On the role of symmetric hydrogen bonds of increased strength in isotope exchange of dihydrogen with water-alkaline solutions

The chemical effect of a hydrogen bond of increased strength responsible for the existence of H₃O ₂ ^– and determining mainly the E_a of the catalytic isotope exchange (IE) of hydrogen with water-alkaline solutions (WAS) is discussed. Assuming that the H₃O ₂ ^– associates are also effective in the case of water-alkaline melts (WAM), experimental kinetic evidence in favor of the suggested treatment of the IE mechanism is considered.

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, H₃O ₂ ^– E_a () (). H₃O ₂ ^– - () .

     

Influence of anchored cerium ions on the dispersity and activity of Pd/SiO2 catalysts

(Pd+Ce)/SiO₂ catalysts prepared by decomposition of organometallic complexes of Ce and Pd have higher activity, dispersity and selectivity in methanol synthesis than Pd/SiO₂ catalysts.

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, (Pd+Ce)/SiO₂ , Ce Pd, Pd/SiO₂.

     

Influence of hydrogen on the aromatization of ethane over Pt/H-ZSM-5 zeolite

Hydrogen influences the activity and selectivity of a Pt/H-ZSM-5 zeolite in ethane aromatization by favoring hydrogenolysis and suppressing dehydrogenation and coking. H₂ formed during the reaction inhibits the aromatization activity.

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Pt/H-ZSM-5 , . H₂, , .

     

Kinetics of reduction of tungstovanadophosphoric heteropoly anions with VO2+ ions

The rate constants of interactions of PW_12-nV_nO₄₀ ^(3+n)– (n=1–4) heteropoly anions (HPAs) and various PW₁₀V₂O₄₀ ^–5 isomers with VO²⁺ were measured. The reactions occurred via formation of intermediate active complexes with V(IV) ions incorporated into the coordination sphere of HPA.

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VO²⁺ PW_12-nV_nO₄₀ ^–(3+n) (n=1–4) PW₁₀V₂O₄₀ ^–5. , V(IV) .

     

Reaction of triphenyl phosphite ozonide with thioacetals

Kinetic regularities in the reaction of triphenyl phosphite ozonide with several thioacetals in CH₂Cl₂ solution at –15°C have been studied. The consumption rate of ozonides is described by the kinetic equation W=k₀[(C₆H₅O)₃P·O₃]+k₁[(C₆H₅O)₃P·O₃][R₁R₂C(SR₃)₂] Rate constants k₀ and k₁ for the thioacetals: (CH₃H₇S)₂CH₂, (C₆H₅S)₂CH₂, (C₆H₅CH₂S)₂CH, (n=C₁₂H₂₅–S)₂CH₂, (C₃H₇S)₂C(H)CH₃, (C₃H₇S)₂C(H)C₆H₅, (C₃H₇S)₂C(CH₃)C₆H₅ and (C₃H₇S)₂C(H)C₁₀H₉, increases with increasing the electron-donating power of subtituents R_i.

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CH₂Cl₂ –15°C. : W=k₀[(C₆H₅O)₃P·O₃]+k₁[(C₆H₅O)₃P·O₃][R₁R₂C(SR₃)₂] k₀ k₁ (C₃H₇S)₂CH₂, (C₆H₅S)₂CH₂, (C₆H₅CH₂S)₂CH₂, (n-C₁₂H₂₅S)₂CH₂, (C₃H₇S)₂C(H)CH₃, (C₃H₇S)₂C(H)C₆H₅, (C₃H₇S)₂C(CH₃)C₆H₅, (C₃H₇S)₂C(H)C₁₀H₉. .

     

Physical properties of the catalyst used for the partial oxidation of anthracene to anthraquinone. I. M?ssbauer study

Mössbauer measurements on the intermediate and active material used for partial oxidation of anthracene to anthraquinone are reported. The fraction of ferric and ferrous ions as well as their coordination types are determined.

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, . , .

