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71.
Summary. The sessile drop method has been used to measure density and surface tension for pure Ag, Bi, Sn, and their mixtures. For
pure metals and Bi–Sn alloys negative temperature coefficients of surface tension have been obtained. In case of Ag–Bi and
Ag–Sn alloys the temperature coefficients of surface tension take negative or positive values depending on composition. Experimental
values of the surface tension for Ag–Bi, Ag–Sn, and Bi–Sn are compared with those computed from Butler’s model. A relatively good agreement is observed. 相似文献
72.
The study was performed to compare the effect of magnesium modifier (magnesium nitrate) with that of other modifiers (palladium nitrate and nickel nitrate) in determination of arsenic, antimony and selenium by atomic absorption spectroscopy with atomization in a graphite tube, with generation of hydrides and in situ preconcentration in a graphite tube. The assumed criterion of a modifier performance was the magnitude of the analytical signal. It was found that in determinations with atomization in a graphite furnace the effects of all these modifiers were comparable, while in those with hydride generation and in situ preconcentration in a graphite tube the magnesium modifier showed poorer performance (25% decrease of the analytical signal). In determinations of arsenic and selenium the analytical signal obtained with magnesium salt as a modifier was comparable with those obtained in the presence of all other modifiers. 相似文献
73.
Asymmetric Diels-Alder Reaction of 1-Methoxybuta-1,3-diene with (2R)-N-Glyoxyloylbornane-10,2-sultam
Tomasz Bauer Christian Chapuis Janusz Kozak Janusz Jurczak 《Helvetica chimica acta》1989,72(3):482-486
Starting from sultam 1 , the chiral dienophile (2R)-N-glyoxyloylbornane-10,2-sultam ( 4 ) was readily prepared. Non-catalyzed atmospheric- and high-pressure as well as [Eu(fod)3]-promoted [4 + 2] cycloadditions of 1-methoxy-buta-1,3-diene ( 5 ) to chiral dienophile 4 , leading with high asymmetric induction to 6-methoxy-3,6-dihydro-2H-pyran-2-yl derivatives 6 – 9 , are described. The extent and direction of asymmetric induction in these reactions were established by 1H-NMR analysis and chemical correlation, respectively. Stereochemical models for both non-catalyzed and [Eu(fod)3]-promoted reactions are proposed. 相似文献
74.
Katarzyna Kiegiel Tomasz Baakier Piotr Kwiatkowski Janusz Jurczak 《Tetrahedron: Asymmetry》2004,15(24):3869-3878
The diastereoselective addition of allylsilanes and allylstannanes to N-glyoxyloyl-(2R)-bornane-10,2-sultam 1 and (1R)-8-phenylmenthyl glyoxylate 7 in the presence of Lewis acids has been studied. We obtained diastereoselectivities up to 84% and 94% for the allylation of 2 and 7, respectively. The application of the allylation products of 1 or 2 in the synthesis of 4-butanolides, for example (2S,4S)-2-hydroxy-4-hydroxymethyl-4-butanolide 13 is presented. 相似文献
75.
Iva Blanáriková-HlobilováZuzana Kubánová Lubor Fišera Michal K CyranskiPiotr Salanski Janusz Jurczak Nada Prónayová 《Tetrahedron》2003,59(18):3333-3339
Chiral nitrones derived from l-valine react with methyl acrylate to afford the corresponding diastereomeric 3,5-disubstituted isoxazolidines. The dibenzylsubstituted nitrone gave also 3,4-disubstituted isoxazolidine in 4% yield, additionally. The stereoselectivity was dependent on the steric hindrance of the nitrone and reaction conditions. High pressure decreased the reaction time of the cycloadditions. The major products were found to have the C-3/C-6 erythro and C-3/C-5 trans relative configuration. The major cycloadduct undergoes N-O cleavage and deprotection to a chiral diaminodiol derivative. 相似文献
76.
