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排序方式: 共有206条查询结果,搜索用时 31 毫秒
1.
John T. W. Lai Frankie W. Lau Damon Robb Peter Westh Gerda Nielsen Christa Trandum Aase Hvidt Yoshikata Koga 《Journal of solution chemistry》1995,24(1):89-102
The excess partial molar enthalpies, the vapor pressures, and the densities of dimethylsulfoxide (DMSO)–H2O mixtures were measured and the excess partial molar Gibbs energies and the partial molar volumes were calculated for DMSO and for H2O. The values of the excess partial molar Gibbs energies for both DMSO and H2O are negative over the entire composition range. The results for the water-rich region indicated that the presence of DMSO enhances the hydrogen bond network of H2O. Unlike monohydric alcohols, however, the solute-solute interaction is repulsive in terms of the Gibbs energy. This was a result of the fact that the repulsion among solutes in terms of enthalpy surpassed the attraction in terms of entropy. The data in the DMSO-rich region suggest that DMSO molecules form clusters which protect H2O molecules from exposure to the nonpolar alkyl groups of DMSO. 相似文献
2.
Harding WW Tidgewell K Schmidt M Shah K Dersch CM Snyder J Parrish D Deschamps JR Rothman RB Prisinzano TE 《Organic letters》2005,7(14):3017-3020
[reaction: see text] Two new neoclerodane diterpenes, salvinicins A (4) and B (5), were isolated from the dried leaves of Salvia divinorum. The structures of these compounds were elucidated by spectroscopic techniques, including (1)H and (13)C NMR, NOESY, HMQC, and HMBC. The absolute stereochemistry of these compounds was assigned on the basis of single-crystal X-ray crystallographic analysis of salvinicin A (4) and a 3,4-dichlorobenzoate derivative of salvinorin B. 相似文献
3.
The introduction of a 5-trimethylsilyl group on the least hindered face of the diene thebaine was anticipated to favor attack by dienophiles from the alternate face, but only gave rise to a rearrangement product when treated with 3-butene-2-one at 110 °C. Reaction with the more reactive benzoquinone at lower temperature gave rise to a very slow reaction from the same face as the silyl group, indicating that a trimethylsilyl group does not sufficiently hinder this face to achieve reaction at the other face. 相似文献
4.
The reaction between ethyl o-fluorobenzoylacetate and cyclic imino ethers is described. The products, the corresponding 1,2-fused quinolines ( 13a-17a ), were isolated in good yields. In one instance the uncyclized condensation intermediate 18 was isolated and characterized. 相似文献
5.
2-Propynamides react with aryl isocyanates in the presence of triethylamine to give 5-methylene-2,4-imidazolidinediones 5 in good yields. If the propynamide contains a terminal trimethylsilyl group, Z-trimethylsilylidenehydantoin ( 7 ) is produced. 相似文献
6.
Breaux GA Hillman DA Neal CM Benirschke RC Jarrold MF 《Journal of the American Chemical Society》2004,126(28):8628-8629
Calorimetry measurements (using a method based on multicollision induced dissociation) have been performed for unsupported gallium clusters, Gan+ (n = 30-50 and 55). Melting transitions have been identified from spikes in the heat capacities recorded as a function of temperature. There are enormous fluctuations in the melting temperatures and the heats of fusion with cluster size. Clusters with n = 31, 33, 37, and 45-47 are "magic melters" with particularly well-defined melting transitions. There is a strong correlation between the heats of fusion, entropies of fusion, and the stabilities of the clusters. However, these quantities are not strongly correlated with the melting temperatures. 相似文献
7.
P. Gronchi A. Kaddouri P. Centola R. Del Rosso 《Journal of Sol-Gel Science and Technology》2003,26(1-3):843-846
SiO2 and Al2O3 supported Ni catalysts were synthesized in the form of xerogels: the SiO2 based materials were prepared starting from Ni propionate or glycolate salts and reacting them with tetraethoxysilane (TEOS) in propionic acid, Si(ethylene glycolate) or sodium silicate. The Al2O3 supported catalysts were prepared similarly from Ni propionate salts with Al iso-propoxide salts. Narrow metal particles and strong metal support interactions are observed in the sol-gel catalysts. The metal dispersion was higher for Al2O3 based materials than the SiO2 ones and it deeply depends on the Ni precursor for the silica supported Ni. Wet impregnated oxides with similar Ni loading have higher metal surface area than those from sol-gel processing. The influence of surface differences on the catalytic activity of the materials was studied following the CH4 and CO2 reaction in dry reforming conditions by pulse reaction tests. 相似文献
8.
Blum AS Ren T Parish DA Trammell SA Moore MH Kushmerick JG Xu GL Deschamps JR Pollack SK Shashidhar R 《Journal of the American Chemical Society》2005,127(28):10010-10011
Reported in this contribution are the synthesis, characterization, and charge transport properties of wire-like Ru2(ap)4(OPEn), where ap is 2-anilinopyridinate and OPE is -(CCC6H4)nSCH2CH2SiMe3 with n = 1 (1) and 2 (2). Scanning tunneling microscopy (STM) measurements of compound 2 inserted into a SAM of C11 thiol reveal that molecule 2 exhibits (i) the stochastic switching characteristic of wire molecules embedded in insulating SAMs and (ii) higher conductivity than the C11 thiol SAM. More importantly, analysis of the molecular electronic decay constant (beta) exhibits a decrease of at least 15% as compared to purely organic molecular analogues. Hence, the transport characteristics of molecules can be significantly improved for nanoscale electronics through the incorporation of a Ru2 fragment into conjugated backbone. 相似文献
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