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991.
T. N. Srivastava A. K. S. Chauhan Miss Manjula Agarwal 《Transition Metal Chemistry》1978,3(1):378-379
Summary Binuclear complexes of phenyltin(IV) chlorides with transition metal chelates of tetradentate Schiff bases derived from acetylacetone, benzoylacetone oro-hydroxyacetophenone and ethylenediamine or propylenediamine, of the general formula PhnSnCl4-nML (where n = 1 or 2, M = Ni11 or Cu11 and L2–= the Schiff base dianion), have been synthesised and characterized through elemental analysis, conductance and i.r. spectroscopic data. The coordination of metal chelates to tin involves two triply bonded oxygen atoms giving rise to an octahedral environment around SnIV. The molar conductance of the complexes in nitrobenzene shows the presence of the uncoordinated ML and phenyltin(IV) chloride moieties in solution.Author to whom all correspondence should be directed. 相似文献
992.
The metal chelates of V(IV), Mo(VI) and W(VI) formed with asparagine and glutamine have been studied potentiometrically. Stepwise stability constants in O.1M sodium perchlorate at 25 degrees C are reported as follows. Asparagine chelates--log K(1)K(2) 14.50 and log K(3) 4.04 for V, log K(1) 8.06, log K(2) 7.29 and log K(3) 3.45 for Mo, and log K(1) 5.84, log K(2) 5.11 and log K(3) 3.30 for W. Glutamine chelates--log K(1)K(2) 14.45, and log K(3) 4.07 for V, log K(1) 7.90, log K(2) 6.93, and log K(3) 3.35 for Mo, and log K(1) 5.76, log K(2) 5.09 and log K(3) 3.20 for W. 相似文献
993.
Summary A direct complexometric titration of iron(III) with EDTA using o- and p-cresotic acids indicators is given. The colour change at the end point is from blue-violet to light yellow or colourless [at low concentrations of iron(III)]. The optimum range of pH and temperature for carrying out the titrations is 1.99 to 4.2 and 35° to 55°C and 1.42 to 4.4 and 30° to 60° C, respectively. Iron(III) may easily and accurately be estimated in macro- and micro-gram quantities with the help of these metal indicators. Be, Mg, Ca, Sr, Ba, Cd, UO2 and Mn are without any interference in the estimation. Back titration procedures for determination of zirconium and thorium with iron(III) and o- and p-cresotic acids are carried out.Part V: See Z. analyt. Chem. 173, 196 (1960). 相似文献
994.
The paper describes the synthesis and characterization of comb polymers by a two-step chemo-enzymatic process. In the first step macromonomers bearing unsaturation at the chain end were prepared by lipase catalyzed ring-opening polymerization (ROP) of ε-caprolactone (CL) and 1,5-dioxepane-2-one (DXO). The ROP was carried out in bulk at 60 °C under anhydrous conditions using 2-hydroxyethyl methacrylate (HEMA) as the initiator. The DP of the macromonomers was controlled by regulating the monomer: HEMA molar feed concentration. The macromonomers were then homo- or co-polymerized in the second step with alkyl methacrylate monomers (methyl methacrylate or HEMA) using AIBN initiated free radical polymerization. Characterization of the polymers was done by 1H NMR, SEC and DSC techniques. 相似文献
995.
Seema Tripathi A. K. Srivastava 《Journal of polymer science. Part A, Polymer chemistry》2004,42(9):2060-2065
Triphenylbismuthonium 1,2,3,4‐tetraphenylcyclopentadienylide in 1,4‐dioxan initiated radical polymerization of methyl acrylate to ~30% conversion without gelation because of autoacceleration. The polymer had a viscosity‐average molecular weight of 200,000. The kinetic expression was Rpα[I]0.3[M]1.16, that is, the system followed nonideal kinetics because of primary radical termination and degradative chain‐transfer reactions. The values of kkt and the energy of activation were computed as 3.12 × 10?5 Lmol?1s?1 and 28 kJ/mol, respectively. The ylide dissociated to form a phenyl radical, which brought about polymerization of methyl acrylate. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2060–2065, 2004 相似文献
996.
