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131.
132.
The conformational analysis for a molecule is often performed by assuming that the total conformational energy is a function of two dihedral angles. The resulting conformational energy map is sometimes not easy to interpret because what counts is not energy differences but rather the probability distribution map at a given temperature. In the present article, an algorithm to calculate such a map is given. An example concerning N-substituted amino sugars shows how the conformational probability map may be interpreted. In addition, a similarity index is proposed to get a measure of similarity of the conformational properties of two molecules. The index is based upon the analysis of the conformational probability maps for both molecules. © 1993 John Wiley & Sons, Inc. 相似文献
133.
Site-selective and narrowed luminescence and excitation spectra in the region of the (2)E <-- (4)A 2 transitions are reported for single crystals of Al(acac) 3/Cr(III) and Al(3-Br-acac) 3/Cr(III) (where acac is acetylacetonate). The R 2 line is pronounced in the brominated system and displays a comparable oscillator strength as the R 1 line. The (2)E splitting is found to be 138 cm (-1), and the (4)A 2 ground-state splitting is 1.39 cm (-1). However, in the case of the Al(acac) 3/Cr(III) system the R 2 line is not a distinct feature. We propose that vibronic coupling via a second-order Jahn-Teller effect leads to a redistribution of R 2 intensity over several vibrational sidelines. An upper limit for the R 1 line width Gamma h = 15 MHz is deduced for the Al(acac) 3/Cr(III) 1% system at 1.5 K. This line width is limited by direct and indirect electron-spinelectron-spin interactions. Accurate zero-field splittings (1.20, 1.19, 1.17 cm (-1)) for the three sites in Al(acac) 3/Cr(III) are determined and compared with previously published electron paramagnetic resonance (EPR) data. 相似文献
134.
Jerzykiewicz LB Utko J Duczmal M Sobota P 《Dalton transactions (Cambridge, England : 2003)》2007,(8):825-826
We describe here a novel, simple, efficient self-assembly method for the in situ generation of [Mn4Cl4(micro-OCH2CH2OMe)4(EtOH)4] and [Mn4(micro-Cl)Cl3(micro-OCH2CH2OMe)4(HOCH2CH2OMe)3]2 cubane-type compounds which react readily with calcium species to form cluster [Mn4Ca2Cl4(micro-OCH2CH2OMe)8], the calcium atoms attached to the Mn4 unit of flatten out the cubane inducing significant conformational changes. 相似文献
135.
Lucjan Chmielarz Małgorzata Rutkowska Piotr Kuśtrowski Marek Drozdek Zofia Piwowarska Barbara Dudek Roman Dziembaj Marek Michalik 《Journal of Thermal Analysis and Calorimetry》2011,105(1):161-170
Hydrotalcite-like materials containing apart from magnesium and aluminum also copper, cobalt, nickel, and iron were prepared
by a co-precipitation method. Thermal transformations of hydrotalcite-like materials were studied by thermal analysis methods
as well as XRD, UV–vis–DRS, and XPS measurements of the samples calcined at various temperatures (600, 700, and 800 °C). Calcined
hydrotalcites, especially those containing cobalt and copper, were found to be active and selective catalysts of N2O decomposition. It was shown that an increase in the calcination temperature significantly activated the Co-containing catalysts.
Promotion of the samples with potassium resulted in activation of the hydrotalcite-based catalysts. 相似文献
136.
Lucjan Achremowicz 《合成通讯》2013,43(9):1681-1684
A study of some parameters which influence the oxidation of 2-and 4-methylquinolines with selenium dioxide (or selenious acid) in dioxane has allowed to correct some erroneous opinions of this method and to elaborate a general, simple, fast, and cheap procedure of oxidation of methylquinolines having a methyl group in the position 2 or 4. 相似文献
137.
138.
139.
Lucjan Chmielarz Barbara Gil Zofia Piwowarska Marek Michalik 《Journal of solid state chemistry》2009,182(5):1094-113
Porous clay heterostructures (PCHs) were synthesized using natural montmorillonite as a raw material. Apart from pure silica pillars also silica-titania pillars were intercalated into the interlayer space of the parent clay. The detailed studies of the calcination process of the as-prepared PCH samples as well as thermal stability of the pillared structure of these materials were performed. The pillared structure of PCHs intercalated with both silica and silica-titania clusters was found to be thermally stable up to temperatures exceeding 600 °C. It was found that titanium incorporated into the silica pillars was present mainly in the form of separated tetracoordinated cations. For the samples with the higher Ti loading also small contribution of titanium in the form of the polymeric oxide species was detected. Titanium incorporated into the PCH materials significantly increased their surface acidity forming mainly Brønsted acid sites. 相似文献
140.
Janas Z Nerkowski T Kober E Jerzykiewicz LB Lis T 《Dalton transactions (Cambridge, England : 2003)》2012,41(2):442-447
The diaminebis(aryloxido) ligand precursors H(2)L(1) and H(2)L(2) [H(2)L(1) = Me(2)NCH(2)CH(2)N(CH(2)-4-CMe(2)CH(2)CMe(3)-C(6)H(3)OH)(2); H(2)L(2) = Me(2)NCH(2)CH(2)N(CH(2)-4-Me-C(6)H(3)OH)(2)] were synthesized by a straightforward single-step Mannich condensation. Their reactions with 2 molar equivalents of MeLi in thf afforded [Li(4)(μ-L-κ(4)O,N,N,O)(2)(thf)(2)] (1a, L(1); 1b, L(2)) and unexpectedly small amounts (~9%) of [Li(6)(μ-L-κ(4)O,N,N,O)(2)(μ(3)-Cl)(2)(thf)(4)]·thf (2a·thf; L(1); 2b·thf, L(2)). Stoichiometric reactions of LiCl, MeLi and ligand precursors H(2)L led to the formation of 2a and 2b in high yield (~80%). All compounds were characterized by chemical and physical techniques including X-ray crystallography for H(2)L(1), H(2)L(2), 1b, 2a and 2b. 相似文献