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991.
Maria Garrlda Victoria Garcia Matthias Kretschmer Paul S. Pregosin Heinz Ruegger 《Helvetica chimica acta》1981,64(4):1150-1157
The products of the reaction of [RhCl (NBD)]2 (NBD = norbornadiene), with four equivalents tertiary phosphine and two equivalents of tin (II) bromide have been studied by 119Sn- and 31P-NMR. spectroscopy. The solution data suggest that halogen scrambling occurs during the preparation and results in a mixture of complexes containing SnBr3, SnClBr2, and SnCl2Br and SnCl3 ligands, and this is confirmed by independent synthesis of the SnCl3 and SnBr3 complexes. The metalmetal coupling constants, 1J (119Sn, 103Rh), vary from 452 to 580 Hz and are linearly related to: (a) δ(119Sn) in the complexes [Rh (SnClnBr(3-n))NBD (PEtPh2)2] and (b) the sum of the Pauling electronegativities for the halogens on tin. 相似文献
992.
Richard D. Adams Daniel F. Chodosh Nancy M. Golembeski 《Journal of organometallic chemistry》1977,139(1):C39-C43
Reactions of metal carbonyl anions with imidoyl halides provide a convenient route for the preparation of organometallic complexes containing both η1- and η2-iminoacyl ligands. With poorer nucleophiles such as tetracarbonyl cobaltate anion, coupling of imidoyl groupings becomes important. This is illustrated by the molecules Co2(CO)5(P(CH3)2C6H5){(C6H5)CN(C6H5)}2 which has been crystallographically analyzed. 相似文献
993.
Garcia Y Moscovici J Michalowicz A Ksenofontov V Levchenko G Bravic G Chasseau D Gütlich P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(21):4992-5000
[Fe(hyptrz)3](4-chloro-3-nitrophenylsulfonate)22 H2O (1; hyptrz=4-(3-hydroxypropyl)-1,2,4-triazole) has been synthesized and its physical properties have been investigated by several physical techniques including magnetic susceptibility measurements, calorimetry, and M?ssbauer, optical, and EXAFS spectroscopy. Compound 1 exhibits a spin transition below room temperature, together with a very wide thermal hysteresis of about 50 K. This represents the widest hysteresis loop ever observed for an FeII-1,2,4-triazole spin transition material. The cooperativity is discussed on the basis of temperature-dependent EXAFS studies and of the structural features of a CuII analogue. The EXAFS structural model of (1) in both spin states is compared to that obtained for a related material whose spin transition occurs above room temperature. EXAFS spectroscopy suggests that 1,2,4-triazole chain compounds retain a linear character whatever the spin state of the iron(II). 相似文献
994.
A simple procedure for the determination of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), ethyl butyl ether (EBE), tert-amyl methyl ether (TAME), benzene, toluene, ethylbenzene, and xylenes (BTEX) in water using headspace (HS) solid-phase microextraction (HS-SPME) was developed. The analysis was carried out by gas chromatography (GC) equipped with flame ionization detector (FID) and 100% dimethylpolysiloxane fused capillary column. A 2 Plackett-Burman design for screening and a central composite design (CCD) for optimizing the significant variables were applied. Fiber type, extraction temperature, sodium chloride concentration, and headspace volume were the significant variables. A 65 microm poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) SPME fiber, 10 degrees C, 300 g/l, and 20 ml of headspace (in 40 ml vial) were respectively chosen for the best extraction response. An extraction time of 10 min was enough to extract the ethers and BTEX. The relative standard deviation (R.S.D.) for the procedure varied from 2.6 (benzene) to 8.5% (ethylbenzene). The method detection limits (MDLs) found were from 0.02 (toluene, ethylbenzene, and xylenes) to 1.1 microg/l (MTBE). The optimized method was applied to the analysis of the rivers, marinas and fishing harbors surface waters from Gipuzkoa (North Spain). Three sampling were done in 1 year from June 2002 to June 2003. Toluene was the most detected analyte (in 90% of the samples analyzed), with an average concentration of 0.56 microg/l. MTBE was the only dialkyl ether detected (in 15% of the samples) showing two high levels over 400 microg/l that were related to accidental fuel spill. 相似文献
995.
996.