     

Polymeric membrane sodium-selective electrodes based on calix[4]arene ionophores

Six kinds of tetra alkylester type calix[4]arene derivatives, (R₁=R₂=CH₃1, C₂H₅2, C₃H₇3,n-C₄H₉4,t-C₄H₉5,n-C₁₀H₂₁6), a diethyl-didecyl mixed ester type (R₁=C₂H₅, R₂ =C₁₀H₂₁7), and three kinds of lower rim bridged types (R₁=C₂H₅, R₂–R₂=(CH₂)₁₀8, (CH₂)₁₂9, (CH₂)₂(OCH₂CH₂)₃10) were characterized by electrochemical measurement to elucidate the effect of the length of the alkyl group of alkoxycarbonyl substituents on Na⁺ selectivity. To obtain excellent Na⁺ selective ionophores, introduction of short chain alkyl groups rather than long chain ones, such as a decyl group, and maintenance of sufficient solubility of the calix[4]arene derivatives in the membrane solvent are required concurrently. Among the calix[4]arenes tested, 25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]-p-tert-butylcalix[4]arene2, and the diethyl-didecyl mixed ester type derivative7 are the best ionophores for a Na⁺ selective electrode. On the other hand, sodium selectivity of the bridged type derivative9 is comparable or even superior to that of the known bis(12-crown-4).This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

Synthesis of some 5′-O-amino acid derivatives of uridine as potential inhibitors ofUDP-glucuronosyltransferase

Summary In an attempt to develop potential inhibitors ofUDP-glucuronosyltransferase, some 5-O-amino acid derivatives of uridine were synthesized. N-protectedL-amino acids were coupled at the 5-O-position of 2,3-O-isopropylideneuridine by esterification employing the method of symmetrical anhydrides in presence of 4-dimethylaminopyridine, 5-O-(N-benzyloxycarbonyl-O-tert.butyl-L-threonl)-23-O-isopropylideneuridine (1), 5-O-(N-tert.butyloxycarbonyl-O-benzyl-L-seryl)-2,3-O-isopropylideneuridine and (2), 5-O-(N-tert.butyloxycarbonyl-L-valyl)-2,3-O-isopropylideneuridine (3), and 5-O-(N-tert.butyloxycarbonyl-L-valyl)-2,3-O-isopropylideneuridine (4) were obtained in good yield after column chromatography on silica gel. The treatment of2 withTFA/CH₂Cl₂ (6:1) at room temperature for 30 min led to a selective removal of theBoc group without deblocking of the 2,3-O-isopropylidene group of uridine. Treatment of2 withTFA/H₂O (5:1) at room temperature for 1 h, however, released bothBoc and 2,3-isopropylidene groups. TheZ group of1 was deprotected by catalytic hydrogenolysis over 10% Pd/C/ammonium formate.

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Synthese von 5-O-Aminosäurederivaten des Uridins als potentielle Inhibitoren derUDP-Glukuronosyl-Transferase

Zusammenfassung In einem Versuch, potentielle Inhibitoren derUDP-Glukuronosyl-Transferase zu entwickeln, wurden einige 5-O-Aminosäurederivate des Uridins synthetisiert. N-GeschützteL-Aminosäuren wurden durch Veresterung mit der 5-O-Position des 2,3-isopropylidenuridins gekuppelt (Methode der symmetrischen Anhydride in der Gegenwart von 5-Dimethylaminopyridin). Solcherweise wurden 5-O-(N-Benzyloxycarbonyl-O-tert.butyl-L-threonly)-2,3-O-isopropylidenuridin (1), 5-O-(N-tert.Butyloxycarbonyl-O-benzyl-L-seryl)-2,3-O-isopropylidenuridin (2), 5-O-(N-tert.Butyloxycarbonyl-L-leucyl)-2,3-O-isopropylidenuridin (3) und 5-O-(N-tert.Butyloxycarbonyl-L-valyl)-2,3-O-isopropylidenuridine (4) nach Säulenchromatographie (Kieselgel) in guter Ausbeute hergestellt. Die Behandlung von2 mitTFA/CH₂Cl₂ (6:1) bei Zimmertemperatur (30 min) führte zu einer selektiven Abspaltung derBoc-Gruppe ohne Deblockierung der 2,3-O-Isopropylidengruppe des Uridins. Eine Behandlung von2 mitTFA/H₂O (5:1) bei Zimmertemperatur für 1 Stunde führte hingegen zur Abspaltung sowohl derBoc als auch der 2,3-O-Isopropylidengruppe. DieZ-Gruppe von1 wurde durch katalytische Hydrogenolyse auf 10% Pd/C/Ammoniumformiat abgespalten.

     

Silica-immobilized binuclear chromium-molybdenum complexes

ESR and UV spectra of a binuclear complex [n-(C₄H₉)₄N]₃ CrMoOCl₉ in solution and supported on SiO₂ have been studied. Upon fixing this complex followed by oxidation-reduction treatment, a highly disperse state is observed, as evidenced by the ESR spectra of the Cr³⁺ ions.

