Sensitivity- and Gradient-Enhanced Heteronuclear Coupled/Decoupled HSQC–TOCSY Experiments for Measuring Long-Range Heteronuclear Coupling Constants

A pulsed field gradient version of the sensitivity-enhanced 2D HSQC–TOCSY experiment is proposed for measurement of long-range heteronuclear coupling constants. The coupling constants are obtained by computer-aided analysis of mixed-phase multiplets with and without the heteronuclear splitting. Generation of pure phase data is not required. Since large¹J_XHandJ_HHcouplings are used for coherence transfer, smallⁿJ_XHcan be measured accurately, which could be difficult to obtain from purely heteronuclear polarization transfer experiments.     

Pseudorandom sequences constructed by the power generator

Summary We study the pseudorandom properties of the power generator (which includes as special cases the RSA generator and the Blum--Blum--Shub generator). In order to estimate the pseudorandom measures character sums with exponential functions are used.     

TLC of steroids VII. Comparative TLC properties of hydroxy-estrones,hydroxy-estradiols and their synthetic intermediates

Thin-layer Chromatographic behavior of 22 steroids were compared in five systems of different compositions and polarities. Some of the steroids studied are new: mainly aromatic steroid derivatives substituted with hydroxy on carbon-2 or carbon-4, or both carbon-2 and carbon-4 of the aromatic ring: from a biological point of view they are of importance as metabolic intermediates.     

Conformation changes induced in 2-spiro-substituted cephalosporin sulphoxides by the configuration of the spiro bond: A combined 1H and 13C NMR study

1,3-Dipolar cycloadditions of diazomethane and diphenyldiazomethane to exo-2-methylenecephalosporins are described. A structural study of the products shows that the initially formed 2-spiropyrazolinocephems form cyclopropanes by the spontaneous loss of nitrogen. ASIS and NOE measurements reveal that the products with different C-2 configurations are in two different conformations.     

Monofunctional (Dimethylamino)silane as Silylating Agent

The reaction of triorganyl(dimethylamino)silanes with surface-hydrated silicon dioxide has been studied. These silylating agents are easy to prepare from the corresponding chloro or bromosilanes with dimethylamine. The resulting products are thermally stable and relatively volatile. Reaction with surface-hydrated silicon-dioxide preparations at 150–250°C for 170 h yields a dense grafted layer. However, with (dimethylamino)silanes having strongly polar substituents, a retreatment of the surface-modified silica seems to be necessary in order to attain maximum coverage.     

Nachweis und volumetrische Bestimmung von Nitrosoderivaten im Mikromaßstab

Zusammenfassung Nitrosoverbindungen lassen sich in Gegenwart von Rhodanidionen durch Eisen(II)-sulfat quantitativ reduzieren. Auf dieser Reaktion beruht ein neuer Nachweis der Nitrosogruppe auf Grund der Farbe des Eisen(III)-rhodanidkomplexes, sowie ihre Bestimmung durch Titration des Eisen(III) mit Quecksilber(I)-nitrat-Maßlösung. Diese Methode ermöglicht die Analyse auch in Gegenwart von Nitroverbindungen.

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Detection and volumetric microdetermination of nitroso compounds

Summary Nitroso compounds can be quantitatively reduced by iron(II) sulphate in the presence of thiocyanate ions. The reaction provides a new method for the detection of the nitroso group, based on the colour developed by the iron(III) thiocyanate complex. The determination of nitroso group can also be carried out by titrating the iron(III) with mercury(I) nitrate, even if nitro compounds are present.

     

The two largest distances in finite planar sets

We determine all homogenous linear inequalities satisfied by the numbers of occurrences of the two largest distances among n points in the plane.     

First-principles investigation of the vibrational properties of 3-tert-butylcyclohexene

I present a first-principles investigation of the vibrational properties of the chiral molecule 3-tert-butylcyclohexene. The vibrational density of states (vDOS) of the two existing conformers has been calculated ab initio within the framework of density-functional theory and density-functional perturbation theory, using both the local-density approximation and the generalized-gradient approximation for the exchange-correlation potential. The vDOS of the two conformers are very similar. The vDOS has been investigated with respect to contributions of the cyclohexene ring and the tert-butyl group and also regarding the localization of vibrational modes. Additionally, the eigendisplacements of characteristic modes of 3-tert-butylcyclohexene have been analyzed.