We have used a precision isothermal titration microcalorimeter (ITC) to measure the enthalpy curves for the interaction of a hydrophobically modified polyelectrolyte (D40OCT30) with oppositely charged surfactants (SC(n)S) in aqueous solution. D40OCT30 is a newly synthesized polymer based on dextran having pendant N-(2-hydroxypropyl)-N,N-dimethyl-N-octylammonium chloride groups randomly distributed along the polymer backbone with degree of substitution of 28.1%. The employed anionic surfactants are sodium octyl sulfate (SC(8)S) and sodium tetradecyl sulfate (SC(14)S). Microcalorimetric results along with turbidity and kinematic viscosity measurements demonstrate systematically the thermodynamic characterization of the interaction of D40OCT30/SC(n)S. A three-dimensional diagram with the derived phase boundaries is drawn to describe the effect of the alkyl chain length of surfactant and of the ratio between surfactant and pendant groups on the interaction. A more complete picture of the interaction mechanism for D40OCT30/SC(n)S systems is proposed here. 相似文献
997.
J. M. Garcia de la vega E. San fabian 《International journal of quantum chemistry》1994,52(4):947-956
We have studied symmetry breaking in three open-shell systems: CF (D2d and C2v) and CF (D3h) molecular ions. These different Hartree–Fock solutions are employed as starting points to calculate the correlation energy of these ions with perturbative, configuration interaction, and density functional methods. When symmetry-broken or symmetry-adapted wave functions are used, the correlation energy obtained with each method changes the order of stability of CF for a determined symmetry. Density functional methods produce higher correlation energies although they do not alter the order of stability of Hartree–Fock calculations. The behavior of correlation energy with different methods and the characteristics of the symmetry of wave functions are compared. A study of appearance energies for three different channels of the decomposition reaction of ionized carbon tetrafluoride are considered by using different methods with symmetry-broken or symmetry-adapted wave functions to calculate correlation energies. © 1994 John Wiley & Sons, Inc. 相似文献
998.
The relationship between the calculated energy of the HOMO-LUMO gap, where (epsilonLUMO - epsilonHOMO)/2 is defined as DeltaHL, and of the longest wavelength transition in the UV-visible spectrum, DeltaE, was examined for a series of aromatic and antiaromatic cations and dications. TD-DFT calculations accurately modeled the energies of a series of dications including fluorenylidene dications whose UV-visible spectra are reported, as well as the energies of a series of aromatic and antiaromatic monocations whose spectra were previously reported. There is a linear correlation of the energy of the longest wavelength transition, DeltaEcalc, with DeltaHL. There is no linear relationship between DeltaEcalc and the sum of the NICS values, but there is a linear relationship between DeltaEcalc multiplied by the number of atoms in the conjugated system, DeltaEcalcT, and the sum of the NICS values. There is also an approximate linear relationship between the average 1H NMR shift and the sum of the NICS values. These relationships give further support to the suggestion that the magnetic and energetic criteria of aromaticity and antiaromaticity are related. Furthermore, the data suggest that species that have DeltaEcalcT < 20 are antiaromatic whereas those with DeltaEcalcT > 30 are aromatic. 相似文献
999.
The enzyme-catalysed reduction of nitrate was studied utilising Aspergillus niger nitrate reductase (NR) and phenosafranin in solution as the enzyme regenerator, working at lower potentials than that of the more common methyl viologen mediator. Cyclic voltammograms when enzyme, phenosafranin and substrate were together put in evidence the enzyme-catalysed reduction of nitrate, although with a relatively slow kinetics. From slope values not dependent on mediator concentration, the apparent Michaelis-Menten constant was evaluated. Analytical parameters for the enzyme-modified electrode in the presence of phenosafranin for the determination of nitrate content in water were assessed, including a recovery assay for nitrate added to a river water sample. The stability of the electrode was checked. 相似文献
1000.
A method for the regiospecific synthesis of 3-substituted 2-aroylpyrroles is described. These pyrroles, which are structurally related to the naturally occurring antibiotic pyoluteorin, are prepared by a Friedel-Crafts aroylation of 4-substituted pyrrole-3-carboxylic acid esters with 2,6-dimethoxybenzoyl chloride. The carboalkoxy group is then removed by hydrolysis and decarboxylation to produce isomerically pure 3-substituted-2-(2′,6′-dimethoxybenzoyl)pyrroles ( 5 and 13 ). Conversion of these pyrroles into pyoluteorin-like compounds led to some unexpected products which arise from facile cleavage of the dihydroxybenzoyl portion of the molecules during chlorination. 相似文献