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91.
Maciej Bujak Jacek Zaleski Victor Prezhdo Boris Uspenskiy 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(2):o76-o77
The title molecule, C11H12O3, is almost planar, with an average deviation of the C and O atoms from the least‐squares plane of 0.146 (4) Å. The geometry about the C=C bond is trans. The phenyl ring and –COOCH3 group are twisted with respect to the double bond by 9.3 (3) and 5.6 (5)°, respectively. The endocyclic angle at the junction of the propenoate group and the phenyl ring is decreased from 120° by 2.6 (2)°, whereas two neighbouring angles around the ring are increased by 2.3 (2) and 0.9 (2)°. This is probably associated with the charge‐transfer interaction of the phenyl ring and –COOCH3 group through the C=C double bond. The molecules are joined together through C—H?O hydrogen bonds between the methoxy and ester groups to form characteristic zigzag chains extended along the c axis. 相似文献
92.
Dabkowska I Rak J Gutowski M Nilles JM Stokes ST Bowen KH 《The Journal of chemical physics》2004,120(13):6064-6071
The photoelectron spectrum of the uracil-alanine anionic complex (UA)(-) has been recorded with 2.540 eV photons. This spectrum reveals a broad feature with a maximum between 1.6 and 2.1 eV. The vertical electron detachment energy is too large to be attributed to an (UA)(-) anionic complex in which an intact uracil anion is solvated by alanine, or vice versa. The neutral and anionic complexes of uracil and alanine were studied at the B3LYP and second-order M?ller-Plesset level of theory with 6-31++G(*) (*) basis sets. The neutral complexes form cyclic hydrogen bonds and the three most stable neutral complexes are bound by 0.72, 0.61, and 0.57 eV. The electron hole in complexes of uracil with alanine is localized on uracil, but the formation of a complex with alanine strongly modulates the vertical ionization energy of uracil. The theoretical results indicate that the excess electron in (UA)(-) occupies a pi(*) orbital localized on uracil. The excess electron attachment to the complex can induce a barrier-free proton transfer (BFPT) from the carboxylic group of alanine to the O8 atom of uracil. As a result, the four most stable structures of the uracil-alanine anionic complex can be characterized as a neutral radical of hydrogenated uracil solvated by a deprotonated alanine. Our current results for the anionic complex of uracil with alanine are similar to our previous results for the anion of uracil with glycine, and together they indicate that the BFPT process is not very sensitive to the nature of the amino acid's hydrophobic residual group. The BFPT to the O8 atom of uracil may be relevant to the damage suffered by nucleic acid bases due to exposure to low energy electrons. 相似文献
93.
Wojciech Duczmal Beata Maciejewska Elżbieta Śliwińska Bogdan Marciniec 《Transition Metal Chemistry》1995,20(2):162-165
Summary Trisubstituted silanes, HSiR3–n
X
n
(R = Me, Et, Pr or Bu; X = Cl, OEt or Ph; and n = 0–3) readily undergo oxidative addition to complex [RhCl(cod)PPh3] (where cod = cycloocta-1,5-diene).The quantitative correlation between rate constants, k
1, of the reaction, followed spectrophotometrically at 20 °C in benzene solutions, and the structure of tri-substituted silanes represented by stereoelectronic parameters , and E of the substituents, was established: logk
1 = a + b + c + dE. The reaction rate is accelerated by electron-withdrawing substituents at silicon and retarded by the bulk and pd donation of nonalkyl substituents.Author to whom all correspondence should be directed. 相似文献
94.
Wagner-Czauderna Elżbieta Boroń-Cegiełkowska Agata Orłowska Elżbieta Kalinowski Marek K. 《Transition Metal Chemistry》2004,29(1):61-65
The visible absorption spectra of CoCl2 in binary mixtures of acetone, dmf, dma and dmso with H2O show the existence of configuration equilibria between tetrahedral (T) and octahedral (O) species. Linear correlations between the values of log K (K = [O]/[T]) and the mole fraction of H2O,
w, have been observed in all the systems under study; their slopes decrease linearly with an increase of the donor number, DN, of the organic component of the mixture. The formation of octahedral species is enthalpy favoured but entropy disfavoured. It was found that both H and S values change linearly with
w and the slopes of these relationships depend clearly on the DN values. 相似文献
95.
