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Geometrical Isomers (geometrical + isomer)

Distribution by Scientific Domains

Chemistry	75%

Selected Abstracts

N -(Aryl)picolinamide Complexes of Ruthenium: Usual Coordination and Strategic Cyclometalation

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2007
Sumon Nag
Abstract Reaction of five N -(4- R -phenyl)picolinamides (R = OCH3, CH3, H, Cl, and NO2) with [Ru(PPh3)2(CO)2Cl2] in refluxing 2-methoxyethanol in the presence of a base (NEt3) affords two geometrical isomers of a group of complexes (1-R and 2-R), each of which contains an amide ligand coordinated to the metal center as a monoanionic bidentate N,N donor along with two triphenylphosphanes, a carbonyl, and a hydride. Similar reaction of N -(naphthyl)picolinamide with [Ru(PPh3)2(CO)2Cl2] affords an organometallic complex, 3, in which the amide ligand is coordinated to the metal center, by C,H activation of the naphthyl ring at the 8-position, as a dianionic tridentate N,N,C donor along with two triphenylphosphanes and one carbonyl. Structures of the 1-OCH3, 2-CH3, and 3 complexes have been determined by X-ray crystallography. In all the complexes the two triphenylphosphanes are trans. In the 1-R complexes the hydride is trans to the pyridine nitrogen and in the 2-R complexes it is trans to the amide-nitrogen. All the complexes are diamagnetic, and show characteristic 1H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a RuII,RuIII oxidation within 0.71,0.93 V versus SCE. An oxidation and a reduction of the coordinated amide ligand are also observed within 1.29,1.69 V versus SCE and ,1.02 to ,1.21 V versus SCE respectively.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Geometrical isomerisation of eicosapentaenoic and docosahexaenoic acid at high temperatures

EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 7 2006
Svein A. Mjøs
Abstract Concentrates of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were heated at 140,240,°C for 2,8,h under nitrogen. The trans isomers were analysed by gas chromatography-mass spectrometry on a BPX-70 cyanopropyl column. All geometrical isomers of EPA and DHA with one trans double bond were observed. The rate constants (k) for the isomerisation of the all- cis isomers were calculated and found to be higher than previously reported for linoleic acid and ,-linolenic acid. Arrhenius plots showed a linear relationship between ln,k and the reciprocal absolute temperature above 180,°C. The distribution patterns of isomers with one trans double bond are approximately constant up to a degree of isomerisation of 25%. The degree of isomerisation can therefore be estimated from selected trans peaks. [source]

Simultaneous HPLC-DAD-MS (ESI+) determination of structural and geometrical isomers of carotenoids in mature grapes,

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2010
Pasquale Crupi
Abstract Carotenoids are uniquely functional polyene pigments ubiquitous in nature; aside from being responsible for the color of a wide variety of vegetables, interest is being focused on food carotenoids due to their likely health benefits. From analytical point of view, it is important to unequivocally identify individual carotenoid compounds in many food stuffs. Therefore, isolation of standards from natural sources must be encouraged for accurate identifications. Like many fruits, mature grape berries contain numerous carotenoid compounds, mostly found in the skin at levels two to three times higher than in the pulp. Carotenoid compounds in a typical wine grape variety (Negroamaro) grown in Apulian region were investigated by reversed-phase C30 (RP-30) HPLC-DAD-MS (ESI+) analysis. As a consequence of an unusual ionization process of carotenoids, their mass spectra registered in the positive ion mode comprised both protonated molecules and molecular ion radicals with little fragmentation. Additionally, selective collision-induced dissociation (CID) experiments, together with fine structures of the UV,vis spectra, were used to differentiate structural and geometrical isomers. This technique allowed the simultaneous determination of regio- and cis -isomers of lutein (zeaxanthin, 9Z and 9,Z -lutein) and a cis -isomer of ,-carotene (9Z - ,-carotene), 5,6-epoxy xanthophylls (violaxanthin, (9,Z)-neoxanthin, lutein-5,6-epoxide) and 5,8-epoxy xanthophylls diasteroisomers (neochrome, auroxanthin, luteoxanthin, flavoxanthin, chrysanthemaxanthin). Copyright © 2010 John Wiley & Sons, Ltd. [source]