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Cis Configuration (cis + configuration)

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Chemistry77%

Selected Abstracts

Kinetics and mechanism of the reaction between maleic anhydride and fatty acid esters and the structure of the products

EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 5 2008
Florina Stefanoiu
Abstract Alkenyl succinic anhydrides (ASA) were obtained by reaction between maleic anhydride and high-oleic sunflower oil (HOSO) esters. A kinetics study of the maleinization of alkyl esters indicated that the maleinization reaction was second order overall and first order with respect to the individual reactants, and the activation energy was 77.2,±,3.3,kJ/mol in the investigated temperature range (185,225,°C). These results showed that the cis configuration and the central position of the double bond in HOSO esters facilitate the maleinization of the latter. On the contrary, the length of the linear ester moiety had no influence on the course of the maleinization reaction. Moreover, new evidence demonstrates that there are two different reaction mechanisms: ene-reaction and addition in allylic position with a 2,:,1 ratio, respectively. This ratio was constant throughout the reaction, thus indicating that these mechanisms are independent. [source]

Synthesis and Conformation Analysis of New Perphosphorylated Calix[4]resorcinarenes

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2004
Vera I. Maslennikova
Abstract The octaphosphorylation of calix[4]resorcinarenes 1 by 2-dialkylamino-1,3,2-diheterophosphorinanes 2 is described, and the effect of different factors on the structures of the resulting perphosphorylated products 3,5 was studied. Conformation analysis of these compounds by correlated 2D NMR spectroscopy and X-ray diffraction analysis was performed, and it was found that compounds 3,5, like the initial resorcinarenes 1, each have the all - cis configuration of the R groups in the methylidene bridges of the calixarene system, but different orientations of benzene rings and phosphorinane fragments with respect to one another and to the macrocycle plane. Perphosphorylated resorcinarenes 3a,c, 4a and 5a with R = alkyl exist in flattened cone conformations with the phosphorinane fragments on the same side of the macrocycle plane. The conformations of the perphosphorylated resorcinarenes 3d, 4b and 5b with R = Ph change to forms intermediate between flattened cone and 1,3 - alternate. The phosphorus fragments in these compounds are located on opposite sides of the macrocycle plane. It was shown that the oxidation and sulfurisation of phosphocalixarenes 3 proceed without any change in the spatial organisation of the macrocyclic system. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Cycloaddition Behavior of 1,2-Thiaphospholes: Reactions with Diazocumulenes and with Cyclopentadiene

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2003
Jochen Kerth
Abstract 1,2-Thiaphospholes 3a,b react with (1-diazo-2-oxoalkyl)silanes 1a,c to form [1,2]thiaphospholo[2,,3,:3,4][1,3]diphospholo[1,5- b][1,2]thiaphosphole systems 4 with cis - anti - cis configuration of the tricyclic framework. They are accompanied by small amounts of compounds 5 that are presumably the cis - syn - cis isomers of 4, and 6-alkylidene-1-phospha-2-thiabicyclo[3.1.0]hex-3-enes 6. It is likely that these reactions proceed by [3+2] cycloaddition of diazocumulenes, which coexist with diazo compounds as minor equilibrium components, at the P=C bond of the heterophospholes, followed by N2 elimination and formation of short-lived 2-alkylidene-1,2(,5)thiaphospholes. The latter can either add to excess thiaphosphole to form the tricyclic products or undergo electrocyclization to form bicyclic alkylidenephosphiranes. Thiaphosphole 3a does not seem to react directly with cyclopentadiene in a [4+2] or [2+4] cycloaddition. Reaction with excess cyclopentadiene at 120 °C yields the polycyclic compounds 15 and 16, which are likely to arise from a Diels,Alder reaction of 3a, reacting as a heterodiene, with the cyclopentadiene dimer. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Structural characterization of cyclic kallidin analogues in DMSO by nuclear magnetic resonance and molecular dynamics

JOURNAL OF PEPTIDE SCIENCE, Issue 1 2005
Elisabetta Schievano
Abstract The conformational properties in DMSO of two head-to-tail cyclic analogues of kallidin ([Lys0]-bradykinin, KL) as well as those of the corresponding linear peptides were studied by NMR and molecular dynamics (MD) simulations. The modifications in the sequence were introduced at position 6, resulting in the four peptides, [Tyr6]-KL (YKL), [Trp6]-KL (WKL), cyclo-([Tyr6]-KL) (YCKL) and cyclo-([Trp6]-KL) (WCKL). The linear WKL analogue was significantly more potent than kallidin on rat duodenum preparations, whereas YKL was significantly less potent. Both cyclic peptides, YCKL and WCKL displayed similar activity, lower than that of the linear analogues and also of cyclo-KL. The two linear analogues display high conformational flexibility in DMSO. In the predominant conformer, for both peptides, all three X-Pro bonds adopt a trans configuration. Three out of four conformers present in YCKL and WCKL were completely assigned. The configurations at the X-Pro bonds are the same for the two analogues. All cyclic conformers show a cis configuration in at least one X-Pro bond and always opposite configuration for the two consecutive X-Pro bonds. The NOE-restrained MD calculations resulted in the detection of several elements of secondary structure in each of the conformers. Such elements are described and their possible relevance to biological activity is discussed. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd. [source]

