Synthesis,structure, and characteristics of 1,2-dichlorovinyl alkyl ketones

A method of alkyl 1,2-dichlorovinyl ketones preparation from acyl halides and 1,2-dichloroethylene was developed. The configurational equilibrium and electronic structure of alkyl 1,2-dichlorovinyl ketones was investigated by IR, ¹H and ¹³C NMR spectroscopy, by measuring dipole moments, and by quantum-chemical calculations using methods RHF and B3LYP in the basis 6–311++G (d,p). Alkyl 1,2-dichlorovinyl ketones are stable in the Z, s-cis-configuration where the olefin proton is involved into an intramolecular hydrogen bond with the oxygen of the carbonyl group. Reaction of 1,2-dichlorovinyl ketones with alkylhydrazines afforded 1-alkyl-3-alkyl-4-chloropyrazoles. The reaction of alkyl 1,2-dichlorovinyl ketones with 1,1-dimethylhydrazine involved dehydrochlorination and afforded 1,1-dimethylhydrazinium hydrochloride and a mixture of compounds with uncertain structure.Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 11, 2004, pp. 1632–1640.Original Russian Text Copyright © 2004 by Bozhenkov, Leckovskaya, Larina, Ushakov, Dolgushin, Mirskova.     

Ultrafast transient lens spectroscopy of various C40 carotenoids: lycopene, beta-carotene, (3R,3'R)-zeaxanthin, (3R,3'R,6'R)-lutein, echinenone, canthaxanthin, and astaxanthin

The ultrafast internal conversion (IC) dynamics of seven C(40) carotenoids have been investigated at room temperature in a variety of solvents using two-color transient lens (TL) pump-probe spectroscopy. We provide comprehensive data sets for the carbonyl carotenoids canthaxanthin, astaxanthin, and-for the first time-echinenone, as well as new data for lycopene, beta-carotene, (3R,3'R)-zeaxanthin and (3R,3'R,6'R)-lutein in solvents which have not yet been investigated in the literature. Measurements were carried out to determine, how the IC processes are influenced by the conjugation length of the carotenoids, additional substituents and the polarity of the solvent. TL signals were recorded at 800 nm following excitation into the high energy edge of the carotenoid S2 band at 400 nm. For the S2 lifetime solvent-independent upper limits on the order of 100-200 fs are estimated for all carotenoids studied. The S1 lifetimes are in the picosecond range and increase systematically with decreasing conjugation length. For instance, in the sequence canthaxanthin/echinenone/beta-carotene (13/12/11 double bonds) one finds tau1 approximately 5, 7.7 and 9 ps for the S1-->S0 IC process, respectively. Hydroxyl groups not attached to the conjugated system have no apparent influence on tau1, as observed for canthaxanthin/astaxanthin (tau1 approximately 5 ps in both cases). For all carotenoids studied, tau1 is found to be insensitive to the solvent polarity. This is particularly interesting in the case of echinenone, canthaxanthin and astaxanthin, because earlier measurements for other carbonyl carotenoids like, e.g., peridinin partly showed dramatic differences. The likely presence of an intramolecular charge transfer state in the excited state manifold of C40 carbonyl carotenoids, which is stabilized in polar solvents, has obviously no influence on the measured tau1.     

Gas permeability of polydimethylsiltrimethylene above and below the melting temperature of the crystalline phase

The gas-separation behavior of a semicrystalline polydimethylsiltrimethylene—one of the family of silmethylene rubbers—has been studied. The permeability of O₂, N₂, and CH₄ through this polymer at temperatures below and above the melting temperature of the crystalline phase has been investigated, and the activation energy of permeability has been calculated. The gas permeability of the semicrystalline polydimethylsiltrimethylene depends on the prehistory of the sample. At the melting temperature of crystals, the permeability coefficients of the tested gases increase sharply. The transition of the polymer from the semicrystalline state to the melt leads to an appreciable reduction in the activation energy of permeability.     

