Geometrical isomerism and photochemical behaviour of α-substituted 2 and 4-styrylpyridines

α-Methyl and α-phenyl substituted 2 and 4-styrylpyridines were prepared by classical routes. The geometrical isomers were separated and characterized on the basis of their U.V. absorption spectra and/or of their behaviour under U.V. irradiation which led to photoisomerization and photocyclization products. The last photoreaction, in the case of α-phenyl derivatives, gave pyridyl-substituted phenanthrenes and phenyl-substituted azaphenanthrenes which were isolated and characterized. Spectral, chromatographic and physical properties of trans and cis derivatives and related photocyclization products are given as well as some kinetic data for the photochemical reactions.     

Synthesis and some properties of cyclic acetals of malonaldehyde

The Lewis acid-catalyzed addition of cyclic orthoformates to vinyl ethyl ether, which leads to the formation of malonaldehyde acetals, was studied. It is shown that of the linear-cyclic malonaldehyde acetals, 2-(2,2-diethoxyethyl)- and 5,5-dimethyl-2-(2,2-diethoxyethyl)-1,3-dioxanes are stable. The transacetalization of 1,1,3,3-tetraethoxypropane with 1,2- and 1,3-diols, which leads to the formation of cyclic malonaldehyde acetals, was studied. The physicochemical constants of the acetals were determined, and their ¹H and ¹³C NMR spectra are described.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 459–463, April, 1983.     

The stereoselective α-alkylation of chiral β-hydroxy esters and some applications thereof

The stereoselectivity of the α-alkylation of chiral β-hydroxy ester is discussed. The configuration of the alkylated product was proved chemically (Scheme 2). A one pot aldol-alkylation reaction was developed leading stereoselectively to racemic (s*,s*)-α-alkyl-β-hydroxy ester (Scheme 3,4). Baker's yeast reduction of 2-alkyl-3-keto ester led to valuable chiral (2RS,3S)-intermediates, which were converted via the corresponding dianion to compounds with a chiral quaternary C atom (Scheme 6). Synthetic applications of the above findings are shown in the synthesis of various chiral compounds (Scheme 8 and 9).     

Konformationen von 1,3-dioxanen nach der kraftfeldmethode. nichtbindende wechselwirkungen von sauerstoff

The treatment of oxygen lone pairs in force field calculations is discussed. The geometries of 1,3-dioxanes can be calculated well without explicit account of lone pairs. For the calculation of conformational energies in 5-alkyl-1,3-dioxanes electrostatic interactions between point charges taken from quantum mechanical calculations must be included. Addition of van der Waals interactions of lone pairs as weak potentials further improves the calculated conformational energies.     

Characteristics of vinyl iodide microwave plasma etching of GaAs/AlGaAs and InP/InGaAs heterostructures

Vinyl iodide (C₂H₃I) microwave discharges with additions of H₂ and Ar are found to provide faster etch rates than conventional CH₄/H₂/Ar discharges for InP, InGaAs, GaAs, and AlGaAs. This is a result of the relatively high volatilities of indium, gallium, and aluminum iodide species. The etched features are smooth and anisotropic over a wide range of do self-biases (–150 to –350 V), process pressures (1–20mTorr), and microwave powers (150–500 W). The polymer that forms on the mask during the plasma exposure can be readily removed in O₂ discharges. Electron spectroscopy for chemical analysis (ESCA) showed that the etched surfaces are slightly deficient in the group V elements under most conditions, but changes to the optical properties of the semiconductors are minimal. No defects are visible by transmission electron microscopy (TEM) in GaAs or InP samples etched at dc biases –250 V.     

An electrochemical study of redox indicators : Part I. Substituted chrysoidines

The electrochemical oxidation of various substituted chrysoidines was studied by cyclic voltammetry, to determine which have stable oxidation products. Only 4-hydroxy-chrysoidine has a stable product; the apparent oxidation potential is 0.779 V vs. NHE. 4-Methoxy- and 4-ethoxy-chrysoidine rapidly lose methanol or ethanol, respectively, so that the 4-hydroxychrysoidine wave appears on subsequent scans. All the other chrysoidines studied are irreversible. The results indicate that a hydroxy group in the 4-position is necessary for stability; the 4-alkoxychrysoidines can achieve the stable quinoidal structure by cleavage of the alkoxy group after nucleophilic attack.     

A new spot test for cerium(IV)

Summary A new colour reaction for the detection of cerram(IV) which can be carried out both in a test tube and on a spot plate has been described. The test solution is treated with methylene blue in nitric acid solution (11) to form a rose-red colour. This simple procedure has an advantage over the existing tests in that it is applicable in the presence of oxidising agents like chromium(VI), vanadium(V), nitrate, perchlorate and of coloured ions like copper(II), cobalt(II), nickel(II), chromium(III), iron(III), vanadium(IV), uranium(VI).

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Zusammenfassung Eine neue, sowohl in der Eprouvette wie auf der Tüpfelplatte ausführbare Farbreaktion zum Nachweis von Cer(IV) wurde angegeben. Die Probelösung wird mit salpetersaurer Methylenblaulösung behandelt und gibt eine rosarote Färbung. Die Reaktion hat gegenüber bekannten Tests den Vorteil, in Gegenwart von Oxydationsmitteln wie Cr(VI), V(V), NO₃ ^–, ClO₄ ^– bzw. in Anwesenheit gefärbter Ionen wie Cu(II), Co(II), Ni(II), Cr(III), Fe(III), V(IV) oder U(VI) anwendbar zu sein.

     

Metallionen und H2O2. V. Über Struktur und Aktivität der den H2O2-Zerfall katalysierenden Cu2+-Komplexe III. Versuche zur Lösung von Strukturproblemen mit Hilfe der Katalyseeigenschaften

The catalytic properties of Cu²⁺-chelates of the following ligands in H₂O₂ decomposition have been investigated: N, N′-diglycyldiaminoethane (I), N, N′-diglycyl-1,5-diaminopentane (II), N, N′-diglycyl-1,3-diaminopropane (III) [6], glycinamide (IV), glycylglycinamide (V) and polymyxin B (VI). It is confirmed that the catalysis of H₂O₂ decomposition by Cu²⁺-chelates and the formation of ternary peroxo complexes (absorbing at 360 nm) depend on the number of free coordination positions. It is now shown that in reversal the number of free coordination positions on the Cu²⁺ in its complexes can be determined by measuring their catalytic activity on the H₂O₂ decomposition, and their absorption at 360 nm.     

Film formation from pure and mixed latices; transient fluorescence study

A fast transient fluorescence technique was used to study latex film formation induced by organic solvent vapor. Mixtures of pyrene (P)- and naphthalene (N)-labeled and/or pure naphthalene-labeled latex films were prepared separately from poly(methyl methacrylate) (PMMA) particles. Then these pure and mixed latex films were exposed to vapor of various chloroform-heptane mixtures in seven different experiments. In both films, fluorescence lifetimes from N were monitored during vapor-induced film formation. It was observed that N lifetimes decreased as the vapor exposure time is increased. A Stern-Volmer kinetic analysis was used for low quenching efficiencies to interpret the decrease in N lifetimes. A Prager-Tirrell model was employed to obtain back-and-forth frequencies, nu, of reptating PMMA chains during latex film formation induced by solvent vapor. In both pure and mixed latex films, nu values were found to be correlated with the chloroform content in the vapor mixture. It was observed that polymer interdiffusion obeyed a t1/2 law during film formation.