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41.
用脉冲回波重叠法测量了钛合金(TC-6)的二阶、三阶弹性常数。实验中发现dμ/dp<0(p<0.17 GPa),dμ/dp>0(p>0.17 GPa)。 相似文献
42.
Thomas C. Amu 《Journal of solution chemistry》1981,10(1):69-78
Interdiffusion coefficient have been measured for 1,1,2,2-tetrabromoethane in 21 organic solvents in order to ascertain the influence of shape, size, viscosity, nature and degree of branching, of the solvent molecules on transport properties. None of the existing correlations for diffusion in binary liquid systems appear to fit all the experimental data. Steric effects due to the solvent molecules are shown to be very important in the interpretation of the diffusion process. 相似文献
43.
The thinning of foam films from aqueous solutions of an ABA triblock copolymer of polyethylene oxide and polypropylene oxide (average molecular weight 14,000 g/mol) is studied experimentally. The dependence of the surface forces on film thickness is obtained by the dynamic method of Scheludko and Exerowa.The total surface force measured in foam films (radius 60–70 m) from 10–5 M (0.014 wt%) polymer solution with 0.1 M NaCl is positive at thicknesses from about 800 down to 460 . The electrostatic repulsion is negligible while the contribution of van der Waals attraction is small (within 15%). Therefore a positive surface force component predominates. Most probably it arises from steric interactions between the hydrophilic polyethylene oxide tails of the polymer. The dynamic method appears to be a suitable technique for exploring the stabilization of foam films from ABA copolymers. 相似文献
44.
I. I. Chuev S. M. Aldoshin O. A. Kozina A. D. Dubonosov E. N. Shepelenko V. A. Bren' V. I. Minkin 《Russian Chemical Bulletin》1992,41(12):2230-2233
X-ray structural analysis was used to determine the molecular and crystal structure of 2-(N-benzyl-N-phenylhydrazinoethylidene)-3-(2H)-benzo[b]thiophenone. The crystals are monoclinic, the space group isC2/c,a=16.022(6),b=11.202(3),c=22.111(4) Å, =81.08(3)°, and andZ=8. It was shown that the ability of hydrazones of a similar class to exhibit photochromic properties is a function of the steric stresses in the molecules and their confirmation.Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences, 142432 Chernogolovka. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2805–2809, December, 1992. 相似文献
45.
Barbara Dogan Hans-Dieter Beckhaus Hermann Birkhofer Christoph Rüchardt 《欧洲无机化学杂志》1990,123(6):1365-1368
Effects of Substituents on the Strength of C - C Bonds, 81. - Heats of Formation and Strain of 1,1,2,2-Tetraethylethylene Glycol Dimethyl Ether and D,L .-1,2-Dimethyl-l,2-diphenylethylene Glycol Dimethyl Ether The heats of combustion of the title compounds 1 and 2 were measured calorimetrically with the result (kcal mol -1, s. d. in parentheses) ΔH°c = − 1880.1 (± 0.6) and − 2373.3 (± 1.4). The heat of vaporisation of 1 ΔHv = 14.3 (± 0.3) and the heat of sublimation of 2 ΔHsub = 27.2 (± 0.5) were derived from their temperature dependance of the vapor pressure. The latter were determined between 30 and 80°C using a flow method. The resulting standard heats of formation ΔH°t(g) = −122.4 (± 0.7) and −43.8 (±1.5) for 1 and 2 correspond to a strain enthalpy (s) of 15.9 and 8.0 kcal mol-1, respectively. The steric strain of the dimethoxyethanes 1 and 2 is about one fourth lower than the strain of the corresponding dimethylethanes 3 and 4 bearing the same substituents. Thus, a methoxy group causes less steric stress than a methyl group. 相似文献
46.