Synthesis of a new zirconium catalyst for ethylene polymerization

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2008
Fabiana De C. Fim
Abstract A novel complex dichlorobis(2-ethyl-3-hydroxy-4-pyrone)zirconium(IV) (ZrCl2(ethylpyrone)2) was synthesized. Complexation of the pyrone ligand to the zirconium was confirmed by UV, 1H and 13C-NMR, and electrochemical studies. NMR showed the presence of four isomers and density functional theory calculations indicated that the main isomer had a cis configuration. The catalyst was shown to be active in ethylene polymerization in the presence of the cocatalyst methylaluminoxane. The highest catalyst activity for the zirconium complex was achieved at Al/Zr = 2500, 70 °C and when a small concentration of catalyst was used (1 ,mol). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3830,3841, 2008 [source]

Application of electrochemically generated molybdenum-based catalyst system to the ring-opening metathesis polymerization of norbornene and a comparison with the tungsten analogue

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 7 2005
Okan Dereli
Abstract This study describes the application of the electrochemically generated molybdenum-based catalyst system MoCl5e,AlCH2Cl2 to ring-opening metathesis polymerization of bicyclo[2.2.1]hept-2-ene (norbornene). The results are compared with those previously obtained by the WCl6e,AlCH2Cl2 system. The polymer product has been characterized by 1H and 13C NMR, IR and gel-permeation chromatography techniques. This molybdenum-based catalyst system has led to a mainly trans stereoconfiguration (ca 60%) of the double bonds, in contrast to the polymer obtained with the tungsten-based analogue, where the cis content is 60%. Analysis of the poly(1,3-cyclopentylenevinylene) microstructure by 13C NMR spectroscopy revealed that the polymer having ,c = 0.41 (fraction of double bonds with cis configuration) contains a slightly blocky distribution (rtrc > 1) of the double-bond dyads (rtrc = 1.44). In addition, the influence of reaction parameters, e.g. reaction time, electrolysis time and catalyst aging time, on conversion has been analysed in detail. Copyright © 2005 John Wiley & Sons, Ltd. [source]

[N,N,-Bis­(salicyl­idene)-2,2-di­methyl-1,3-propane­diaminato]­nickel(II) and [N,N,-bis­(salicyl­idene)-2,2-di­methyl-1,3-propane­diaminato]copper(II)

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2001
Cengiz Arici
In the title compounds, {2,2,-[2,2-di­methyl-1,3-propane­diyl­bis­(nitrilo­methyl­idyne)]­diphenolato-,4N,N,,O,O,}nickel(II), [Ni(C19H20N2O2)], and {2,2,-[2,2-di­methyl-1,3-propane­diyl­bis­(nitrilo­methyl­idyne)]­diphenolato-,4N,N,,O,O,}copper(II), [Cu(C19H20N2O2)], the NiII and CuII atoms are coordinated by two iminic N and two phenolic O atoms of the N,N,-bis­(salicyl­idene)-2,2-di­methyl-1,3-propane­diaminate (SALPD2,, C17H16N2O22,) ligand. The geometry of the coordination sphere is planar in the case of the NiII complex and distorted towards tetrahedral for the CuII complex. Both complexes have a cis configuration imposed by the chelate ligand. The dihedral angles between the N/Ni/O and N/Cu/O coordination planes are 17.20,(6) and 35.13,(7)°, respectively. [source]

(2R,3R,5R)-2-[(2R,3aS,6aR)-2,3,3a,4,5,6a-Hexa­hydro­furo­[2,3- b]­furan-2-yl]-5-isoprop­en­yl-2,3-di­methyl­cyclo­hexanone and (4aR,5S,7R)-5-isopropenyl-7,8,8-tri­methyl-2,3,4,4a,5,6,7,8-octa­hydro­naphthalene-4a-carbo­nitrile

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2000
Dianne D. Ellis
The molecular structures of two chiral cyclo­hexanones based on R -(,)-carvone, C17H26O3, (I), and C17H23NO, (II), are reported here. The six-membered ring in (I) is in a chair conformation with the two fused five-membered rings of the furo­furan­yl substituent in a cis configuration. Compound (II) contains a decalin group; one ring has the chair form whilst the other is in a half-boat conformation. Both products have been characterized spectroscopically, however, neither NMR nor IR results could prove the stereochemistry at each chiral centre unambiguously. The crystal analyses were used to ex­amine conformational properties of the compounds. [source]

Configurations of Nickel,Cyclam Antiviral Complexes and Protein Recognition

CHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2007
Tina M. Hunter
Abstract Nickel(II),xylylbicyclam is a potent anti-HIV agent and binds strongly to the CXCR4 co-receptor. We have investigated configurational equilibria of NiII,cyclam derivatives, since these are important for receptor recognition. Crystallographic studies show that both trans and cis configurations are readily formed: [Ni(cyclam)(OAc)2],H2O adopts the trans -III configuration with axial monodentate acetates, as does [Ni(benzylcyclam)(NO3)2] with axial nitrate ligands, whereas [Ni(benzylcyclam)(OAc)](OAc),2,H2O has an unusual folded cis -V configuration with NiII coordination to bidentate acetate. UV/Vis and NMR studies show that the octahedral trans -III configuration slowly converts to square-planar trans -I in aqueous solution. For NiII,xylylbicyclam, a mixture of cis -V and trans -I configurations was detected in solution. X-ray diffraction studies showed that crystals of lysozyme soaked in NiII,cyclam or NiII2,xylylbicyclam contain two major binding sites, one involving NiII coordination to Asp101 and hydrophobic interactions between the cyclam ring and Trp62 and Trp63, and the second hydrophobic interactions with Trp123. For NiII,cyclam bound to Asp101, the cis -V configuration predominates. [source]