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1.
From flash photolysis data of benzil and 2,2′-dichlorobenzil, the role of conformeric triplets in the formation of hydrogen
adduct radicals has been discussed. The planar relaxed triplet absorbing at 470 nm is less efficient in forming a hydrogen
adduct radical as compared to its puckered conformeric partner. Among the hydrogen donors, triethyl amine and isopropanol,
the former is more efficient in converting puckered triplets and less efficient in the case of planar conformers. Absorptions
of radicals and radical anions of 2,2′-dichlorobenzil appear at 355 nm and 460 nm respectively. These are blue-shifted as
compared to those of the parent compound benzil appearing at 370 nm and 540 nm, respectively. This blue-shift has been discussed
in terms of steric hindrance due to ortho-substitution. 相似文献
2.
The first enantiospecific approach to garsubellin A and related phloroglucin natural product nemorosone, of contemporary interest from (−)-α-pinene, has been delineated. Through a series of stereospecific operations, the requisite stereochemistry of the prenyl groups has been secured. Kende cyclization has been employed as the key step to construct the functionalized bicyclo[3.3.1]nonane core. 相似文献
3.
Mukul Biswas Madhusudan Banerjee Mrinal M. Maiti 《Journal of polymer science. Part A, Polymer chemistry》1984,22(9):1997-2004
Copper(II)-exchanged-13X molecular sieves, prepared from four copper(II) salts, namely, sulfate, nitrate, chloride, and acetate, and their activities in the polymerization of N-vinylcarbazole at a fixed copper ion exchange level were studied. From the kinetic characteristics of polymerization it was established that the variation in activities of the Cu-exchanged sieves is due primarily to the difference in the pH of the original salt solution, which is responsible for the varying degree of proton exchange with the zeolite during copper ion exchange. A first-order dependence of the rate of polymerization was observed with respect to H+ ion concentration of the original copper-salt solution. It was further established that the rate of polymerization of exchanged copper ion, at a hypothetical zero proton concentration, is low. A mechanism of polymerization of NVC on copper-exchanged-13X zeolite was suggested on the basis of the results obtained. 相似文献
4.
Silver-palladium nanodispersions in silicate matrices: highly uniform, stable, bimetallic structures
Ag-Pd nanobimetallic colloidal particles are prepared in a single step by a chemical reduction method. Organically modified aminosilicate is used as a supporting matrix as well as a stabilizing agent, to obtain very uniform, well-distributed bimetallic particles. These nanoparticles are found to be stable for several months in both the solid and the liquid phases. The structure of the bimetallic particles has been followed by X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The distribution and the particle size are determined by transmission electron microscope and X-ray diffraction studies. Polymerization and condensation of the support silicate material have been confirmed by Fourier transform infrared spectroscopy. 相似文献
5.
Mukul Biswas Madhusudan Banerjee Mrinal M. Maiti 《Journal of polymer science. Part A, Polymer chemistry》1985,23(10):2631-2646
Kinetics of polymerization of N-vinylcarbazole over Co(II)-13X molecular sieves in toluene have been studied. The rate of polymerization (Rp) has been found to be second order with respect to percent exchange level of Co(II) and also to the NVC concentration at all the reaction temperatures of 40, 50 and 60°C. The rate increases with decreasing pH of the original exchanging salt solution up to a pH of about 3.5, beyond which it falls. The overall activation energy of polymerization has been found to decrease with increase in monomer concentration, exchange level of Co(II), and the hydrogen ion concentration of the original exchange solution. Average degree of polymerization also follows a similar trend. A mechanism of polymerization involving simultaneous propagation on both metal ion Co(II) and proton on a zeolite surface has been suggested. The two propagation routes are characterized by an average activation energy of 10.36 kcal/mol and 5.40 kcal/mol on the metal ion and proton centers, respectively. 相似文献
6.
Arylazoimidazoles (2) are N,N-chelating ligands. The polymerization trend of the azolate system is restricted via N(1)-benzylation. The parent molecules (2), N(1)-benzylated products (3) and palladium complexes (4) were made by standard methods. The ligands (3) and complexes (4) are new. They have been characterized by elemental analysis, i.r., u.v.-vis. and high resolution 1H-n.m.r. spectral data. Redox studies were carried out by cyclic voltammetry. On complexation, azo reduction is shifted anodically. 相似文献
7.
