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Coupled Hartree–Fock perturbation theory, within the framework of an accurate calculation, has been employed to visualize the electronic current density vector field induced by an external uniform magnetic field in the acetylene molecule. The current regime in a plane containing the molecular axis is rather different from those usually accounted for, evidencing the presence of a toroidal vortex in the C? H bond. The maps are useful in rationalizing the experimentally observed proton and carbon NMR chemical shifts. 相似文献
54.
The ab initio energies, nuclear and electron repulsions and charge distributions have been calculated using moderately large basis sets as a function of the RC N angle (R NH2, NF2 or PF2). The optimum RC N angles were calculated to be 178.9°, 176.6°, and 175° for NH2CN, NF2CN, and PF2CN, respectively. A rationalization of the differing bends is presented in terms of nuclear-nuclear and electron-electron repulsions. 相似文献
55.
The hydrolysis of p-F, p-Cl, and m-Cl phenyl trifluoracetates was studied in the presence of beta-cyclodextrin (beta-CD). The reactions are inhibited by beta-CD at pH 6 while they are catalyzed in alkaline solution. MM3 calculations reproduce some of the experimental results. The substrates form inclusion complexes with beta-CD which are of similar stability as those of the corresponding acetates; however, the association of the transition state is less favorable in these reactions than in those of the acetates, and consequently less stronger catalysis is observed. 相似文献
56.
Siham El FangourAlexandre Guy Jean-Pierre VidalJean-Claude Rossi Thierry Durand 《Tetrahedron letters》2003,44(10):2105-2108
The first synthesis of the two enantiomers of phytoprostane F1 methyl ester 1 and 2 is described using the syn-anti-syn alcoxy ester 3 as starting material. 相似文献
57.
Yerdos Ongarbayev Ainur Zhambolova Yerbol Tileuberdi Zulkhair Mansurov Cesare Oliviero Rossi Pietro Calandra Bagdat Teltayev 《Molecules (Basel, Switzerland)》2022,27(10)
This paper considers the effect of aging processes on viscoelastic characteristics of vacuum residue oxidation products modified with crumb rubber. Viscoelastic properties were compared to original bitumen raw material-vacuum residue and vacuum residue oxidation products during short-term and long-term aging. The complex shear modulus of the vacuum residue and its oxidation products decreased with an increase in temperature. Short-term aging resulted in increased shear modulus for all samples.The vacuum residue oxidation product modified with crumb rubber had the maximum values of the rutting parameter and fatigue parameter. There was an expansion of the temperature range of plasticity: for the vacuum residue oxidation product with crumb rubber, its value was 67.2 °C. The curves of the black diagram of the modified vacuum residue oxidation product are shifted towards smaller phase angles with the increase in the shear modulus, which indicates the increase in the stiffness and elasticity of the rubber bitumen binders. The vacuum residue oxidation product modified with crumb rubber corresponded to the rubber bitumen binder of the grade RBB 60/90, according to its physical and mechanical indicators. 相似文献
58.
Jos Roberto Berretta Wagner de Rossi Maurício David Martins das Neves Ivan Alves de Almeida Nilson Dias Vieira Junior 《Optics and Lasers in Engineering》2007,45(9):960-966
The technique to weld AISI 304 stainless steel to AISI 420 stainless steel with a pulsed Nd:YAG laser has been investigated. The main objective of this study was to determine the influence of the laser beam position, with respect to the joint, on weld characteristics. Specimens were welded with the laser beam incident on the joint and moved 0.1 and 0.2 mm on either side of the joint. The joints were examined in an optical microscope for cracks, pores and to determine the weld geometry. The microstructure of the weld and the heat affected zones were observed in a scanning electron microscope. An energy dispersive spectrometer, coupled to the scanning electron microscope, was used to determine variations in (weight %) the main chemical elements across the fillet weld. Vickers microhardness testing and tensile testing were carried out to determine the mechanical properties of the weld. The results of the various tests and examinations enabled definition of the best position for the incident laser beam with respect to the joint, for welding together the two stainless steels. 相似文献
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Massimo Curini Francesco Epifano Maria Carla Marcotullio Ornelio Rosati Monia Rossi André Tsadjout 《合成通讯》2013,43(17):3181-3187
Layered zirconium hydrogen phosphonate exchanged with the potassium ion was found to be an efficient heterogeneous catalyst for the hydrolysis of sterically hindered phenolic silyl ethers. 相似文献