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101.
102.
Jan Almlf Edwin Haselbach Felicjan Jachimowicz Jozef Kowalewski 《Helvetica chimica acta》1975,58(8):2403-2409
The electrostatic potential (EP.) for aceheptylene (I) is calculated using ab-initio wavefunctions. In addition, the EP. around I is approximated by a monopole expression, using wavefunctions from various semiempirical procedures as a basis. It is found that the previously noted discrepancy between the thoretical prediction of differential nuclophilicity of the individual unsaturated C-atoms in 3,5,8,10-tetramethyl-aceheptylene(II) and the experimental results of protonation is removed, if instead of local atomic charges, the EP. around II, approximated by that of I is considered. 相似文献
103.
104.
105.
13C nuclear spin—lattice relaxation times of 1-methylnaphthalene and 2H nuclear spin—lattice relaxation times of the perdeuterated species, both in deuterochloroform solutions, were measured at several different temperatures. The effects of isotopic substitution on the effective correlation times are discussed. The Woessner approach to extracting the internal jump rates of the CH3 and CD3 groups from these relaxation times was used. Activation energies for the internal motions were calculated by fitting the temperature dependent jump rates to an Arrhenius type expression. The differences between the activation energies of the two isotopic species are discussed. 相似文献
106.
Both alkane- and arene-sulfinates undergo racemization and oxygen exchange reaction with trich-loroacetic anhydride. The rate of racemization of (?)menthyl (?)p-toluenesulfinate was found to be twice that of oxygen exchange, suggesting the reaction involves a Walden inversion. When reaction was carried out in benzene, the rate of racemization was found to be first order with respect to both sulfinic ester and trichloroacetic anhydride. The substituent effect is large (p = ?1.53) suggesting that the initial acylation is the rate-determining step. The rate of racemization was found to be retarded by the addition of perhaloacetic acid while very small catalytic effect of mercuric chloride was observed. 相似文献
107.
108.
109.
J. Šubrt F. Hanousek V. Zapletal J. Lipka M. Hucl 《Journal of Thermal Analysis and Calorimetry》1981,20(1):61-69
The thermal decomposition of synthetic lepidocrocite,γ-FeOOH, was studied using DTA, infrared and Mössbauer spectroscopy and X-ray diffraction, and the dependence of the phase composition of the dehydration products on the method of preparing the initialγ-FeOOH was described. The results demonstrated thatγ-Fe2O3 formed by dehydration ofγ-FeOOH consists of very small particles with a broad size distribution and that, depending on the method of preparation, the initialγ-FeOOH can contain a large amount of amorphous ferric hydroxide. A preparation method yieldingγ -FeOOH which is not contaminated with other ferric oxide-hydroxides is recommended. 相似文献
110.
The ability of various approximate coupled cluster (CC) methods to provide accurate first-order one-electron properties calculated as expectation values is theoretically analysed and computationally examined for BH and CO. For actual calculations the infinite number of terms of the expectation value expansion (O=¦exp (T
+)O exp (T)¦c) was truncated so that T
1
T
2, T
3, and (1/2) T
2T2 clusters were retained on both sides of O. The role of individual clusters is carefully discussed. Inclusion of T
1, is unavoidable, but if triples are essential in the energy evaluation, they may play an even more important role in the property expansion, as shown in the case of CO. It is shown that the CC wave function, which is exact to second order, effectively satisfies the Hellmann-Feynman theorem. 相似文献