Kinetics of cerium(IV) oxidation of macrocyclic complexes of chromium(III) and fate of chromium(IV) intermediates

Kinetics and mechanism of the cerium(IV) oxidation of Cr(III) complexes of a series of macrocyclic (or pseudomacrocyclic) ligands with [14]-membered intraligand ring-sizes have now been investigated at I = 1.0 M (LiClO₄) Temp. 30°C. The complexes of the formulation Cr(macrocycle)(X)(H₂O) where X = CHCl₂ and H₂O, n = 0 or 1 undergo oxidation to Cr(VI) with the formation of chromium(IV) intermediates. The observed kinetic parameters for the Ce(IV) oxidation of Cr(III) macrocyclic complexes have been discussed in terms of changes brought about by the macrocyclic ligands on the Cr(III)—Cr(IV) redox potentials and in specific rates for Cr(IV)—Cr(V) conversion. On the basis of this study, it has been suggested that the trapping of Cr(IV) is easier when a macrocyclic ligand having a symmetrical intra-ligand ring size and unsaturation in the cyclic structure is coordinated equatorially. Cyclic voltammetric studies indicate the formation of Cr(IV) transient in the case of electrochemical oxidation of trans-Cr(Me₄[14]tetraene)(H₂O).     

A generator co-ordinate approach to the breathing mode

In the harmonic approximation of the generator co-ordinate method (GCM) with the Skyrme interaction we show that the frequency of the breathing mode is essentially the same as the semiclassical result. The accuracy of the harmonic approximation is tested in ¹⁶O. Also, a comparison is made between the adiabatic time-dependent Hartree-Fock (ATDHF) theory and an anharmonic version of the GCM.     

Novel pyridine catalysed reactions of dimethyl acetylenedicarboxylate (DMAD) and arylmethylidenemalononitriles: a stereoselective synthesis of highly substituted buta-1,3-dienes

A pyridine catalysed addition of dimethyl acetylenedicarboxylate to various arylmethylidenemalononitriles to afford highly substituted 1,3-butadienes with complete stereoselectivity is described.     

Non perturbative anomalies in higher dimensions

We study how nonperturbative anomalies can occur in dimensions higher than four and their implications on the consistency of the theory.     

Photoelectronic properties of PbI2 using dye-lasers

Summary Pure PbI₂ single crystals have been grown by the zone-refining technique and the spectral distribution of the photocurrent by using different dye-lasers has been recorded withE‖c andE⊥c. The fundamental absorption edge appears at 2.36 eV (E⊥c) and is found to be dichromatic in nature with a splitting of 0.05 eV. The decay pattern of the photocurrent at different voltages, temperatures and intensities of illumination has been used to calculate the lifetimes of charge carriers. The photocurrent-voltage characteristics have been used to calculate the trap concentration and mobility of the charge carriers. The lux-ampère characteristics at the band edge frequency have been studied at different applied voltages.

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Riassunto Monocristalli puri di PbI₂ sono stati accresciuti con la tecnica di raffinazione a zone ed è stata registrata la distribuzione spettrale della fotocorrente con l'uso di diversi laser a colore conE‖c eE⊥c. Il bordo di assorbimento fondamentale appare a 2.36 eV (E⊥c) e appare essere dicromatico in natura con una separazione di 0.05 eV. Lo schema di decadimento della fotocorrente a diversi voltaggi, temperature ed intensità d'illuminazione è stato usato per calcolare le vite medie dei portatori di carica. Le caratteristiche di voltaggio-fotocorrente sono state usate per calcolare la concentrazione di trappole e la mobilità dei portatori di carica. Le caratteristiche lux-ampère alla frequenza del bordo della banda sono state studiate con diversi voltaggi applicati.

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Резюме Выращивается чистый монокристалл PbI₂. Регистрируется спектральное распределение фототока, используя различные лазеры на красителях, в случаеE‖c иE⊥c. Фундаментальный край поглощения возникает при 2.36 эВ (E⊥c). Обнаружена дихроматичность с расщеплением 0.05 эВ. Кривые затухания фототока при различных напряжениях, температурах и интенсивностях облучения используется для вычисления времени жизни носителей заряда. Зависимость фототока от напряжения используется для вычисления концентрации ловушек и подвижности носителей зарядов. При различных приложенных напряжениях исследуются зависимости фототока от интенсивности облучения при частотах, соответствующих краю зоны.

