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991.
In the previous paper(Ⅲ), the following equation of solvent effect in organic chemistry was suggested:
Ei=a﹒Ai(1-Va﹒VAi)+d﹒Di(1-Vd﹒VDi)+E0
Where Ei is a physical or chemical property of the substrate in the solvent i and E0 is that in n-hexane. Ai and Di are constants of electron acception and donation effect of the solvent i respectively. VAi and VDi are constants of electron acception and donation space effect of the solvent i respectively, a and d are the sensitivities of E of the substrate vs the change of Ai and Di. Va and Vd are the constants of electron acception and donation space effect of the substrate respectively. In IR spectra E could be substituted by the wavenumber(ν). Ai and VAi have been established for 18 organic solvents (n-C6H14, n-C7H16, cyclohexane, CCl4, Ph-Me, ClCH:CCl2, Et2O, CHCl3, C6H6, CH2Cl2, ClCH2CH2Cl, Ph-NO2, THF, 1,4-dioxane, Et-NO2. MeCO2Et, Me-NO2, Me-CN).
In this paper Di and VDi have been established for these solvents. The equation also has been tested by the νC-X(X=Cl, Br) of five alkylhalides (t-BuCl, n-C5H11Cl, t-BuBr, Et-Br, EtC(H)BrMe) and νC=O of three carboxyl compounds (t-BuCOMe, Me2CO, MHB) and seven organotin compounds [(Ph2MeSiCH2)3SnO2C-C6H4-X-p(X=H-, CH3-, CH3O-, NO2-, F-. Cl-, I-)].
The relationship (ν=ρ﹒σ+ν0) between νC=O of organotin compounds and Hammett constants(σ) of the substituted groups in different solvents was studied and a relationship betweenρ and Ai, VAi, Di, VDi of the solvents was found. 相似文献
Ei=a﹒Ai(1-Va﹒VAi)+d﹒Di(1-Vd﹒VDi)+E0
Where Ei is a physical or chemical property of the substrate in the solvent i and E0 is that in n-hexane. Ai and Di are constants of electron acception and donation effect of the solvent i respectively. VAi and VDi are constants of electron acception and donation space effect of the solvent i respectively, a and d are the sensitivities of E of the substrate vs the change of Ai and Di. Va and Vd are the constants of electron acception and donation space effect of the substrate respectively. In IR spectra E could be substituted by the wavenumber(ν). Ai and VAi have been established for 18 organic solvents (n-C6H14, n-C7H16, cyclohexane, CCl4, Ph-Me, ClCH:CCl2, Et2O, CHCl3, C6H6, CH2Cl2, ClCH2CH2Cl, Ph-NO2, THF, 1,4-dioxane, Et-NO2. MeCO2Et, Me-NO2, Me-CN).
In this paper Di and VDi have been established for these solvents. The equation also has been tested by the νC-X(X=Cl, Br) of five alkylhalides (t-BuCl, n-C5H11Cl, t-BuBr, Et-Br, EtC(H)BrMe) and νC=O of three carboxyl compounds (t-BuCOMe, Me2CO, MHB) and seven organotin compounds [(Ph2MeSiCH2)3SnO2C-C6H4-X-p(X=H-, CH3-, CH3O-, NO2-, F-. Cl-, I-)].
The relationship (ν=ρ﹒σ+ν0) between νC=O of organotin compounds and Hammett constants(σ) of the substituted groups in different solvents was studied and a relationship betweenρ and Ai, VAi, Di, VDi of the solvents was found. 相似文献
992.
M. Schubert-Zsilavecz D. Gusterhuber W. Likussar G. Färber 《Monatshefte für Chemie / Chemical Monthly》1994,125(6-7):735-742
Summary Regio-, stereo- and siteselectivity of the cycloadditions of trimethylbenzonitrile oxide with 2H-3,4-Dihydro-1,4-benzoxazin-6(8aH)-ones have been investigated. The structures of the obtained products were elucidated by means of homonuclear NOE difference spectroscopy and HMQC and HMBC spectra. The structure of 6-Benzyl-9a-methoxy-3-mesityl-9b-methyl-7,8,9a,9b-tetrahydro-3aH-1,2-oxazolo-[4,5-h]1,4-benzoxazin-4(6H)-on5 was elucidated from a single crystal X-ray structure analysis at ambient temperature: C27H30N2O4, M=446.55g/mol, monoclinic, P21/c,a=10.372 (34) Å,b=11.908 (21) Å,c=20.040 (34) Å, =97.16 (17)°,V=2455.8 (1.9)Å3,Z=4,d
c=1.208g/cm3, =0.08mm–1,R=0.0546.Dedicated to Prof. Ott with best wishes for his 70th birthday 相似文献
993.
