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101.
Sándor Balogh Ede Kolos Gaszton Gáll und Pál Kolonits 《Fresenius' Journal of Analytical Chemistry》1975,276(3):201-204
Zusammenfassung Es wurden die Möglichkeiten für die titrimetrische Bestimmung von dimerem Glykolaldehyd (Fp: 94–96° C) und dl-Glycerinaldehyd (Fp: 138–141° C) untersucht. Die systematischen Fehler der auf Grund verschiedener funktioneller Gruppen durchführbaren Messungen sind von der Stabilität ihrer cyclischen Halbacetale sowie von den ihrer Depolymerisation folgenden weiteren Gleichgewichten bestimmt. Das aus dem dl-Glycerinaldehyd gebildete Halbacetal besitzt höhere Stabilität als dasjenige aus dem Glykolaldehyd.Mit der Hydrogensulfit-Methode werden 95–96%, mit der Hydroxylamin-Methode dagegen 98–99% vom wahren Wert gefunden.In Wasser gelöst zersetzt sich der Glykolaldehyd verhältnismäßig rasch, und das Gleichgewicht kann durch beide Aldehydreaktionen quantitativ gegen die Monomerenform verschoben werden.Unsere Untersuchungen ergaben, daß die Hydroxylamin-Methode zur Bestimmung der in Form cyclischer Halbacetale kristallisierenden, dimeren Hydroxyaldehyde Vorteile gegenüber der Hydrogensulfit-Methode bietet.Frau Dipl.-Ing. Eva Varsányi-Kiss danken wir für die derivatographischen Aufnahmen und deren Auswertung. 相似文献
102.
New transesterification reaction between acetylated wood and tetramethoxysilane: A feasibility study 总被引:1,自引:0,他引:1
Novel transesterification of acetylated maritime pine sapwood (Pinus pinaster Soland) reaction was performed with tetramethoxysilane (TMOS) in presence of dibutyltin oxide as a catalyst. Transesterification was confirmed by weight percent gain calculations (WPG), infrared spectroscopy (FTIR) as well as 13C and 29Si NMR CP-MAS analysis. The results showed that transesterification indeed occurs via exchange of acetate groups from acetylated wood and methoxysilane groups from TMOS. The effect of temperatures and reaction time upon transesterification efficiency was also investigated. 相似文献
103.
Allylsilanes show in certain cases a behaviour towards electrophiles which is opposite to that of its carbon homologues. Theoretical calculations using Dewar's MINDO/3 method performed on 3-methyl 3-butenyl trimethylsilane and 2-methyl 2-butene show that geometrical optimization leads to a silicon-allylic carbon bond nearly parallel to the double bond π cloud, and both net atomic charges and HOMO coefficients indicate an inversion between these two substrates. 相似文献
104.
Syntheses and spectral characteristics of cadmium(II) compounds (CdSeO4, CdSeO3, and Cd(NCSe)2(nia)2) containing selenium in oxidation states (VI), (IV), and (-II) are described. In Cd(NCSe)2(nia)2, nicotinamide (nia) and selenocyanate anions are bonded to Cd atom as N-donor monodentate ligands. Nicotinamide is coordinated
through the ring nitrogen atom. The effects of these selenium compounds as well as Cd(NCS)2(nia)2 on the growth and Cd accumulation in roots and shoots of hydroponically cultivated chamomile plants (cultivar Lutea) were studied. In the applied concentration range (12–60 μmol dm−3) Cd(NCS)2(nia)2 affected neither the length nor the dry mass of roots and shoots. Other compounds applied at 24 μmol dm−3 and 60 μmol dm−3 significantly reduced dry mass of roots and shoots. Selenium oxidation state in the cadmium compounds affected Cd accumulation
in plant organs as well as Cd translocation within the plants, which was reflected in the values of bioaccumulation (BAF)
and translocation factors (S/R). Cd amount accumulated by shoots was lower than that in the roots. The highest BAF values
determined for Cd accumulation in shoots were obtained with CdSeO4. Substitution of S with Se in the Cd(NCX)2(nia)2 (X = Se or S) caused an increase of Cd translocation into the shoots.
Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006. 相似文献
105.
A stochastic method of optimization, which combines simulated annealing with simplex, is implemented to fit the parameters of a simple model potential. The main characteristic of the method is that it explores the whole space of the parameters of the model potential, and therefore it is very efficient in locating the global minimum of the cost function, in addition to being independent of the initial guess of the parameters. The method is employed to fit the complex intermolecular potential energy surface of the dimer of water, using as a reference the spectroscopic quality anisotropic site-site potential of Feller et al. The simple model potential chosen for its reparameterization is the MCY model potential of Clementi et al. The quality of the fit is assessed by comparing the geometry of the minimum, the harmonic frequencies, and the second virial coefficients of the parameterized potential with the reference one. Finally, to prove more rigorously the robustness of this method, it is compared with standard nonstochastic methods of optimization. 相似文献
106.
Zusammenfassung Die Reaktion von 1-Nitroso-2-naphthol mit 1-und 2-Naphthol sowie die Reaktion von 2-Nitroso-1-naphthol mit 2-Naphthol in Äthanol und in Äther bei Anwesenheit von HNO3 gibt 5H-Dibenzo[a,j]phenoxazon-(5) (I), 5H-Dibenzo[a,j]phenoxazon-(5)-14-oxid (II), 5H-Dibenzo[a,h]phenoxazon-(5) (III) sowie 5H-Dibenzo[a,h]phenoxazon-(5)-14-oxid (IV). Es wurde ein Reaktionsmechanismus vorgeschlagen und die Konstitution der hergestellten Verbindungen spektrophotometrisch und potentiometrisch bestimmt.
Mit 4 Abbildungen 相似文献
The reaction of 1-nitroso-2-naphthol with 2-and 2-naphthol and the reaction of 2-nitroso-1-naphthol with 2-naphthol in ethanol or ether in the presence of nitric acid have been studied. The main reaction products isolated were the dibenzophenoxazones I–IV. The reaction mechanism for their formation is proposed.
Mit 4 Abbildungen 相似文献
107.
The system BaF2/AlF3 is investigated by X-ray and D.T.A., and the liquid-solid phase diagram is established. Five ternary fluorides are disclosed: trimorphic BaAlF5, Ba3Al2F12, Ba5AlF19, polymorphic Ba3AlF9 and Ba5AlF13. Neutron thermodiffractometry experiments are performed to specify some parts of the diagram. The cell parameters of the fluorides are given and the results are discussed and compared with those of the previous works. 相似文献
108.
Yu. A. Simonov N. V. Gérbéléu P. N. Bourosh V. B. Arion A. D. Garnovskii A. N. Sobolev V. A. Alekseenko 《Journal of Structural Chemistry》1990,31(2):365-369
Institute for Applied Physics, Academy of Sciences of the Moldavian SSR. Institute of Chemistry, Academy of Sciences of the Moldavian SSR. Nat. Research Institute for Physics and Organic Chemistry, Rostov State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 2, pp. 199–202, 1990. 相似文献
109.
Reactivities of homogeneous series of ethylenic compounds R1CHCH21, trans R1CHCHMe 2, R1MeCCH23 and R1CHCMe24 have been measured in methanol at 25°C (R1 Me, Et, n-Pr, -CH2C6H5-CH2OCOCH3, -CH2Cl). The criterion developed to decide between a bridged and a carbonium ion-like transition state is based on an internal comparison of the series and avoids resorting to external structural scales. Even in the case of alkenes 3 and 4 which are very dissymmetric with respect to polarity, the sensitivity to polar effects remains constant and the transition state behaves like a symmetric entity; only a slight secondary effect, attributed to hyperconjugation, is detectable. 相似文献
110.