     

A note on the covariant anomaly as an equivariant momentum mapping

We show that there is a natural gauge invariant presymplectic structure on the spaceA of all vector potentials. The covariant axial anomaly is found to be the essentially unique infinitestimally equivariant momentum mapping for the action of the group of gauge transformations on (A,). The infinitesimal equivariance of is shown to be equivalent to the Wess-Zumino consistency condition for the consistent axial anomalyG. We also show that theX operator of Bardeen and Zumino, which relatesG and , corresponds to the one-form (onA) of the presymplectic structure.Research supported in part by NSF grant MCS 81-08814(A03)Research supported by the U.S. Department of Energy under contract number DE AC02 76 ER 02220     

Effect of metal oxide catalysts on thermal decomposition of potassium bromate

Kinetic studies on the effect of metal oxide catalysts, (25% w/w) such as Cr₂O₃, CuO, MnO₂, Al₂O₃ and TiO₂, on the thermal decomposition of KBrO₃ have been carried out. The kinetic parameters of the catalysed and uncatalysed decompositions were calculated by the Freeman-Carroll, Coats-Redfern and Horowitz-Metzger methods. It has been found that Al₂O₃ is almost as good a catalyst as any other oxide used unlike in the thermal decomposition of KClO₃. In the case of TiO₂ there was an increase in the activation energy of decomposition. Of the other oxides Cr₂O₃ underwent reaction and was converted to dichromate and so the parameters of the reaction were not calculated. The effect of varying amounts of Al₂O₃ on the thermal decomposition was also studied.

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Zusammenfassung Kinetische Untersuchungen bezüglich der Wirkung von Metalloxid-katalysatoren z. B. 25 Gew. %, Cr₂O₃, CuO, MnO₂, Al₂O₃ und TiO₂ auf die thermische Hersetzung von KBrO₃ wurden durchgeführt. Die kinetischen Parameter der katalysierten und nichtkatalysierten Zersetzungen wurden mit den Methoden von Freeman-Carroll, Coats-Redfern und Horowitz-Metzger errechnet. Es wurde festgestellt, dass — im Gegensatz zur thermischen Zersetzung von KClO₃-Al₂O₃ ein beinahe so guter Katalysator ist wie jedes andere angewandte Oxyd. Im Falle von TiO₂ trat eine Erhöhung der Aktivierungsenergie der Zersetzung auf. Von den anderen Oxiden trat Cr₂O₃ in Reaktion und wurde zu Dichromat umgesetzt, deswegen wurden diese Reaktionsparameter nicht berechnet. Die Wirkung verschiedener Mengen von Al₂O₃ auf die thermische Zersetzung wurde ebenfalls untersucht.

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Résumé Des études cinétiques sur l'influence d'oxydes métalliques tels que Cr₂O₃, CuO, MnO₂, Al₂O₃ et TiO₂ comme catalyseurs (25 % en poids) de la décomposition thermique de KBrO₃ ont été effectuées. Les paramÊtres cinétiques des réactions de décomposition catalysé es ou non ont été calculés par les méthodes de Freeman-Carroll, Coats-Redfern et Horowitz-Metzger. On a établi que — contrairement à la décomposition thermique de KClO₃-l'oxyde Al₂O₃ était un catalyseur presque aussi bon que n'importe quel autre oxyde utilisé. Dans le cas de TiO₂ l'énergie d'activation de la décomposition se trouve augmentée. Parmi les autres oxydes, Cr₂O₃ entre en réaction et se transforme en bichromate; c'est pourquoi les paramÊtres de la réaction n'ont pas été calculés. L'effet de quantités variables en Al₂O₃ sur la décomposition thermique a également été étudié.

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(25 .%), ₂₃, u, n₂, l₂₃ i_{2 3}. - , - . , l₂₃ , , , ClO₃. iO₂ . ₂₃ , . l₂₃ .

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The authors are thankful to Dr. S. S. Moosath, Professor of Chemistry, University of Calicut, for encouragement and to Dr. K. H. Stern, Naval Research Laboratory, Washington (DC) for graciously providind reprints from High Temperature Properties of Inorganic Salts.     

Formation of highly caged compounds through Diels—Alder cycloaddition of 3-bromo-7-(bromomethyl)tetracyclo[5.3.1.02,6.04,8]undeca-10(12)-ene-9,11-dione with itself and with cyclopentadiene

Diels–Alder reaction of the cage compound2 with itself, leading to the highly caged compound3, as well as with cyclopentadiene, leading to compounds 4 and5, is described.     

A novel approach to the synthesis of bicyclic lactones via an interrupted Nazarov reaction of gem-divinyl dihydrofurans

[reaction: see text] A facile Lewis acid induced interrupted Nazarov reaction of gem-divinyl dihydrofurans to bicyclic lactones is described.