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71.
[reaction: see text] Photochemically generated nitrate radicals (NO(3)(*)) cleave the stereoisomeric N,N-dimethyl-substituted uracil cyclobutane dimers 1a-d into the monomeric uracil derivative 2 as the major reaction pathway. A preferred splitting of the syn dimers 1a,b was observed. The reaction is expected to proceed through initial one-electron oxidation with formation of an intermediate cyclobutane radical cation 11. In addition to cycloreversion, competing reaction steps of 11, which lead to the observed byproducts, are suggested. 相似文献
72.
J. Krägel J. B. Li R. Miller M. Bree G. Kretzschmar H. Möhwald 《Colloid and polymer science》1996,274(12):1183-1187
The surface viscoelastic properties of monolayers of two phospholipids DPPC (L--dipalmitoylphosphatidylcholine) and DMPE (L--dimyristoylphosphatidyl-ethanolamin), at the air-water interface have been investigated. Two techniques were used for the investigation. One involved use of an interfacial shear rheometer (torsion pendulum apparatus ISR1), to provide measurements of the shear viscosity s as a function of surface pressure, and the second, a modified LB trough with an oscillating barrier to generate periodie dilation and compression so as to measure the dilational elastic modulusE as a function of surface area.Results indicate a strong dependence of s andE upon monolayer phases. This suggests that the viscoelastic relaxation of monolayers can be understood as molecular rearrangements, domain exchange and molecular reorientations between different monolayer states. 相似文献
73.
F. Petzoldt K. Piglmayer W. Kräuter D. Bäuerle 《Applied Physics A: Materials Science & Processing》1984,35(3):155-159
Lateral growth rates of Ni spots deposited on absorbing substrates by decomposition of Ni(CO)4 with visible Kr+ laser light have been measured. The experimental data are consistent with the calculated temperature distributions. The mechanism of decomposition is thermal with an apparent chemical activation energy of 22±3 kcal/mole for the temperature range 350 KT500 K. 相似文献
74.
Bei der Umsetzung von Acetylchlorid mit Cylopentadien entstehen zwei leicht isolierbare Isomere C9H10O2. Das tiefer schmelzende Isomere ist o-Diacetyl-cyclopentadien, das als Monoenol (I) vorliegt.
6. Mitt., Mh. Chem.90, 571 (1959).—Über o-Diacetyl-benzol vgl. 9. Mitt., Mh. Chem.90, 579 (1959). Frühere Literatur ebenda.
Gleichzeitig 4. Mitt. der Reihe Substitutionsprodukte des Cyclopentadiens; 3. Mitt., Mh. Chem.90, 568 (1959). 相似文献
6. Mitt., Mh. Chem.90, 571 (1959).—Über o-Diacetyl-benzol vgl. 9. Mitt., Mh. Chem.90, 579 (1959). Frühere Literatur ebenda.
Gleichzeitig 4. Mitt. der Reihe Substitutionsprodukte des Cyclopentadiens; 3. Mitt., Mh. Chem.90, 568 (1959). 相似文献
75.
The core structure of the complex pentacyclic 5,11-methanomorphanthridine alkaloids is constructed stereospecifically in one step employing an intramolecular [3 + 2]-cycloaddition of nonstabilized azomethine ylide as the key step. The strategy is demonstrated by accomplishing the formal total synthesis of (+/-)-pancracine. [reaction: see text] 相似文献
76.
The conditions of thermal decomposition of Y, La and lanthanide (from Ce(III) to Lu) pyromucates have been studied. On heating, these complexes decompose in various ways: La, Pr, Nd and Sm pyromucates in four stages, Ce, Eu, Gd, Dy, Ho and Er pyromucates in three stages, and Tm, Yb, Lu and Y pyromucates in two stages, the oxides finally being formed. The hydrated complexes (from La to Er) lose crystallization water to form anhydrous salts. The anhydrous complexes of La, Pr, Nd and Sm decompose to oxides through the intermediate formation of unstable oxypyromucates and Ln2O2CO3, whereas the anhydrous complexes of Ce(III), Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu decompose to the oxides through the intermediate formation of oxypyromucates. The temperatures of dehydration and oxide formation change periodically with increasing atomic number in the lanthanide series.
Zusammenfassung Die Bedingungen der thermischen Zersetzung der Pyromucate von Y, La und den Lanthaniden (Ce(III) bis Lu) wurden untersucht. Beim Erhitzen zersetzen sich die Komplexe auf verschiedene Weise: die Pyromucate von La, Pr, Nd und Sm in 4 Schritten, die von Ce, Eu, Gd, Dy, Hod Er in 3 Schritten und die von Tm, Yb, Lu und Y in nur 2 Schritten. Endprodukte der Zersetzung sind die Oxide, Die hydratisierten Komplexe von La bis Er verlieren Kristallwasser unter Bildung der wasserfreien Salze. Die wasserfreien Komplexe von La, Pr, Nd und Sm zersetzen sich zu Oxiden über instabile Oxypyromucate und Ln2O2CO3 als Zwischenprodukte, bei der Zersetzung der wasserfreien Komplexe von Ce(III), Eu, Gd, Dy, Ho, Er, Tm, Yb und Lu werden Oxypyromucate als Zwischenprodukte gebildet. Die Temperaturen der Dehydratisierung und Oxidbildung schwanken periodisch mit ansteigender Atomzahl in der Lanthanidenreihe.