The crystalline structure of a new compound Rh(III) of (NH4)2[Rh(NO2)3(NH3)(μ-OH)]2 composition has been determined. The crystallographic characteristics are H16N10O14Rh2: a = 6.3963(2) Å, b = 9.3701(4) Å, c = 13.6646(5) Å, β = 102.266(1)°, V = 800.28(5) Å3, Z = 2, d
calc = 2.432 g/cm3. The distance Rh...Rh in the dimer is 3.200 Å.
Original Russian Text Copyright ? 2006 by S. P. Khranenko, I. A. Baidina, and S. A. Gromilov
__________
Translated from Zhurnal Strukturnoi Khimii, Vol. 47, No. 2, pp. 380–384, March–April, 2006. 相似文献
994.
Carla M. Bossu Edilene C. Ferreira Fernanda S. Chaves Eveline A. Menezes Ana Rita A. Nogueira 《Microchemical Journal》2006,84(1-2):88-92
A flow injection system was proposed to evaluate the transient product of a colorimetric reaction between hydrolysable tannin and potassium iodate (KIO3) solution. The system optimization was accomplished by using statistical methods based on experimental design. Flow rate of KIO3 solution, sample volume, carrier flow rate, and reaction coil were the selected factors for evaluation. On screening step, complete factorial 24 was used and two levels for each selected factor were studied. For the optimization phase, a centered face composite design 22 + star was employed to evaluate sample volume and flow rate of KIO3 solution, which were the factors identified in the screening phase as having more influence on the absorbance signal. After optimization, the proposed system was compared with batch determination. Some characteristics, such as analytical frequency, reagent consumption and chemical residues generation presented better results by the use of the proposed system if compared with batch method. The system presented good repeatability with standard deviation lower than 3%, for n = 10, linearity (R2 = 0.9974) for tannic acid standard, analytical frequency of 15 injections h− 1 and limit of quantification of 24 mg L− 1 of tannic acid. Good results were obtained when the proposed system was applied to hydrolysable tannin determination in Stryphnodendron barbatimão, Eucalyptus citriodora and Phyllanthus niruri, samples of plants commonly used in popular medicine. 相似文献
995.
S. V. Shishkina T. G. Drushlyak L. A. Kutulya N. S. Pivnenko O. V. Shishkin 《Journal of Structural Chemistry》2004,45(5):889-895
X-ray analysis was carried out to study the molecular structure of β-hydroxyketone, which is one of the minor products of selective aldol condensation of (−)-menthone with 4-carbomethoxybenzaldehyde. The cyclohexanone ring of the compound has a practically undistorted chair conformation with an axial orientation of the 1-methyl group and the bulkiest 2-[1′-hydroxy-1′ -(4-carbomethoxyphenyl)]methyl substituent and the equatorial orientation of the isopropyl group in the 4 position. The stereochemical configuration was found to be (1R,2R,4 R, 1′ S), supporting that the compound belongs to the group of (+)-isomenthones; i.e., the starting (-)-menthone undergoes (to a certain extent) epimerization under the reaction conditions used. In crystal, there is intermolecular hydrogen bonding >C=O...HO- (the -O...H- bond length is 2.15 Å). The molecular conformation in hydroxyketone crystals differs from the one which prevails in solutions (according to previous NMR data) and which is characterized by an inverted cyclohexanone ring and intramolecular hydrogen bonding >C=O...HO.Original Russian Text Copyright © 2004 by S. V. Shishkina, T. G. Drushlyak, L. A. Kutulya, N. S. Pivnenko, and O. V. Shishkin__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 933–940, September–October, 2004. 相似文献
996.
