐diene, 5‐methylcyclopenta‐1,3‐diene‐1‐yl radical, 5‐ethylcyclopenta‐1,3‐diene‐1‐yl radical, 5‐carbonylcyclopenta‐1,3‐diene radical, 1‐formylcyclopenta‐2,4‐diene‐1‐yl radical, 5‐methylenecyclopenta‐1,3‐diene radical, 5‐ethylidenecyclopenta‐1,3‐diene radical, and 3,6‐dimethylenecyclohexa‐1,4‐diene. Several different chemistries of these compounds are of interest in combustion modeling. Here, we present gas‐phase thermochemical properties for the above cited species, which are, except for 3,6‐dimethylenecyclohexa‐1,4‐diene, previously unknown. These were obtained from corrected (using bond additivity corrections) high‐level ab initio quantum chemistry calculations validated with well‐known compounds including cyclopentane, cyclopentene, cyclopenta‐1,3‐diene, and cyclopentadienyl radical. Heat capacities and entropies have been corrected for anharmonic molecular motions, in particular for internal rotations. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 453–463, 2003