, ( ) . : , , , , , , , — , , , — . , . , , Ln2O2CO3. . .相似文献
77.
Piotr Król Bożena Król Stanisław Pikus Maciej Kozak 《Colloid and polymer science》2006,285(2):169-175
Small angle X-ray scattering and differential scanning calorimetry methods were employed to characterise the internal order of structural phases present in polyurethane coatings obtained as a result of water evaporation from anionomer dispersions. Those anionomers were produced in the reaction of aromatic, cycloaliphatic and aliphatic diisocyanates with polyoxyethylene glycol, 2,2-bis-(hydroxymethyl)propionic acid and 1,6-hexamethylenediamine. The decisive effects were found from ionic and polar structures within the rigid urethane and urea segments on the ordered arrangement degree of the supermolecular structures in the obtained anionomers. That becomes apparent in differential scanning calorimetry thermograms and contributes to improved thermal stability of the produced polyurethane coatings. 相似文献
78.
Ganesh Suyal Martin Mennig Helmut Schmidt 《Journal of Sol-Gel Science and Technology》2004,29(1):11-18
A sol-gel route to synthesize nanocomposite thin films containing phase separated metal colloids of gold (Au) and silver (Ag) was developed. Ag—Au colloids were prepared in silica films using dip coating technique. The annealing of the samples in air results in the formation of phase separated Ag and Au colloids in SiO2 thin films, showing the surface plasmon peaks at 410 nm and 528 nm. For the synthesis of phase separated Ag and Au colloids on float glass substrates, formation of the silver colloids was found strongly dependent on the surface of the float glass. On the tin rich surface formation of both gold and silver colloids took place, whereas, on the tin poor surface the formation of only gold colloids was observed. The surface dependence of the formation of silver colloids was attributed to the presence of tin as Sn2+ state on the glass surface, which oxidizes into Sn4+ during heat treatment, reducing Ag+ into silver colloids. 相似文献
79.
In order to eliminate the errors of the TG method with a static layer, and to determine the influence of the heating rate, the composition of the carrier gas and the particle size of the solids, a method of thermal gas evolution from a fluidized bed (FTGE) with continuous and linear increase of temperature was worked out and the thermal decomposition of diammonium hydrogen phosphate was followed. This method gives reproducible results and makes possible the determination of the apparent activation energies and kinetic parameters.
Some parts presented at the IIIrd Analytical Conference, Budapest, 1970 相似文献
Zusammenfassung Um die Fehler der TG Methode unter fixierten Verhältnissen zu eliminieren, den Einfluß der Temperaturerhöhung, der Zusammensetzung des Trägergases und des Ausmaßes der Festkörper zu klären, wurde eine thermogasanalytische Methode im fluidisierten Bett (FTGE) mit kontinuierlichem und linearem Temperaturanstieg entwickelt und die thermische Zersetzung des Diammonium-biphosphates verfolgt. Man erhielt mit dieser Methode reproduzierbare Ergebnisse. Sie ist zur Bestimmung der scheinbaren Aktivierungsenergien und kinetischer Parameter geeignet.
Résumé Dans le but d'éliminer les erreurs des procédés thermogravimétriques avec couches fixes, et de mettre en évidence l'influence de la vitesse d'échauffement de la composition du gaz porteur et de la dimension des solides, on a développé une méthode d'analyse des gaz dégagés, avec lit fluidifié et élévation de la température continue et linéaire. On a suivi ainsi la décomposition thermique de (NH4)2HPO4. Cette méthode donne des résultats reproductibles et rend possible la détermination des énergies d'activation apparentes et des paramètres cinétiques.
, , . . , .
Some parts presented at the IIIrd Analytical Conference, Budapest, 1970 相似文献
80.
Reaction of trimethylsilyl-protected cytosine with methyl iodide afforded N1-methylated product. Subsequent treatment with ethanol resulted in cleavage of the protection group forming [(MeCyt)2H]I (4). Identity of was confirmed by microanalysis, mass spectrometry, 1H and 13C NMR spectroscopy and by single-crystal X-ray diffraction analysis. Crystals of consist of dimeric [(MeCyt)2H]+ cations and I- anions. These ions are arranged in the crystal such that there is a strong base stacking (mean stacking distance 3,467 angstroms) and, furthermore, pi interactions between I- and cytosine rings (mean distance 3,737 angstroms). The dimeric [(MeCyt)2H]+ cations are centrosymmetric having three strong hydrogen bonds, namely two terminal N4-H...O' ones (N4...O' 2.815(4) angstroms) and a central N3-H...N3' (N3...N3' 2.813(4) angstroms) one. Quantum chemical calculations on the DFT level of theory show that the gas phase structure of the dimeric cation exhibits two different terminal N-HO hydrogen bonds, a stronger (N4...O' 2.722 angstroms) and a weaker one (N4'...O 2.960 angstroms). The central N3-HN3[prime or minute] hydrogen bond (N3...N3' 2.852 angstroms) was characterized to have an unsymmetrically located proton and a typical double minimum potential with a very low activation barrier. The interaction energy between [(MeCyt)H]+ and MeCyt yielding [(MeCyt)2H]+ was calculated to be -42.4 kcal mol(-1)(ZPE and BSSE corrected). Comparison with the interaction energy (calculated on the same level of the theory) between cytosine and guanine yielding the triply hydrogen-bonded Watson-Crick dimer (-24.2 kcal mol(-1)) revealed a much higher stability of the hydrogen bonds in [(MeCyt)2H]+. 相似文献