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[H–(C₄H₉)₄N]₃CrMoOCl₉ SiO₂. - , Cr³⁺.

     

Nitrate and sulfite catalyzed reaction of monooxalatotetraaquachromium(III) and ethylenediaminetetraacetate

The kinetics of the reaction between monooxalatotetraaquachromium(III) and ethylenediamenetetraacetate have been studied in acidic media. The reaction is accelarated by nitrite and sulfite ions. The mechanism for the catalyzed reaction is discussed in terms of the formation of Cr(ONO)(ox)(H₂O)₃ and Cr(OSO₂H)(ox)(H₂O)₃. The catalytic effect of sulfite is greater than that of nitrite. Spectral evidence is presented for the formation of nitrito and sulfito species.

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() (III) . , . Cr(ONO)(ox)(H₂O)₃ Cr(OSO₂H)(ox)(H₂O)₃. . .

     

Thermal and calorimetric investigations on crystalline hydrates of barium hydroxide and their deuterated analogues

The thermal decompositions of Ba(OH)₂ · 8H₂O, Ba(OH)₂ · 8D₂O, Ba(OH)₂ · H₂O and Ba(OH)₂ · D₂O were studied and the phase transitions were identified by DSC and DTA methods. The corresponding enthalpy changes were determined and compared with those calculated from the thermodynamic data. A decrease of the thermal stability was demonstrated for the deuterated crystal hydrates in comparison with the normal ones.

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Zusammenfassung Die thermische Zersetzung von Ba(OH)₂ · 8H₂O, Ba(OH)₂ · 8D₂O, Ba(OH)₂ · H₂O und Ba(OH)₂ · D₂O wurde untersucht. Phasenübergänge wurden mittels DSC und DTA ermittelt. Die entsprechenden Enthalpieveränderungen wurden bestimmt und mit den aus thermodynamischen Daten berechneten Werten verglichen. Die deuterierten Kristallhydrate sind thermisch weniger stabil als die leichtes Kristallwasser enthaltenden Verbindungen.

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()₂ · 8₂, ()₂ · 8D₂O, Ba(OH)₂·H₂O Ba(OH)₂·D₂O. , . .

     

The oxidative addition of diphenylphosphine and monophenylphosphine to the electron-rich rhenium-rhenium triple bond. The isolation and characterization of compounds that contain the four-center Re(μ-X)(μ-PR2)Re cluster (X=halide)

Diphenylphosphine oxidatively adds to the ReRe bonds of Re₂ X ₄(-dppm)₂ (X=Cl or Br; dppm=Ph₂PCH₂PPh₂) and Re₂Cl₄(-dpam)₂ (dpam=Ph₂AsCH₂AsPh₂) to afford the dirhenium(III) complexes Re₂(-X)(-PPh₂)HX ₃(-LL)₂. The dppm complexes have also been prepared from the reactions of Re₂(-O₂CCH₃)X ₄(-dppm)₂ with Ph₂PH, and a similar strategy has been used to prepare Re₂(-Cl)(-PPh₂)HCl₃(-dmpm)₂ (dmpm=Me₂PCH₂PMe₂) from Re₂(-O₂CCH₃)Cl₄(dmpm)₂. Phenylphosphine likewise reacts with Re₂ X ₄(-dppm)₂ to give Re₂(-X)(-PHPh)HX ₃(-dppm)₂. An X-ray crystal structure determination on Re₂(-Cl)(-PPh₂)HCl₃(-dppm)₂ confirms its edge-shared bioctahedral structure. This complex crystallizes in the space group (No. 148) witha=21.699(3) Å, =84.50(4)°,V=10084(5) ų, andZ=6. The structure was refined toR=0.049 (R _w 0.069) for 5770 data withI>3.0(I). The Re-Re distance is 2.5918(7) Å. Oxidation of the bromide complex Re₂(-Br)(-PPh₂)HBr₃(-dppm)₂ with NOPF₆ produces the unusual dirhenium(III, II) cation [Re₂(-H)(-Br)[P(O)Ph₂]Br₂(NO)(-dppm)₂]⁺ which has been structurally characterized as its perrhenate salt, [Re₂(-H)(-Br)[P(O)Ph₂]Br₂(NO)(-dppm)₂]ReO₄ · 2CH₂Cl₂. This complex crystallizes in the space group (No. 2) witha=14.187(7) Å,b=16.419(5) Å,c=16.729(5) Å, =98.76(2)°, =110.11(3)°, =104.66(3)°,V=3414(6) ų,Z=2. The structure was refined toR=0.040 (R _w =0.051) for 5736 data withI>3.0(I). The presence of a phosphorus-bound [P(O)Ph₂]^– ligand, a linear nitrosyl and a bridging hydrido ligand has been confirmed. The Re-Re distance is 2.6273(8) Å.     

