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141.
Canonical structures in the parametric picture of gravitation in general relativity are investigated. One of the fields, the scalarf, emerges as a secondary entity that interacts with a system consisting of the threemetricg and the connection form. We are employing the (g,) system for developing a canonical approach. While a naïve attempt would appear to founder, we do find an extension of the phase-space of the system which is computationally viable. 相似文献
142.
Jseph Deli Pter Mlnar Gyula Tth Andreas Baumeler Conrad Hans Eugster 《Helvetica chimica acta》1991,74(4):819-824
Cycloviolaxanthin (= (3S,5R,6R,3′S,5′R,6′R)-3.6:3′,6′-Diepoxy-5,6,5′,6′-tetrahydro-β,β-carotene-5,5′-diol), a Novel Carotenoid from Red Paprika (Capsicum annuum) From red paprika (Capsicum annuum var. longum nigrum) cycloviolaxanthin was isolated as a minor carotenoid and, based on spectral data, assigned the symmetrical structure 8 . 相似文献
143.
Ferenc Bertha Gyula Hornyák Károly Zauer Antal Feller Károly Lempert Etelka Pjecka Gabor Tóth 《Tetrahedron》1985,41(14):2855-2860
A method is described for the synthesis of hydrochlorides of some type 8 title compounds in which the nucleophilicity of N-2 is reduced or completely lost so as to prevent ring contraction reactions and, as a result, making these compounds comparatively stable. 相似文献
144.
Z. Homonnay A. Vértes D. L. Beke I. Gödény E. Kuzmann 《Journal of Radioanalytical and Nuclear Chemistry》1989,136(5):371-377
Iron was diffused into aluminium along grain boundaries and studied by Mössbauer spectroscopy. The Mössbauer spectrum of the investigated sample contained one doublet with isomer shift =0.360/5/ mm s–1 /relative to -iron/ and quadrupole splitting =0.84/l/ mm s–1. These results suggest that the iron atoms in the grain boundaries of aluminium have environment very similar to that which is present in amorphous iron /III/ oxides. 相似文献
145.
The hydrogenations of methyl 2-oxoeyclopentanecarboxylate ( 1 ), ethyl 2-oxocyelohexanecarboxylate ( 3 ), and 2-methylcyclohexanone ( 5 ) on unmodified Raney-Ni catalyst lead predominately to the formation of the cis-hydroxy diastereoisomers of 2 , 4 , and 6 , respectively (Scheme 2). In the asymmetric hydrogenations on catalysts modified with chiral tartaric acid ((R, R )-C4H6O6/Raney-Ni and (R, R)-C4H6O6/NaBr/Raney-Ni), the predominance of the cis-isomer increases significantly. The hydrogenations of β-keto esters 1 and 3 proceed with an enantioselectivity of 10–15% on the modified catalysts, while the similar hydrogenation of 5 yields optically inactive 6 . The (1S,2R)-enantiomers of the cis-isomers of 2 and 4 are formed in larger quantity, whereas the (lR,2R)-enantiomers of the corresponding trans-isomers predominate (Scheme 1). The enantioselective formation of trans- 2 and trans- 4 can be interpreted mainly in terms of the asymmetric hydrogenation of cyclic β-keto esters through the keto form, while that of the corresponding cis-hydroxy esters proceeds through the enol form. 相似文献
146.
The 3β-acetoxy-16β,17β-epoxymethyleneandrost-5-ene () transforms into the dihydrooxazine condensed to the sterane skeleton (,,,,,) in a ring-expansion reaction with alkyl and aryl nitriles in the presence of HBF4— diethyletherate The 3β-acetoxy-16α, 17α-epoxymethyleneandrost-5-ene () undergoes a Wagner-Meerwein rearrangement under similar conditions. 相似文献
147.