Bocian W Kawecki R Bednarek E Sitkowski J Pietrzyk A Williamson MP Hansen PE Kozerski L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(22):5776-5787
The binding constants of camptothecin, topotecan and its lactone ring-opened carboxylate derivative to DNA octamers were measured by UV and NMR spectroscopy. The self-association of topotecan (TPT) was also measured. The carboxylate form of TPT binds in the same way as the lactone, but more weakly. Titration of TPT into d(GCGATCGC)2 shows a preferred location stacked onto the terminal G1 base. However, the intermolecular NOEs cannot be reconciled with a single conformation of the complex, and suggest a model of a limited number of conformations in fast exchange. MD calculations on four pairs of starting structures with TPT stacked onto the G1-C8 base pair in different orientations were therefore performed. The use of selected experimental "docking" restraints yielded ten MD trajectories covering a wide conformational space. From a combination of calculated free energies, NOEs and chemical shifts, some of the structures produced could be eliminated, and it is concluded that the data are consistent with two major families of conformations in fast exchange. One of these is the conformation found in a crystal of a TPT/DNA/topoisomerase I ternary complex [Proc. Natl. Acad. Sci. USA 2002, 99, 15 387-15 392]. 相似文献
997.
998.
Monochrome coloured glass beads of the Merovingians (5th–7th cent. AD) have been examined by different analytical methods. The elemental composition of a large number of mostly unprepared
beads have been measured non-destructively by X-ray fluorescence analysis. After subtracting the content of the colouring
oxides of the glass beads and normalising the residual values to 100% an identical soda-lime-glass matrix was obtained. X-ray
diffraction was used for the identification of the crystalline colouring and opacifying pigments (SnO2, Cu, Cu2O, PbSnO3), and scanning electron microscopy as well as electron probe microanalysis were applied to study the microstructure and the
composition of white, brown, green, orange and yellow coloured glass beads. Oxidised metals, alloys (lead, copper, bronze,
brass and mixtures of them) and iron smelting slag have been identified as raw materials to colour the soda-lime-glass. 相似文献
999.
Vermeiren K 《Journal of chromatography. A》2005,1085(1):66-73
The two-dimensional ion exclusion chromatography/ion chromatography (ICE-IC) approach is considered to be the method of choice for the determination of trace anions in concentrated hydrofluoric acid (48-50%, w/w). In order to achieve lower detection limits, this method was for the first time used with electrolytically generated and purified hydroxide eluents in combination with a low noise electrochemical suppressor. Compared to carbonate based eluents, the achieved gain in peak height sensitivity for chloride, sulfate, nitrate and phosphate is a factor of 6, 7, 16 and 13, respectively. The instrumental detection limits, based on the background noise, are 2, 0.2, 0.4 and 1.4 microg/kg HF 50% (w/w) for the same anions. Their method detection limits, calculated according to SEMI, are all within the 6-10microg/kg HF 50% (w/w) range and thus at least 10 times lower than the current Tier C grade requirements. The chromatographic run time could be shortened with some 10 min by the use of a relatively fast high-capacity hydroxide selective anion exchange column. 相似文献
1000.
Renata Toczy?owska 《Analytica chimica acta》2005,540(1):167-172
Back-side contact Au and Ag microelectrodes were used as transducers to construct planar all-solid-state electrodes suitable for flow-through analysis. The microsensors were based on plasticized PVC potassium-selective membranes containing ion-electron conducting polymer—polypyrrole doped with di(2-ethylhexyl) sulfosuccinate. The proposed technique allowed simple construction of microsensors in one step, by membrane solution casting directly on the surface of the planar metallic transducers. The performance of the microsensors based on Au and Ag transducers were determined and compared with planar sensors based on internal electrolyte immobilized in polyHEMA. The addition of the polypyrrole to the membrane composition did not influence on the selectivity, reproducibility and long-term stability of the microsensors but improved their standard potential stability in time in comparison with coated-wire type sensors. Moreover, all-solid-state microsensors based on Au transducers exhibited better signal stability than Ag based sensors. 相似文献