Reaction of Mo(2)Cl(4)(dppm)(2) (dppm = bis(diphenylphosphino)methane) with 6 equiv of [n-Bu(4)N][CN] or [Et(4)N][CN] in dichloromethane yields [n-Bu(4)N](2)[Mo(2)(CN)(6)(dppm)(2)] (1) and [Et(4)N](2)[Mo(2)(CN)(6)(dppm)(2)] (2), respectively. The corresponding one- and two-electron oxidation products [n-Bu(4)N][Mo(2)(CN)(6)(dppm)(2)] (3) and Mo(2)(CN)(6)(dppm)(2) (4)were prepared by reactions of 1 with the oxidant NOBF(4). Single-crystal X-ray structures of 2.2CH(3)CN, 3.2CH(3)CN.2H(2)O, and 4.2CH(3)NO(2) were performed, and the results confirmed that all three complexes contain identical ligand sets with trans dppm ligands bisecting the Mo(2)(mu-CN)(2)(CN)(4) equatorial plane. The binding of the bridging cyanide ligands is affected by the oxidation state of the dimolybdenum core as evidenced by an increase in side-on pi-bonding overlap of the mu-CN in going from 1 to 4. The greater extent of pi-donation into Mo orbitals is accompanied by a lengthening of the Mo-Mo distance (2.736(1) A in Mo(2)(II,II) (2), 2.830(1) A in Mo(2)(II,III) (3), and 2.936(1) A in Mo(2)(III,III) (4)). A computational study of the closed-shell members of this homologous series, [Mo(2)(CN)(6)(dppm)(2)](n)() (n = 2-, 0), indicates that the more pronounced side-on pi-donation evident in the X-ray structure of 4 leads to significant destabilization of the delta orbital and marginal stabilization of the delta() orbitals with respect to nearly degenerate delta and delta orbitals in the parent compound, 2. The loss of delta contributions combined with the reduced orbital overlap due to higher charges on molybdenum centers in oxidized complexes 3 and 4 is responsible for the observed increase in the length of the Mo-Mo bond. 相似文献
8.
Parnajyoti Karmakar Sumon Ray Debabrata Nandi Arup Mandal Subala Mondal Subhasis Mallick Biplab K. Bera Alak K. Ghosh 《Journal of solution chemistry》2013,42(2):441-458
The kinetics of the substitution reactions of [Pt(dach)(H2O)2]2+ and [Pt(en)(H2O)2]2+ (where ‘dach’ and ‘en’ are cis-1,2-diaminocyclohexane and ethylenediamine, respectively) with excess N,N′-diethylthiourea have been studied in aqueous solution by UV–Vis spectrophotometry. The effect of different N–N spectator ligands on the reactivity of platinum(II) complexes was investigated by studying the water lability of the reactant complexes. The kinetic study has been substantiated by product isolation, IR, NMR and ESI-MS spectral analysis and DFT calculations. The reactions follow normal square-planar substitution mainly in an associative way. Rate parameters have been evaluated under different conditions. The substitution rates of the complexes studied can be tuned through the nature of the N–N chelates, which is important in the development of new active compounds for cancer therapy. 相似文献
9.
AgBArF displays remarkable ‘on-water’ activity for catalytic hydration of terminal alkynes although it is ineffective in common organic solvents. Liquid alkynes do not require additive or co-solvent whereas a small amount of ethyl acetate triggers quantitative conversions for solid alkynes. 相似文献
10.
A heterobimetallic supramolecular polymer (polyRuFe) with alternately complexed Ru(II) and Fe(II) is prepared following a stepwise synthetic route through harnessing first the strongly binding metal ion Ru(II) and then the weakly binding metal ion Fe(II). A high yield of product is achieved in each step. The heterometal ions are incorporated into the polymer chain in identical coordination environments formed by two 2,2′:6′,2″-terpyridine moieties. Characterization is accomplished by NMR spectroscopy, MALDI–TOF mass spectrometry, UV–Vis spectroscopy, and cyclic voltammetry. PolyRuFe shows a wide optical window (λ = 311–577 nm) and a broad distinct reversible redox nature of two types, originated from the coupling of the two heterometallic segments into the polymer chain. Such characteristics of polyRuFe suggest its potential for various electrochemical and electro-optical applications. 相似文献