IR and thermal studies on lithium oxomolybdenum(VI) oxalate

A new molybdenum(VI) complex, Li₂[Mo₂O₆(C₂O₄)] · 2 H₂O (LMO), was prepared and characterized by chemical analysis and IR spectral studies. Its thermal decomposition was studied by using TG and DTA techniques. LMO loses its two moles of water between 75 and 170° to give the anhydrous product, which decomposes in three stages between 240 and 380°. The first two stages occur in the temperature ranges 240–280° and 280–305°, to give intermediates with the tentative compositions Li₆[Mo₆O₁₉(C₂O₄)₂] and Li₆[Mo₆O₂₀(C₂O₄)], respectively. In the third stage, which extends up to 380°, Li₆[Mo₆O₂₀(C₂O₄)] decomposes to give the end-product, Li₂Mo₂O₇.

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Zusammenfassung Ein neuer Molybdän(VI)-Komplex der Formel Li₂[Mo₂O₆(C₂O₄)] · 2 H₂O (LMO) wurde dargestellt und durch chemische Analyse und IR-spektroskopisch charakterisiert. Die thermische Zersetzung dieses Komplexes wurde mittels TG und DTA untersucht. LMO verliert die zwei Wassermoleküle zwischen 75 und 170° unter Bildung des wasserfreien Produktes, das zwischen 240 und 380° in drei Stufen zersetzt wird. Die in den Temperaturbereich von 240–280° und 280–305° verlaufenden ersten zwei Reaktionsschritte ergeben Intermediäre der tentativen Zusammensetzung Li₆[Mo₆O₁₉(C₂O₄)₂] bzw. Li₆[Mo₆O₂₀(C₂O₄)]. In dem sich bis 380° erstreckenden dritten Reaktionsschritt wird Li₆[Mo₆O₂₀(C₂O₄)] unter Bildung des Endproduktes Li₂Mo₂O₇ zersetzt.

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Li₂[MO₂O₆(C₂O₄] · 2 ₂ . . - 70–170° , , 240–380°. 240–280° 280–305° - Li₆[Mo₆O₁₉(C₂O₄)₂] Li₆[Mo₆O₂₀(C₂O₄)]. - 380° Li₂Mo₂O₇.

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The authors are grateful to Prof. S. N. Tandon, Head of the Chemistry Department, for providing the research facilities.     

Investigations of thermal elimination reactions of polymers by thermal volatilization analysis and ultraviolet spectroscopy

Using thermal volatilization analysis with differential condensation of volatile products, with film samples on flat-bottomed silica glass reaction tubes to permit measurements of UV spectra of partly degraded polymer, the thermal stability, the types of volatile products and the development of conjugation in the involatile residue have been compared for poly(vinyl chloride), polychloroprene, poly(vinyl acetate) and vinyl acetate/ethylene copolymers, poly(vinyl formate) and poly(vinyl alcohol). All undergo a side-group elimination reaction at lower temperatures, and polyene breakdown occurs in all the samples between 400 and 500°. The longest polyene sequences are formed by PVC. All the polymers except PVC show some complexity of products in the elimination reaction.

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Zusammenfassung Die Anwendung der thermischen Verdampfungsanalyse durch Differentialkondensation der flüchtigen Produkte an Filmproben in flachen Quarzglasreaktionsrohren gestattet die Ermittlung der UV-Spektren von teilweise degradierten Polymeren sowie Aussagen über die thermische Stabilität und Types des flüchtigen Produktes. Die Bindungen in dem nichtflüchtigen Rest wurden untersucht und im Falle der Copolymere Poly(vinylchlorid), Polychloropren, Poly(vinylacetat) und Vinylacetat/Äthylen, weiterhin Poly/vinylformat und Poly/vinylalkohol verglichen. Alle erleiden eine Eliminierungsreaktion an der Seitengruppe bei niedrigeren Temperaturen und Polyenabspaltung zwischen 400 und 500°. Die längsten Polyensequenzen werden durch PVC gebildet. Abgesehen vom PVC zeigten alle übrigen Polymere eine gewisse Komplexität in der Eliminierungsreaktion.