Hong-Jun Wang William G. Earley Robert M. Lewis Rajiv R. Srivastava Andrew J. Zych David M. Jenkins David J. Fairfax 《Tetrahedron letters》2007,48(17):3043-3046
A highly efficient one-pot, two-step microwave procedure has been developed for the synthesis of 4-substituted 1-heteroarylpiperazines. Microwave heating of heteroaryl chlorides with 1,4-diazabicyclo[2.2.2]octane (DABCO) at 160 °C for 15 min yielded 1-heteroaryl-4-(2-chloroethyl)piperazines, which could be further reacted with various nucleophiles, again under microwave irradiation conditions, to give an array of 4-substituted 1-heteroarylpiperazines in good to excellent yields. 相似文献
997.
The complex formation of lead with Bromopyragallol Red has been studied spectrophotometrically in an attempt to establish composition, stability, thermodynamic parameters and optimum condition for determining small amounts of lead. The blue complex of lead had λmax at 630 nm (against a reagent blank). The composition as determined by different methods is 1:1 at pH 5.5±0.1. The mean value of log K, free energy (ΔG), the heat content (ΔH) and entropy change (ΔS) of the complex are found to be 6.28, ?10.46 kcal/mole and 6.31 e. u. respectively at 25°C. The molecular extinction coefficient and Sendall's sensitivity is 5000 and 0.0140 μg of lead/cm2. The effect of diverse ions was examined with eighteen cations and ten anions, in the determination of lead. 相似文献
998.
999.
Electronic, excitation energies, charge distributions and geometries of pyrazine in the lowest excited singlet π*←π and π*←n states have been studied by the VE—PPP, CNDO/2 and CNDO/s-CI molecular orbital methods. Study of the change of geometry in the π*←n excitation requires localization of the density matrices in the ground and excited states, and with the help of these σ-bond orders are defined. Charge distributions and bond orders in the lowest excited singlet π*←π and π*←n states are compared. Whereas in the lowest singlet π*←π excitation the pyrazine ring expands uniformly, in the case of the π*←n excitation C-C bonds contract whereas C-N bonds elongate. The predictions of theory are in agreement with experimental results, showing that the method used can be employed to obtain reliably the trends of geometry changes following a π*←π excitation of a molecule before a more complete theoretical or experimental study is performed. 相似文献
1000.
Grover RK Roy AD Roy R Joshi SK Srivastava V Arora SK 《Magnetic resonance in chemistry : MRC》2005,43(12):1072-1076
Complete 1H and 13C spectral assignments are reported for six saponins from the pericarp of Sapindus trifoliatus (Hindi name: Reetha) collected from Madhya Pradesh and Maharashtra, India, using only 1D and 2D NMR methods. The structures of the compounds were elucidated as hederagenin 3-O-(3-O-acetyl-beta-D-xylopyranosyl)-(1-3)-alpha-L-rhamnopyranosyl-(1-2)-alpha-L-ara-binopyranoside, hederagenin 3-O-(4-O-acetyl-beta-D-xylop-yranosyl)-(1-3)-alpha-L-rhamnopyranosyl-(1-2)-alpha-L-arabinop-yranoside, hederagenin 3-O-(3,4-O-diacetyl-beta-D-xylopy-ranosyl)-(1-3)-alpha-L-rhamnopyranosyl-(1-2)-alpha-L-arabinopy-ranoside, hederagenin 3-O-(3,4-O-diacetyl-alpha-L-arabinop-yranosyl)-(1-3)-alpha-L-rhamnopyranosyl-(1-2)-alpha-L-arabinop-yranoside, hederagenin 3-O-(beta-D-xylopyranosyl)-(1-3)-alpha-L-rhamnopyranosyl-(1-2)-alpha-L-arabinopyranoside and he-deragenin 3-O-(alpha-L-arabinopyranosyl)-(1-3)-alpha-L-rhamno-pyranosyl-(1-2)-alpha-L-arabinopyranoside. It is concluded that saponins of this complexity approach the limit of structural complexity, which can be solved by NMR alone, precisely and quickly. 相似文献