Judit Kosáry Gyula Jerkovich Katalin Pólos Endre Kasztreiner 《Monatshefte für Chemie / Chemical Monthly》1986,117(6-7):867-874
The novel ring system, 6H-1,2,4-triazino[4,3—b]1,2,4-triazolo[3,4—f]-pyridazine was prepared either by ring closure of1-(1-ethoxycarbonylethylene)-2-(1,2,4-triazolo[4,3—b]pyridazinyl-6)-hydrazine derivatives (4, 5, 7) in polyphosphoric acid or of a hydrazine15 derived from pyridazino-1,2,4-triazine under the action of triethyl orthoformate. Compound8 showed a positive inotropic effect.
Über Pyridazinring enthaltende Verbindungen, 20. 6H-1,2,4-Triazino[4,3—b]1,2,4-triazolo[3,4—f]pyridazin, ein neues angulares Ringsystem
Zusammenfassung Das neue Ringsystem 6H-1,2,4-Triazino[4,3—b]1,2,4-triazolo[3,4—f]-pyridazin wurde entweder durch Ringschluß der1-(1-Ethoxycarbonylethylen)-2-(1,2,4-triazolo[4,3—b]pyridazinyl-6)-hydrazin-Derivate(4, 5, 7) 4, 5, 7 in Polyphosphorsäure, oder aus einem von Pyridazino-1,2,4-triazin abgeleiteten Hydrazin15 durch Ringschluß mit Orthoameisensäuretriethylester hergestellt. Verbindung8 zeigte einen positiven inotropen Effekt.相似文献
148.
Pter Molnr Jzsef Deli Erzsbet sz Ferenc Zsila Mikls Simonyi Gyula Tth 《Helvetica chimica acta》2004,87(8):2159-2168
Circular dichroism (CD) spectroscopy was used to distinguish between the isomeric (all‐E)‐configured 3′‐epilutein ( 2 ) and 6′‐epilutein ( 8 ) to establish the absolute configuration of epilutein samples of different (natural and semisynthetic) origin, including samples of 2 obtained from thermally processed sorrel. Thus, the CD data of lutein ( 1 ) and epilutein samples ( 2 ) were compared. Our results unambiguously confirmed the (3R,3′S,6′R)‐configuration of all epilutein samples. Compound 2 was thoroughly characterized, and its 13C‐NMR data are published herewith for the first time. 相似文献
149.
Katherine M. O'Connor William Henderson Eva O'Neill Damien W. M. Arrigan Stephen J. Harris M. Anthony McKervey Gyula Svehla 《Electroanalysis》1997,9(4):311-315
Two calix[4]arene derivatives, in the partial cone conformation, with sulfur-containing functionalities, were tested as neutral carrier ionophores in potentiometric silver-selective electrodes of conventional membrane and membrane-coated glassy carbon electrode types. Comparison with a calix[4]arene in the cone conformation was made. The membranes were prepared using either 2-nitrophenyl octyl ether or bis(ethylhexyl)sebacate as plasticizers and potassium tetrakis(p-chlorophenyl)borate as the lipophilic salt in a poly(vinyl chloride) matrix. Both calix[4]arenes yielded electrodes of good sensitivity (approx. 47 mV dec−1) in the range 10−4–10−1 M and excellent selectivity [log KAg,MH+ < −1.5] of transition, alkali and heavy metal cations, including sodium, mercury(II) and lead(II) cations. Temperature effects and reproducibility of response were determined and the interfering effects of mercury(II) and lead (II) ions on the membranes were noted. The partial cone conformation allows improved selectivity over certain cations relative to calix[4]arenes in the cone conformation. 相似文献
150.
The tricyclic oxazines 3 and 5 were obtained by ring closure of (2-hydroxymethyl-1-pyrrolidinyl)-3(2H)-pyridazinones 2d,e,g , respectively, prepared from 4,5-dichloro-3(2H)-pyridazinones with L-prolinol. The synthesis of the thiazine analogue 4a was achieved by treatment of 2d with thionyl chloride and the subsequent reaction with sodium sulfide. The structures of the compounds were supported by spectroscopic evidence. 相似文献