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Résumé L'emploi de la méthode d'analyse par volatilisation thermique avec condensation différentielle des produits volatils, sur des échantillons en film sur tubes de réaction en verresilice à fond plat permet l'examen des spectres ultraviolets des polymères partiellement dégradés et l'étude de la stabilité thermique, outre l'identification des constituants volatils. On a comparé le développement de la conjugaison dans le résidu non-volatil pour les polychlorure de vinyle, polychloroprène, polyacétate de vinyle et les copolymères acétate de vinyle/éthylène, polyformiate de vinyle et polyalcool vinylique. Dans chaque cas, on a observé une réaction d'élimination du groupe latéral à basse température et rupture du polyène entre 400 et 500°. Les plus longues séquences ont été formées dans le cas du PCV. Tous les polymères, excepté le PCV, montrent une certaine complexité de produits dans la réaction d'élimination.

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. (), , , , . , , — - , — . ; 400–500°. . , , .

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Some parts presented at the International Symposium on Macromolecular Chemistry, Budapest, 1969.

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One of the authors (D.L.G.) thanks the Science Research Council for the award of a studentship. Some of the experiments with PVF were carried out by Mr. A. Jamieson. Differential condensation TVA curves were obtained by Mr. R. G. Perrett.     

Acetylene adsorption on a clean iridium surface

The interaction of C₂H₂ with a polycrystalline iridium surface at 140 KT500 K has been studied by AES, XPS and UPS. A model of the bonding between C₂H₂ and Ir by the 1 orbitals of the hydrocarbon is proposed. The more pronounced energy splitting between the orbitals of acetylene during adsorption compared to that in the gas phase is ascribed to deformation of the acetylene molecule.

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C₂H₂ . 140 KT500 K AES, XPS UPS. C₂H₂ Ir 1- . - , , .

     

Determination of the surface acidity of solid catalysts

A novel method has been developed for determining the surface acidity of white, as well as deeply colored porous solids. The method, which was tested on Al₂O₃, SiO₂–MgO–Al₂O₃ and Fe₂O₃ catalysts, is based on the adsorption of pyridine or benzylamine on acidic sites and subsequent displacement of the adsorbed bases by n-butylamine. A linear correlation was found between the concentration of acidic sites on Al₂O₃ and Fe₂O₃ catalysts and their activity in the dehydration oftert-butyl alcohol.

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, . , Al₂O₃, SiO₂–MgO–Al₂O₃ Fe₂O₃, -. Al₂O₃ Fe₂O₃ - .

     

Thermal properties of thiocyanatocopperc(II) complexes with picolines and lutidines

The thermal properties of coordination compounds of the composition Cu(NCS)₂L₂ (whereL=pyridine, 2-, 3- and 4-picoline, and 2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-lutidine) are dealt with. The thermal decomposition of these compounds begins with the release of the ligandL. The compounds with pyridine derivatives containing a methyl substituent at position 2 show a markedly decreased initial decomposition temperature. It was found that X-ray irradiation caused a reduction of the central atom Cu(II) in the coordination compounds under investigation. X-ray electron spectra data showed the stability of the compounds Cu(NCS)₂L₂ withL=picoline or lutidine having a methyl substituent at position 2 to be distinctly lower in the surface layers. From the given series, the compounds Cu(NCS)₂(pyridine)₂ and Cu(NCS)₂(3,5-lutidine)₂ exhibit an analogous course of thermal decomposition in nitrogen atmosphere up to 600°. The stoichiometries of thermal decomposition are discussed.

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Zusammenfassung Der Artikel befaßt sich mit den thermischen Eigenschaften von Koordi-nationsverbindungen der Zusammensetzung Cu(NCS)₂ L ₂ (L= Pyridin, 2-, 3-, 4-Pikolin, 2,3-, 2.4-, 2,5-, 2,6-, 3,4- und 3,5-Lutidin). Die thermische Zersetzung dieser Verbindungen beginnt mit der Abspaltung des LigandenL. Die Verbindungen mit Pyridinderivaten, welche einen Methylsubstituenten in Position 2 im Pyridinring enthalten, zeigen eine deutlich herabgesetzte anfängliche Zersetzungstemperatur. Es wurde gefunden, daß die Röntgenbestrahlung eine Reduktion des zentralen Cu(II)-Atoms bei den untersuchten Koordinationsverbindungen herbeiführte. Die Daten der Röntgen-Elektronenspektren zeigten, daß die Stabilität der Verbindungen Cu(NCS)₂L₂ mitL=Pikolin oder Lutidin, welche einen Methylsubstituenten in Position 2 enthalten, in den Oberflächenschichten wesentlich geringer ist. Von der gegebenen Reihe der Verbindungen zeigen Cu(NCS)₂(Pyridin)₂ und Cu(NCS)₂(3,5-Lutidin)₂ in Stickstoff-Atmosphäre bis zu 600° einen ähnlichen Verlauf der thermischen Zersetzung. Die Stöchiometrie ihrer thermischen Zersetzung wird beschrieben.

