Non-empirical LCAO-MO-SCF calculations with gaussian type functions on the electrocyclic transformation of cyclopropyl to allyl

Non-empirical molecular quantum chemical calculations have been performed on the electrocyclic transformation of planar and non planar cyclopropyl anions, to allyl anions in the LCAO-MO-SCF framework using gaussian type functions as atomic orbitals. Employing a total of 37 GTF 3 disrotatory and 2 conrotatory modes of transformation have been considered. A total of 34 calculations have been carried out. In the transformation of planar and non planar cyclopropyl anions to allyl anions, both the disrotatory and conrotatory modes possess activations barriers, those for the conrotatory modes being the lower by substantial margins. A detailed analysis of the energy terms involved show that is little theoretical justification for the postulate that the mode of ring opening depends only on the symmetries of the highest occupied orbitals.

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Zusammenfassung Nichtempirische SCF-MO-Rechnungen mit Gaußfunktionen (GF) für den Übergang des planaren und des unplanaren Cyclopropylanions zum Allyanion wurden vorgenommen. Mit einem Basissatz von 37 GF wurden 34 Rechnungen für 3 disrotatorische und 2 conrotatorische Übergänge durchgeführt. Sowohl die disrotatorischen als auch die conrotatorischen Übergänge besitzen Aktivierungsbarrieren, von denen diejenigen für die conrotatorischen Übergänge stets kleiner sind. Die Analyse der Energieterme gibt wenig Anlaß zu der Annahme, daß die Art der Ringöffnung nur von der Symmetrie des obersten besetzten Orbitals abhängt.

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Résumé Des calculs ab-initio en orbitales gaussiennes ont été effetués sur la transformation de cations cyclopropyliques en cations allyliques. Les barrières d'activation sont toujours plus basses pour la mode conrotatoire que pour la mode disrotatoire. Il est peu évident que l'ouverture du cycle dépende que de la Symmetrie de la plus haute orbitale occupée.

     

Relations between subclasses of greedoids

In previous papers many different classes and constructions of greedoids have been defined and studied. This paper documents inclusion relations among all subclasses of greedoids which are known so far. It will be shown that all inclusion relations are proper and that all but one subclasses of interval greedoids are distinct.

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Zusammenfassung In früheren Arbeiten wurden viele verschiedene Klassen und Konstruktionen für Greedoide eingeführt und studiert. In dieser Arbeit werden alle bekannten Inklusionsbeziehungen zwischen Unterklassen von Greedoiden dokumentiert. Es wird gezeigt, daß alle Inklusionsbeziehungen echt und alle Unterklassen mit einer Ausnahme tatsächlich verschieden sind.

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Supported by the joint research project Algorithmic Aspects of Combinatorial Optimization of the Hungarian Academy of Sciences (Magyar Tudományos Akadémia) and the German Research Association (Deutsche Forschungsgemeinschaft, SFB 21). Part of this research was done while the first author was visiting the Department of Combinatorics and Optimization, University of Waterloo.     

Lösungsmitteleinfluß auf das Redoxverhalten von Bistriphenylphosphinquecksilber(II)-perchlorat

The influence of solvents on the redox behaviour of bistriphenylphosphinomercury perchlorate has been investigated by polarographic, voltammetric and potentiometric methods. The electrode process was found to be reversible in acetonitrile, propylene carbonate, N,N-dimethylformamide and dimethyl sulfoxide. An irreversible process was observed in nitromethane employing the dropping mercury electrode as well as in N,N-dimethylthioformamide and N-methyl-2-thiopyrrolidinone employing the rotating platinum electrode. Half wave potentials and diffusion coefficients have been measured. A linear relationship between theE _1/2 and the donor number (DN) of the solvent has been found for the reversible electrode reactions. Ligand replacement occurs in N,N-dimethylthioformamide and N-methyl-2-thiopyrrolidinone.

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Mit 1 Abbildung     

The application of C-N.M.R. spectroscopy to the determination of the stereochemistry of Diels-Alder adducts

Long-range (³J) ¹³C-H coupling is a reliable probe to evaluate the stereochemistry of cycloaddition products. The method is best applied to carbonyl containing adducts but not restricted to them. Several structures have been revised and new ones evaluated.     

Über einige neue Bispirane

We have obtained four new bispirane systems in which both spiroatoms are vicinal atoms in cyclopropane or cyclobutane rings and in which the heterocyclic component has the basic structure of 1,4-dioxep-2-ene. We have shown that from two possibilities (bispiran, propellan) the general reaction leads only to a bispiran system. To the bispiran2 exhibiting the highest hyperchromism we ascribed the bispirocoplanar conformation (Fig. 1).

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Mit 3 Abbildungen     

A modification of the heteropoly blue method for the microgram determination of arsenic in biological materials

Summary A sensitive method has been developed for analysis of trace amounts of arsenic in biological materials using the heteropoly blue method. The method employs a closed apparatus and a nitrogen atmosphere, and allows the detection of arsenic in ppm concentration using samples of 100 mg.

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Zusammenfassung Eine empfindliche Methode zur Bestimmung von Arsenspuren in biologischem Material im Wege der Molybdänblaumethode wurde ausgearbeitet. Man arbeitet dabei in einer geschlossenen Apparatur in Stickstoffatmosphäre und kann so in 100-mg-Proben Arsenkonzentrationen in der Größenordnung von ppm bestimmen.

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Presented at the 6th Annual Northeast Regional Meeting of the American Chemical Society, Burlington, Vermont, August 19, 1974.     

The polymerization of 1,4-pentadiene to [3.3.1]bicyclo-linked chains

1, 4-Pentadiene has been polymerized by Ziegler-Natta catalysts to give amorphous polymers which are up to 64 wt.-% soluble. The polymers all have residual unsaturation which is substantially less than one double bond per mer, some as low as 0.1 double bond per mer. The polymerizations proceed by an unusual double inter-, double intramolecular cyclopolymerization mechanism leading to the formation of [3.3.1] bicyclic repeat units. Some main-chain (internal) unsaturation as well as pendant-group (external) unsaturation is observed. The latter results from incompletely cyclized 1,4-pentadiene units. The former is due to some concurrent isomerization of 1,4- to 1,3 pentadiene, which then copolymerizes with the 1,4 diene. The extent of isomerization varied with the catalyst system used. The soluble polymer fractions were brittle for internal unsaturations of less than about 0.05 double bond per mer and were viscous for higher values. The insoluble fractions were brittle and are believed to be lightly crosslinked.