Bożena Tutaj Anna Kasprzyk Jan Czapkiewicz 《Journal of inclusion phenomena and macrocyclic chemistry》2003,47(3-4):133-136
A survey of the literature reveals that the spectroscopic displacement method, in which phenolphthalein is used as a competitive chromophore to determine binding constants of β-cyclodextrin with surfactants was successful in the case of homologous hydrocarbon and fluorocarbon anionic surfactants. We show here that this method can be applied also for homologous alkyltrimethylammonium bromides (with alkyl varying from octyl- to hexadecyl) under the condition that the concentration of the cationic surfactant is distinctly lower than the value of itscritical micelle concentration. 相似文献
96.
97.
Jakub Čížek Ivan Procházka Radomír Kužel Rinat K. Islamgaliev 《Monatshefte für Chemie / Chemical Monthly》2002,133(6):873-887
Summary. Ultra-fine grained (UFG) Cu (grain size 80 nm) containing 0.5 wt.% Al2O3 nanoparticles (size 20 nm) was prepared by high pressure torsion (HPT). Positron lifetime spectroscopy was employed to characterize
the microstructure of this material, especially with respect to types and concentration of lattice defects. The evolution
of microstructure with increasing temperature was studied by positron lifetime spectroscopy and X-ray diffraction measurements.
The thermal stability of the Cu + 0.5 wt.% Al2O3 nanocomposite was compared with that of pure UFG Cu prepared by the same technique. The processes taking place during thermal
recovery of the initial nanoscale structure in both studied materials are described.
Received October 5, 2001. Accepted (revised) December 20, 2001 相似文献
98.
Kuśtrowski P Chmielarz L Dziembaj R Cool P Vansant EF 《The journal of physical chemistry. A》2005,109(2):330-336
The novel mesoporous templated silicas (MCM-48, SBA-15, MCF, and MSU) were used as supports for transition metal (Cu, Cr, or Fe) oxides. The catalysts were synthesized using the incipient wetness impregnation, and characterized by low-temperature N2 sorption, DRIFT, photoacoustic IR spectroscopy, UV-vis diffuse reflectance spectroscopy, and temperature-programmed desorption of ammonia. It was shown that the preparation method used results in different distributions and dimensions of the transition metal oxide clusters on the inert support surface. The prepared catalysts were tested in the reaction of oxidative dehydrogenation of ethylbenzene in the presence of nitrous oxide. The iron-containing catalysts showed the highest catalytic activity. The presence of isolated Fe3+ was found to be the most important factor influencing the ethylbenzene conversion. The undesirable effect of the increase in selectivity toward CO2 was observed for the samples with the highest concentrations of acidic surface sites. 相似文献
99.
J. Legendziewicz K. Bukietyńska G. Oczko S. Ernst B. Jeżowska-Trzebiatowska 《Chemical physics letters》1980,73(3):576-581
Absorption spectra of holmium nitrate in MFA and DMF have been measured in the range 8000–42000 cm?1. The τλ parameters were evaluated from the experimental oscillator strengths using the Judd equation. For Ho(NO3)3 in DMF a considerable increase in τ2 was observed, suggesting the existence of inner-sphere species in this system. This suggestion was verified by ultrasonic absorption and conductivity measurements. 相似文献
100.
A fast and simple method for the oxidative iodination of some activated arenes and heteroarenes, either under microwave irradiation or by conventional heating, is reported, using diiodine and ortho-periodic acid as the oxidant. The reactions were carried out in hot 95% ethanol under a reflux condenser. For the microwave assisted reactions, the reaction times were always notably shortened, but the yields were nearly the same as those afforded by the conventional method. 相似文献