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Résumé L'article a trait aux propriétés thermiques des composés de coordination de composition Cu(SCN)₂L₂ (L=pyridine, 2-, 3-, 4-picoline, 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-lutidine). La décomposition thermique de ces composés commence avec la libération du ligandL. Les composés avec des dérivés de la pyridine contenant un substituant méthyle en position 2 sur le cycle de la pyridine présentent une température initiale de décomposition qui se trouve abaissée de manière appréciable. On observe que le traitement aux rayons X provoque une réduction de l'atome central Cu(II) dans les composés de coordination étudiés. Les données fournies par les spectres électroniques des rayons X ont montré que la stabilité des composés Cu(SCN)₂L₂ avecL= picoline ou lutidine, ayant un substituant méthyle en position 2, est nettement plus faible dans les couches superficielles. Dans cette série de composés, Cu(SCN)₂ (pyridine)₂ et Cu(SCN)₂(3,5-lutidine)₂ montrent, en atmosphère d'azote, jusqu'à 600°, un processus analogue de décomposition thermique. La stoechiométrie de leur réaction de décomposition thermique est examinée.

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Cu(NCS)₂L₂ L=, 2-, 3-, 4- , 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-. L. 2- . , , Cu(II). , Cu(NCS)₂L₂ c L= , 2, . Cu(NCS)₂ ( )₂ Cu(NCS)₂ (3,5-)₂ 600°. .

     

Thermal decomposition of calcium sulphate in carbon monoxide

Simultaneous TG and DTA studies were performed on analytical grade calcium sulfate and on samples of natural gypsum and phosphogypsum in carbon monoxide atmosphere. The decomposition temperatures and mechanism are influenced by the mineral impurities of the sample and the heating rate as well as the CO content of the gas atmosphere.

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Zusammenfassung Simultane TG- und DTA-Untersuchungen von analytisch reinem Calciumsulfat und Proben von natürlichem Gips und Phosphogips wurden in Kohlenmonoxidatmosphäre ausgeführt. Temperatur und Mechanismus der Zersetzung werden durch mineralische Verunreinigungen der Probe, durch die Aufheizgeschwindigkeit und durch den CO-Gehalt der Gasatmosphäre beeinflußt.

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. - , , .

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The authors are indebted to Professor M. Veiderma for fruitful discussions and continuous support. The scholarship from Finnish Government to one of us (R. K.) is gratefully acknowledged.     

Influence of o-benzoquinone nature on initiation of radical polymerization by the o-benzoquinone—tert-amine system

o-Benzoquinones initiate radical polymerization of methacrylates under visible light irradiation in the presence of tertiary amines. Spectral sensitivity of the initiating system coincides with absorption bands of o-benzoquinone attributed to the S(*) (_max 400 nm) and S(n*) (_max 600 nm) transitions. The amine radicals (Am^·) initiating polymerization are generated by the photoreduction of Q in the presence of AmH from the triplet radical pair ³(QH^·, Am^·). The yield of Am^· depends on the difference between the volumes of substituents in the 3 and 6 positions of the quinoid ring and is maximal for symmetrically substituted o-benzoquinones. For a series of derivatives of symmetrical 3,6-di-tert-butyl-o-benzoquinone, the rate of photopolymerization of ,-bis(methacryloyloxyethyleneoxycarbonyloxy)ethyleneoxyethylene (OCM-2) in the presence of N,N-dimethylaniline is determined by the free energy (G _e) of electron transfer from the amine to photoexcited o-benzoquinone. The G _e value includes the energies of oxidation of the amines and reduction of the o-quinones and the energy of the 00 transition of the triplet excited state of o-benzoquinones, which are equal to their redox potentials. The photopolymerization rate is maximal for G _e 0.