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151.
Asymmetric cyclopropanation of alkenes through diazo decomposition mediated by transition metal complexes is a widely investigated catalytic reaction to obtain cyclopropanes where high enantioselectivity is achieved by optimizing metal–ligand combination. Instead of a chronological listing of developments, this review illustrates the existing literature data according to the structural types of ligands in catalytic complexes and attempts to correlate substrate structure and selectivity with ligand design. 相似文献
152.
S. Bose A. Goswami K. S. Chaudhuri 《The Journal of the Operational Research Society》1995,46(6):771-782
An economic order quantity (EOQ) inventory model for deteriorating goods is developed with a linear, positive trend in demand allowing inventory shortages and backlogging. The effects of inflation and the time-value of money are incorporated into the model, considering two separate inflation rates: namely, the internal (company) inflation rate and the external (general economy) inflation rate. It is assumed that the goods in the inventory deteriorate over time at a constant rate θ. The inventory policy is discussed over a finite time-horizon with several reorder points. The results are discussed with a numerical example and a sensitivity analysis of the optimal solution with respect to the parameters of the system is carried out. Several particular cases of the model are discussed in brief. 相似文献
153.
[structure: see text] An artificial macrocyclic fluorescent receptor 1 has been designed and synthesized for the recognition of urea. 1 shows significant fluorescence quenching on complexation with urea and thiourea in chloroform and thus may be used as a synthetic fluorescent molecular sensor for their determination in a nondegradative way. 相似文献
154.
The synthesis, X-ray data, and electronic structures of two manganese(III) 1D polymers ligated by tetrachlorocatechol, [Mn(2)(III)(H(2)L(1))(Cl(4)Cat)(4).2H(2)O](infinity) (1) and [Mn(2)(III)(H(2)L(2))(Cl(4)Cat)(4).2CH(3)CN.2H(2)O](infinity) (2), are reported. The electronic structures of the complexes have been determined by UV-vis-near-IR, IR, electron paramagnetic resonance (EPR), and magnetic susceptibility measurements. Both 1 and 2 are air stable in the solid state and in solution, unlike most of the previously reported o-quinone-chelated transition-metal complexes. Electronic spectroscopy exhibits a strong near-IR band near 1900 nm for both, suggesting the presence of a mixed-valence semiquinone-catecholate oxidation state of the catechol ligands, Mn(2)(III)(Cl(4)Cat)(2)(Cl(4)SQ)(2), together with the pure catecholate forms. The presence of this isomer was further supported by EPR and magnetic susceptibility measurements. The complexes undergo intramolecular electron transfer (valence tautomerism) upon an increase of the temperature involving the equilibrium Mn(2)(III)(Cl(4)Cat)(2)(Cl(4)SQ)(2) <==> Mn(2)(II)(Cl(4)SQ)(4). This phenomenon is reversible and is studied in solution using UV-vis-near-IR spectroscopy. 相似文献
155.
Birendra N. Goswami Jiban C. Sarmah Kataky Jogendra N. Baruah 《Journal of heterocyclic chemistry》1984,21(4):1225-1229
A series of 1-(2,4-dichlorobenzoyl)thiosemicarbazides, s-triazoles and their methyl derivatives have been synthesised by condensation of 2,4-dichlorobenzoyl hydrazine with aryl isothiocyanates. Subsequent ring closure of the substituted thiosemicarbazides yielded the s-triazoles, and reaction with methyl iodide resulted methyl derivatives. All the compounds were subjected to in vitro testing against two gram-positive and two gram-negative bacteria. Antibacterial activity was found to be moderate to good in most of the compounds. 相似文献
156.
Alexandru D. Asandei Yanhui Chen Isaac W. Moran Gobinda Saha 《Journal of organometallic chemistry》2007,692(15):3174-3182
Cp2TiCl is the first example of a single electron transfer (SET) agent that both provides initiating radicals from three different types of functionalities (i.e. radical ring opening of epoxides and reduction of aldehydes and peroxides) and doubles as mediator for the living radical polymerization of styrene (St) by reversibly endcapping the growing polymer chains. An initiator (I) comparison was performed using 1,4-butanediol diglycidyl ether (BDE), benzaldehyde (BA) and benzoyl peroxide (BPO) as models. The investigation of the effect of reaction variables was carried out over a wide range of experimental conditions ([Cp2TiCl2]/[I] = 0.5/1-4/1; [Zn]/[Cp2TiCl2] = 0.5/1-3/1, [St]/[I] = 50/1-400/1 and T = 60-130 °C) to reveal living polymerization features such as a linear dependence of molecular weight on conversion and narrow molecular weight distribution (Mw/Mn) for each initiator class. However, progressively lower polydispersities and larger initiator efficiencies are obtained with increasing the [Cp2TiCl2]/[I] and [Zn]/[Cp2TiCl2] ratios and with decreasing temperature. Accordingly, optimum conditions correspond to [St]/[I]/[Cp2TiCl2]/[Zn] = [50-200]/[1]/[2-3]/[4-6] at 70-90 °C. By contrast to peroxides, aldehydes and the more reactive epoxides provide alcohol end groups useful in block or graft copolymers synthesis. 相似文献
157.
L. Chatterjee G. Das A. Chakravorty R. Goswami S. K. Mondal 《Hyperfine Interactions》1993,82(1-4):143-148
Interesting surprises in some exotic atom kinetics have been reported recently. These involve muonic atom transfer cross sections, nuclear pion capture and theq 1s effect in CF. These can be explained if the exotic atom population contains a contributing fast component. Such fast atoms can be formed by radiative continuum to bound transitions of fast (keV) muons or pions. Cross sections for formation of such fast pionic and muonic atoms and their velocity distributions are reported. The possibility of these processes competing with the thermalisation channels and contributing effectively to the exotic atom population is discussed. 相似文献
158.
[reaction: see text] Scalemic acyclic alpha-(alkoxy)alkyl- and alpha-(N-carbamoyl)alkylcuprates prepared from organostannanes via organolithium reagents react with vinyl iodides, propargyl mesylates, and alpha,beta-enones to afford coupled products with enantioselectivities ranging from 0 to 99% ee depending upon cuprate reagent, substrate structure, solvent, and temperature. In general, lithium cuprates give higher chemical yields and lower enantioselectivities, while the trends are reversed for the corresponding zinc cuprate reagents. 相似文献
159.
160.