We have demonstrated that the readily available amido-keto compounds 5, with prearranged carbonyl and glycine moieties, under strongly basic conditions easily undergo complete and highly diastereoselective cyclization, affording a generalized and practical access to the conformationally constrained phenylserine derivatives 4. High chemical yields, virtually complete diastereoselectivity combined with the operational convenience of the experimental procedures render this method useful for preparation of these diastereomerically pure derivatives. 相似文献
47.
48.
V. I. Dostovalova L. A. Fedorov Y. Knuutinen E. Kolehmainen J. Paasivirta 《Russian Chemical Bulletin》1994,43(4):566-573
A two-particle system of OY-Cl and OY-Br mixed increments for predicting13C NMR chemical shifts of polyhalogenated polyoxybenzenes has been developed. It has been found that only theortho- and para-interactions of the OY and Hal substituents contribute significantly to the13C chemical shifts and that theortho-effects of the OY located between Ha1 and H and those of the OY located between two Ha1 atoms are different. Additional effects are due to solvating solvents. The increment scheme is predictive over the whole class of compounds under consideration and may be realized on personal computers.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 617–624, April, 1994. 相似文献
49.
Micha? K. Cyrański Paul von Ragué Schleyer Tadeusz M. KrygowskiHaijun Jiao Georg Hohlneicher 《Tetrahedron》2003,59(10):1657-1665
The stability of a set of 105 five-membered π-electron systems (involving aromatic, non-aromatic and anti-aromatic species) was evaluated using six isodesmic reactions of which two belong to the subclass of homodesmotic reactions, which are based on cyclic and acyclic reference systems. We demonstrate that the ‘Resonance Energies’ derived from isodesmotic schemes have obvious flaws and do not correct or cancel other contributions to the energy, such as the changes of hybridization, homoconjugation of heterosubstituted cyclopentadienes, conjugative interactions of CC or CX (X=N or P) with a π or pseudo π orbital at Y (Y=O, S, NH, PH), strain, etc. as effectively as possible. Likewise, ‘aromatic stabilization energies (ASE)’ derived from homodesmotic schemes based on the acyclic reference compounds do not give satisfactory results. We strongly recommend that only cyclic reference compounds should be used for ASE and other aromaticity evaluations. The analysis is based on ab initio optimized geometries at B3LYP/6-311+G∗∗. 相似文献
50.
Thermal
degradation of vinylidene chloride/[4-(t-butoxycarbonyloxy)phenyl]methyl
acrylate copolymers
B. A. Howell D. A. Spears P. B. Smith 《Journal of Thermal Analysis and Calorimetry》2006,85(1):115-117
Vinylidene chloride polymers containing comonomer
units capable of consuming evolved hydrogen chloride to expose good radical-scavenging
sites might be expected to display greater thermal stability than similar
polymers containing simple alkyl acrylates as comonomer. Incorporation of
a comonomer containing the phenyl t-butyl
carbonate moiety into a vinylidene chloride polymer has the potential to afford
a polymer with pendant groups which might interact with hydrogen chloride
to expose phenolic groups. Copolymers of vinylidene chloride with [4-(t-butoxycarbonyloxy)phenyl]methyl acrylate have been
prepared, characterized, and subjected to thermal degradation. The degradation
has been characterized by thermal and spectroscopic techniques. The degradation
of vinylidene chloride/[4-(t-butoxycarbonyloxy)phenyl]methyl
acrylate copolymers is much more facile than the same process for similar
copolymers containing either [4-(isobutoxycarbonyloxy)phenyl]methyl acrylate
or methyl acrylate, a simple alkyl acrylate, as comonomer. During copolymer
degradation, [4-(t-butoxycarbonyloxy) phenylmethyl
acrylate units are apparently converted to acrylic acid units by extensive
fragmentation of the sidechain. Thus, the phenyl t-butyl
carbonate moiety does function as a labile acid-sensitive pendant group but
its decomposition in this instance leads to the generation of a phenoxybenzyl
carboxylate capable of further fragmentation. 相似文献