Preparation of silyl derivatives of unsaturated carbocyclic compounds by the Diels-Alder reaction of 1,2-dimethylenecyclobutane and vinylsilanes

The Diels-Alder reactions of 1,2-dimethylenecyclobutane with vinyltrichlorosilane and vinylmethyldichlorosilane give the corresponding trichlorosilyl and methyldichlorosilyl derivatives of cyclobutene. Methylation of these derivatives gave 4-trimethylsilylbicyclo[4.2.0]oct-1-ene, which underwent thermal isomerization to 4-trimethylsilyl-1,2-dimethylcyclohexane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 943–945, April, 1991.     

Formation of a grating of submicron nematic layers by photopolymerization of nematic-containing mixtures

A submicron, spatially periodic, structure consisting of a sequence of oriented layers of a nematic liquid crystal (NLC), separated by isotropic polymeric walls, was obtained experimentally. This was accomplished by polymerization induced by the interference pattern of UV laser radiation in a NLC-containing prepolymer mixture. It was established that such a structure occurs when phase separation and nematic ordering are prevented during the polymerization process. These structures are the diffraction elements, whose efficiency is much greater than that of a standard grating of polymer-dispersed liquid crystals [1–4] which is obtained in the same initial mixture. Specifically, a diffraction efficiency of 60–70% was obtained for structures with the period Δ = 0.2 μm, even in mixtures where a grating with Δ < 6 μm cannot be obtained at all by the standard technique.     

Peculiarities of NMR spectra of heterospin complexes

Experimental investigation and theoretical simulation of the unusual phenomenon of multiple broadening and narrowing of NMR signals due to the temperature variation of a solution of the stereochemically non-rigid heterospin Ni²⁺ complex with stable nitroxide were performed. The investigation of the temperature dependence of the NMR signals of stereochemically non-rigid heterospin systems can be used for choosing conditions for growing heterospin single crystals containing molecules in a definite conformation.     

Reactions of Pyrrole-1- and Pyrrole-2-carbodithioates with Activated Acetylenes

Pyrrole-1- and pyrrole-2-carbodithioates react with activated alkenes (KOH-DMSO, room temperature) along the nucleophilic addition mechanism regio- and stereospecifically to afford pyrrole-1-and pyrrole-2-carbodithioethenes. The adducts of pyrrole-2-carbodithioates under the reaction conditions undergo intramolecular cyclization into pyrrolothiazoles derivatives.     

Electrospray ionization multiple-stage tandem mass spectrometric analysis of diglycosyldiacylglycerol glycolipids from the bacteria Bacillus pumilus

Electrospray ionization (ESI) combined with multiple-stage tandem mass spectrometry (MS(n)) was used to directly analyze the glycolipid mixture from bacteria Bacillus pumilus without preliminary separation. Full scan ESI-MS revealed the composition of picomole quantities of glycerolglycolipid species containing C(14)-C(19) fatty acids, some of which were monounsaturated. Two main components were identified from their molecular masses and fragmentation pathways. The fragmentation pathway of the known compound compared with the investigated compound verified the proposed structure as 1(3)-acyl-2-pentadecanoyl-3(1)-O-[beta-D-glucopyranosyl-(1-->6)-O-beta-D-glucopyranosyl]-sn-glycerols. A comparison of the multiple tandem mass spectra of the different alkali-metal cation adducts indicates that the intensity of fragments and the dissociation pathways are dependent on the alkali-metal type. The basic structures of glycerolglycolipids were reflected clearly from the fragmentation patterns of the sodium cations. The intense fragments of the sugar residue from the precursor ions were obtained from the lithiated adduct ions. ESI-MS(n) spectra of [M + K](+) ions did not provide as much fragmentation as [M + Na](+) and [M + Li](+) adducts, but their spectra allow the position of glycerol acylation to be determined. On the basis of MS(2) spectra of [M + K](+) ions, it was established that all components have a C(15:0) fatty acid at the sn-2 position of the glycerol backbone and C(14)-C(19) acids at the sn-1 position of the glycerol backbone. Copyright 1999 John Wiley & Sons, Ltd.     

Kurchatov Synchrotron Radiation Source Upgrade Project

Crystallography Reports - The National Research Centre “Kurchatov Institute” has started a project aimed at upgrading the synchrotron radiation source. On the basis of the existing...