Kinetic parameters of the In(III)/In(I) electrode reaction in bromide medium

The electrode kinetic parameters of the In(III)/In(I) couple in acidic 4M bromide solution have been determined by means of the rotating disc electrode technique.

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Die elektrochemisch-kinetischen Parameter des In(III)/In(I)-Redoxsystems in Bromidlösung (Kurze Mitteilung)

Zusammenfassung Die elektrochemisch-kinetischen Parameter am In(III)/In(I)-Redoxsystem wurden in saurer 4-M-Bromidlösung mittels der rotierenden Scheibenelektrode bestimmt.

     

The reaction of N-Acylpyridinium salts with indole

Depending on the solvent used and the ratio of the reactants, N-acylpyridinium salts condense with indole to give 3-(N-acyl-1,4-dihydro-4-pyridyl)indole ( 1 ) or 4-(N-acyl-3-indolyl)pyridinium chloride ( 3 ). Compound 1 is an intermediate in the formation of compound 3 . The reaction mechanism has been studied, and a hydrogen transfer reaction is suggested as a key step. Alkaline hydrolysis, e.g., of 4-(N-acetyl-3-indolyl)pyridinium chloride ( 3a ), gave 3-(4-pyridyl)indole ( 2a ). The reaction of α-chlorosubstituted acyl halides with indole, in the presence of pyridine constitutes a convenient synthesis of 3-chloroacylindoles.     

C.I. Calculations on the lower transitions in the terphenyl and quaterphenyl di-valent ions

Energies and transition dipole moments for the lower electronic transitions in the terphenyl and quaterphenyl di-valent ions have been calculated starting from the Pople SCF MO's for the ground state ions. The configuration interaction included about one-hundred singly and doubly excited configurations. The results of the calculations for the lower allowed electronic transitions are in very satisfactory agreement with the experimental spectra.     

The clas program for classification and evaluation

Multivariate classification methods are needed to assist in extracting information from analytical data. The most appropriate method for each problem must be chosen. The applicability of a method mainly depends on the distributional characteristics of the data population (normality, correlations between variables, separation of classes, nature of variables) and on the characteristics of the data sample available (numbers of objects, variables and classes, missing values, measurement errors). The CLAS program is designed to combine classification methods with evaluation of their performance, for batch data processing. It incorporates two-group linear discriminant analysis (SLDA), independent class modelling with principal components (SIMCA), kernel density estimation (ALLOC), and principal component class modelling with kernel density estimation (CLASSY). Most of these methods are implemented so as to give probabilistic classifications. Multiple linear regression is provided for, and other methods are scheduled. CLAS evaluates the classification method using the training set data (resubstitution), independent test data, and pseudo test data (leave-one-out method). This last method is optimized for faster computation. Criteria for classification performance and reliability of the given probabilities, etc. are determined. The package contains flexible possibilities for data manipulation, variable transformation and missing data handling.     

Stroboskopisehe Untersuchungen über den zeitlichen Aufbau,die optische Absorption und das Nachleuchten gesteuerter Funkenentladungen

Zusammenfassung In elektrischen Funkenentladungen lassen sich Zündphase, Bogenphase und Abklingphase unterscheiden, die besondere charakteristische Eigenschaften aufweisen. Ihre Untersuchung wird durch ein neu entwickeltes Stroboskop ermöglicht, dessen Phasenlage beliebig gegenüber der periodischen Funkenfolge verstellt werden kann. Durch optische Absorption kann im abklingenden Funken nicht nur der atomare Metalldampf durch seine Grundlinien nachgewiesen werden, sondern auch seine molekularen Reaktionsprodukte mit der umgebenden Atmosphäre lassen sich durch Bandenabsorption feststellen. Das Nachleuchten abklingender Funkenentladungen wird im wesentlichen durch das Nachleuchten des aktiven Stickstoffs getragen, wenn der Metalldampfgehalt der Funkenstrecke gering gehalten wird. Gegen Ende der Nachleuchtphase lassen sich Sprüherscheinungen an den Elektroden feststellen, bei denen kleine Partikelchen mit unterschiedlichen, zum Teil spiralig verlaufenden Bahnkurven ausgeschleudert werden. Die Flugbahnen der Teilchen weisen auf starke Gasströmungen in der Funkenstrecke hin.

