ToBaD: A method for the estimation of torsion barriers from crystal structure data; conformational analysis of N,N-dimethylaniline and derivatives

A new method for the estimation of torsion barriers and its application to conformational analysis is presented. This method, the ToBaD method (method of the torsion barrier derivative), makes use of crystal structure data. It is based on the assumption that the conformation of a compound in the crystalline phase must be very close to a (local) minimum energy conformation of this compound in the gas phase. The ToBaD method is demonstrated for the rotation of the phenyl-N bond in N,N-dimethylaniline. Two geometries of this compound are handled separately: one in which the nitrogen substituents are in a pyramidal or sp³ geometry, and the other in which the nitrogen atom and its substituents are coplanar (the sp² geometry). It is predicted, by means of the ToBaD method, that for both geometries the conformation in which the nitrogen lone pair or p orbital is perpendicular to the aromatic ring is the lowest energy conformation. © 1994 by John Wiley & Sons, Inc.     

Ab initio computed diabatic potential energy surfaces of OH-HCl

The two four-dimensional diabatic potential energy surfaces (DPESs) for OH-HCl are computed that correlate with the twofold degenerate (2)Pi ground state of the free OH radical. About 20 000 points on the surface are obtained by the ab initio coupled-cluster and multi-reference configuration interaction methods. Analytic forms for the diabatic potential energy surfaces are derived as expansions in complete sets of orthogonal functions depending on the three intermolecular angles. The numeric computation of the angular expansion coefficients is discussed. The distance-dependence of the angular coefficients is represented by the reproducing kernel Hilbert space method. It is checked that both diabatic potentials converge for large intermolecular separations to the values computed directly from the electrostatic multipole expansion. The final DPESs are discussed and illustrated by some physically meaningful one- and two-dimensional cuts through them.     

Spezifische Reaktion zum Nachweis von Chrom(III) und Chromat

Zusammenfassung Ein Tüpfelnachweis für Chrom(III) und Chromat wurde angegeben. Nach Reduktion mit metallischem Zink bildet Chrom(II) mit Phenoxazinfarbstoffen in salzsaurem Milieu violett gefärbte Lösungen. Die Reaktion ist für Chrom spezifisch. IhrpD-Wert beträgt 5,3.

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Specific reaction for the detection of chromium(III) and chromate

Summary A spot test detection of chromium(III) and chromate is given. After reduction with metallic zinc, the resulting chromium(II) yields violet solutions with phenoxazine dyestuffs in a hydrochloric acid medium. The reaction is specific for chromium. ItspD is 5.3.

     

Über Reaktionen von Nitrosophenolen, 1. Mitt.: Reaktion von 1-Nitroso-2-naphthol mit Resorcin

Zusammenfassung In der vorliegenden Arbeit wurde die Reaktion von 1-Nitroso-2-napththol mit Resorcin in Eisessig und in Äther studiert. Als Oxydationsmittel wurden Pb₃O₄ bzw. HNO₃ benutzt. Außer dem schon früher erhaltenen Benzo[a]phenoxazon-(9) und einigen seiner Derivate wurde ein bisher noch nicht beschriebenes Benzo[a]phenoxazon-(9)-12-oxid isoliert und identifiziert. Ein Mechanismus seiner Bildung wird vorgeschlagen und seine Konstitution bewiesen.

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The reaction of 1-nitroso-2-naphthol with resorcin in glacial acetic acid and ether was studied. As oxidants nitric acid and lead (IV)-acetate were employed. In addition to already prepared benzo[a]phenoxazon-(9), and some of its derivates one — till this time not described — benzo[a]phenoxazone-(9)-12-oxid was isolated and identified. The reaction mechanism and the constitution of I are verified.

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Determination of thallium by isotopic dilution method using substoichiometric displacement

A new analytical procedure for the determination of thallium in a wide concentration range has been developed. The method of direct isotopic dilution (IDA) using carrier-free²⁰²Tl and the formerly developed procedure of substoichiometric displacement have been used for the determination of thallium content in various types of analyzed samples e.g. minerals, sediments, ion-exchangers, hydrothermal waters, etc. in the concentration range from several percent to 10^?4%, or subsequently down to 0.01 μg/ml in waters. The results obtained are compared with those of emission spectrometry and activation analysis using (γ, n) reaction. A good agreement was found.     

Retention indices as identification tool in pyrolysis-capillary gas chromatography

Pyrolysis-capillary gas chromatography (Py-cGC) represents important method to identify the analytes in the mixture after thermal degradation. This combines high effective analyte separation on-line coupled with thermal degradation process that depends on analyte structure. System of retention indices has been used for identification of the analytes after on-line pyrolysis and chromatographic separation. The pyrolysate composition has been studied during thermal degradation of polymethylmethacrylate (PMMA) at different pyrolysis temperatures and chromatographic column conditions. Homologues series of n-alkanes have been used for calculation of pyrolysate Kováts retention indices (I) and compared with mass spectrometric (MS) data of pyrolysate model mixture. To identify PMMA thermal degradation products the high density polyethylene (HDPE) as additive standard producing triplets of the olefin homologous series during co-pyrolysis has been used. These homologous series enable to calculate programmed temperature retention indices (ITPGC) to identify the analytes present in the pyrolysate. Calculated I values were compared with published I values databases to identify analytes yielded at different pyrolysis temperatures.     

Wärmeeffekte bei Deformation

Zusammenfassung Aus kalorimetrischen Messungen bei stufenweiser Deformation von Weichkautschukproben und gleichzeitiger Kenntnis der mechanischen Arbeit pro Stufe folgt, daß die von der kinetisch-statistischen Theorie vorausgesetzte Bedingung, die Innere Energie hänge nicht von der Dehnung ab, eine Idealisierung darstellt, die man im tatsächlichen Verhalten selbst bei von der Theorie als geeignet angesehenen Fällen selten oder vielleicht überhaupt nicht verifiziert findet.