Jan Romański Julita Jóźwik Christian Chapuis Janusz Jurczak 《Helvetica chimica acta》2007,90(11):2116-2131
Asymmetric 1,3‐dipolar cycloadditions of chiral derivatives of the nitrile oxides 3a – 3c derived from (2R)‐bornane‐10,2‐sultam, (2R)‐10‐(dicyclohexylsulfamoyl)isoborneol, and (1R)‐8‐phenylmenthol, to either (E)‐stilbene 4 or dimethyl fumarate 5 , leading to the corresponding 4,5‐dihydroisoxazoles 6a – 6c and 7a – 7c in both moderate yields and diastereoselectivities, are presented. All cycloadducts were converted into the corresponding methyl esters 8 and 9 , which were used for determination of their enantiomeric purities via chiral HPLC analyses. In the case of both stilbene cycloadducts 6a and 6b , their absolute configurations were determined by X‐ray crystal‐structure analyses. These [3+2] cycloadditions suggest the participation of the thermodynamically less stable SO2/CO syn‐conformer in the πy approach along the C?O bond of the linear nitrile oxide 3a . 相似文献
77.
Z. Urbańczyk-Lipkowska S. Kasprzyk T. Stankiewicz J. Jurczak K. Suwińska 《Journal of chemical crystallography》1993,23(3):185-190
The recent method of synthesis of diazacoronands by macrocyclization of primary,-diamines with dimethyl esters of,-diacids was used for the preparation of the title compound (3).1H and13C NMR in solution, as well as X-ray diffraction studies for three different crystals were undertaken. The centrosymmetric space groupPnma was chosen during structure determination although there are some indications that noncentrosymmetric space groupPna21 is also possible. In solution, dynamically averaged structure with twofold symmetry is observed. In the solid state, two independent molecules in the asymmetric unit show planar symmetry, and are conformationally different. An internal cavity represents a good receptor for a water molecule. Two various hydrogen bonding patterns of different stabilities were found. In the basic pattern, the water oxygen atom is bounded by two amide hydrogen atoms and water molecule uses one of its hydrogen atoms to form an additional hydrogen bond with 01. In the second pattern, water hydrogen atoms are nonbonded. 相似文献
78.
P. Gluziński J. W. Krajewski S. Kasprzyk P. Sałański T. Stankiewicz J. Jurczak 《Journal of chemical crystallography》1992,22(1):15-19
The molecular structure of l,6-diaza-9,12-dioxacyclotetradeca-2,5-dione has been investigated by X-ray and NMR methods. The crystals are monoclinic:C2/c,Z=4,a=8.5571(3),b=14.468(1),c=10.092(2) Å,=113.38(1)°. The structure was solved by direct methods, and refined toR=0.051 on 1082 unique reflections. The molecule exhibits a crystallographic twofold symmetry axis, the axis bisecting the 3C-4C and 10C-11C bonds, which is in full agreement with NMR findings. 相似文献
79.
J. W. Krajewski P. Gluziński P. Sałański S. Kasprzyk T. Stankiewicz J. Jurczak A. Kemme A. Mishnyov 《Journal of chemical crystallography》1992,22(1):9-13
The structure of the title compound has been investigated in the solid state and in solution by X-ray and NMR methods. The crystals are monoclinic:P21/n,a=9.010(2),b=18.877(4),c=9.434(2) Å,=113.06(1)°. The structure was solved by direct methods, and refined with 1764 unique reflections by full-matrix, least-squares toR=0.0607 (R
w
=0.0439). Although a two-fold symmetry of the molecule was suggested from NMR results, no approximate molecular symmetry elements were found in the crystalline state. Some intra- and intermolecular hydrogen bonds were observed. 相似文献
80.
B. Pniewska T. Stankiewicz P. Sałański J. Jurczak 《Journal of chemical crystallography》1995,25(2):69-73
4,7,13,16-tetraoxa-1,10-diaza-5,6-benzocyclooctadeca-11,18-dione, C16H22N2O6·H2O, (3) was synthesized under thermal conditions, starting from ,-diamine (1) and ,-diester (2). The hydrate of compound (3) was investigated in the solid state by X-ray structural analysis. Crystal data: monoclinic system, space group P21/c,a=12.342(4) Å,b=15.978(7) Å,c=8.960(3) Å, =96.72(3)°,Z=4. The structure was solved by direct methods and refined to finalR=0.056,R
w=0.069 for 1962 observed reflections. The structure exhibits internal hydrogen bonds between the etheral O(16) atom and the neighboring amide group. The water molecule connects diamide molecules by one strong hydrogen bond with carbonyl oxygen, and four weak hydrogen bonds with the amide groups and etheral oxygen atoms. 相似文献