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Summary In electrical spark discharges it is possible to distinguish ignition phase, arc phase, and decay phase. These display special characteristic properties. It is possible to study them by means of a newly developed stroboscope, whose phase position can be adjusted at will against the periodic succession of sparks. Through optical absorption, not only the atomic metal vapor can be detected, through its ground lines, in the decaying sparks but also its molecular reaction products with the surrounding atmosphere can be established through the band spectrum. The phosphorescence of decaying spark discharges is essentially due to the afterglow of the active nitrogen, if the metal vapor of the spark gap is kept low. Toward the end of the phosphorescence phase, spray phenomena may be observed at the electrodes, in which tiny particles with distinctive, in part spiral, orbital curves are ejected. The flight paths of these particles indicate strong gas currents in the spark gap.

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Résumé On peut distinguer dans la décharge par étincelles, la phase d'ignition, la phase d'arc et la phase de décroissance. On explique ainsi certaines propriétés caractéristiques. On peut étudier ces diverses phases à l'aide d'un dispositif stroboscopique nouveau réglable à volonté pour observer la même phase d'étincelles qui se succèdent périodiquement. Grâce a l'absorption optique on peut détecter soit une vapeur atomique métallique par ses raies caractéristiques pendant la période de décroissance des étincelles, soit les réactions moléculaires qui se produisent dans les gaz environnants grâce aux spectres de bandes. La phosphorescence pendant la décroissance de l'étincelle est due essentiellement à la postluminescence de l'azote actif, si la tension de vapeur du métal entre les électrodes est suffisamment basse. Pendant la fin de la période de phosphorescence on observe sur les électrodes des phénomènes de pulvérisation avec formation de très petites particules qui sont éjectées en décrivant des trajectoires en spirales. Les trajectoires aériennes de ces particules révèlent l'existence de forts courants gazeux entre les électrodes.

     

Theory of electronic transport in two-dimensional systems in the presence of magnetic fields

Three parts of the paper [Czech. J. Phys.41 (1991) 620,7 are focused on the Landauer-Büttiker approach to the study of transport in two-dimensional electron systems, with particular attention to the influence of an external magnetic field. In the previous parts the Landauer formalism was generalized for two-dimensional systems in quantizing magnetic fields. In the present part we applied the formalism to an analysis of magnetoresistance measurements. The two-dimensional electron gas preserved in the non-dissipative quantum Hall regime acts as the ideal leads necessary in the Landauer-Büttiker approach. The voltage, applied to the gate, forms a scattering region in the gated part of the sample, in between of its undisturbed parts (ideal leads). The dependence of the resistance on the gate voltage and the number of available channels within the ideal leads are discussed.The author wishes to thank to Professor P. Steda for cooperation and to Professor L. Smrka for his encouragement and support. Dr. R. J. Haug should be acknowledged for providing his experimental results.     

Longitudinal acceptance computation for A 50 MeV race track microtron

The algorithm for analysing of longitudinal motion and for calculating phase trajectory in race track microtron (RTM) with small injection energy and small energy gain per turn is described. A longitudinal acceptance is calculated.We are indebted to E. A. Perelshtein and N. Ju. Kazarinov and A. Ju. Molodozhencev for stimulating advices. We thank M. Slodika for work with program coding.     

Derivatives and reactions of glutaconaldehyde—XIII: Regiospecific ring opening of 3-substituted pyridines

A number of nucleophilic ring openings of 3-substituted pyridinium salts have been reinvestigated and summarized. The structure of the resulting stable glutaconaldehyde derivatives was investigated in detail by ¹H NMR. It has been concluded that in general nucleophilic pyridinium ring openings are highly regiospecific. In each case investigated to date a single product was isolated, as a result of attack by the nucleophile at only one of the pyridine α-positions. With the OH ion as the only nucleophile, attack occurs at the pyridine C-2, while larger nucleophiles such as amines and carbanions attack at the pyridine C-6. This was found to be the case for a variety of 3-substituted pyridines such as 3-methyl, 3-methoxy-, 3-cyano-, 3 chloro-pyridine.     

Theory-enforced Re-investigation of the Origin of the Large Metal–Carbon Bond Strength in PdCH2I+ and its reactions with unsaturated hydrocarbons

State-of-the-art ab initio studies demonstrate that the reaction Pd⁺ + CH₃I → PdCH₂I⁺ + H^. is endothermic by ca. 20 kcal/mol, which translates into a bond dissociation energy (BDE) of ca. 83 kcal/mol for the Pd⁺? CH₂I bond. This figure is in agreement with an experimental bracket of 68 kcal/mol < BDE(Pd⁺? CH₂I) < 92 kcal/mol. Based on these findings, the previously studied Pd⁺/CH₃I system was re-investigated, and double-resonance experiments demonstrate that the formation of PdCH₂I⁺ occurs stepwise via PdCH as a reactive intermediate. Further, ion/molecule reactions of PdCH₂I⁺ with unsaturated hydrocarbons are studied, which reveal the formation of carbon–carbon bonds in the gas phase.