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1.
A new approximate method for the determination of the valence bond angles for MX ****
k
-type molecules, based on the maximum overlap principle, is proposed. The valence bond angles are determined from the conditions of maxima of the total bonds strength. The method has been used to calculate the valence angles and the hybrid orbitals for the water, and the ammonia molecule, respectively. The calculated valence bond angles for both molecules are about 2 too high with respect to experimental equilibrium values. Also the best hybrid orbitals using the Golebiewski simplified method were calculated.
Zusammenfassung Eine neue NÄherungsmethode für die Bestimmung der Valenzwinkel für Moleküle vom Typ MX **** k wird vorgeschlagen, die sich auf das Prinzip der maximalen überlappung gründet. Die Valenzwinkel werden aus der Forderung nach einem Maximum der GesamtbindungsstÄrke abgeleitet. Die Methode wird zur Berechnung der Valenzwinkel und der Hybridorbitale von H2O und NH3 angewendet. Die berechneten Valenzwinkel sind für beide Moleküle etwa 2 zu hoch gegenüber den experimentellen Gleichgewichtswerten. Die besten Hybridorbitale werden entsprechend der vereinfachten Methode von Golebiewski berechnet.
Résumé On propose, sur la base du principe du recouvrement maximum, une nouvelle méthode approchée pour la détermination des angles des liaisons de valence des molécules de type MX **** k . Ces angles sont déterminés à partir des conditions de maxima de la «force totale de liaison». La méthode a été utilisée pour calculer les angles de valence et les orbitales hybrides de l'eau et de l'ammoniac. Les valeurs obtenues sont supérieures d'environ 2 aux valeurs expérimentales. Les meilleures orbitales hybrides de ces deux molécules ont été aussi calculées par la méthode simplifiée de Golebiewski.相似文献
2.
Stanislaw Zaręba 《Mikrochimica acta》1993,112(1-4):119-126
METRIAREZ- and -, two new derivatives of 5-mercapto-1,2,4-triazole with - and -resorcylic acids have been synthesized and their physicochemical and chelating properties determined. With metal ions havingp andd electrons they form water-soluble coloured chelates at L M molar ratios of 1 1 with Cu2+ and Pb2+ ( and ), Hg2+ and Zn2+ () and Cd2+, In3+ and Bi3+ () and 2 1 with Fe3+, Fe2+, Co2+ and Ni2+ ( and ) and Zn2+ (). The chelates are non-extractable by organic solvents. The stability constants of these complexes, as well as their spectrophotometric sensitivity and extinction coefficients were determined. Iron and zinc in multivitamin tablets were determined spectrophotometrically using the ligands. 相似文献
3.
Two new glycosides of limocitrin have been isolated from the epigeal part ofHaplophyllum perforatum (M. B.) Kar. et Kir. On the basis of chemical transformations and spectral characteristics the structures of the substances isolated have been established as 7-(6-acetyl--D-glucopyranosyloxy)-3,4,5-trihydroxy-3,8-dimethoxyflavone and 7-[0--L-rhamnopyranosyl-(1 2)--D-glucopyranosyloxy]-3,4,5-trihydroxy-3,8-dimethoxyflavone.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 192–196, March–April, 1985. 相似文献
4.
Irina Karadjova 《Mikrochimica acta》1999,130(3):185-190
Methods are described for the determination of trace and ultra trace amounts of Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb in natural waters, alkali and alkaline earth salts. Separation and preconcentration of trace metals is achieved by a column solid phase extraction procedure using silica gel modified with derivatives of dithiocarbamates — Na-DDTC (sodium diethyldithio-carbamate and HMDTC (ammonium hexamethylene-dithiocarbamate) as column packing material. The influence of the sorbent preparation procedure on the degree of sorption of the trace analytes is examined for different pH values of the sample solution. Isobutylmethyl ketone (IBMK) is proposed as an effective eluent for quantitative elution of retained metal ions. Optimal instrumental parameters for ETAAS determination of preconcentrated elements in organic eluate are presented. Practical application of sorbents in analysis of natural waters and alkali and alkaline earth salts is demonstrated. Proposed preconcentration procedure combined with ETAAS determination of trace analytes allows the determination of 0.04 g l–1 Cd, 0.1 g l–1 Cr, Cu, and Mn and 0.3 g l–1 Co, Fe, Ni and Pb in natural waters and 1.10–7% Cd, 3.10–7% Cr and Mn, 7.10–7% Co, Ni and Pb and 2.10–6% Cu and Fe in alkali and alkaline earth salts. 相似文献
5.
Specific sorption sites for nitrogen, N2, in NaLSX and LiLSX zeolites were investigated using a DRIFT spectroscopic method. Sorption of molecular hydrogen, H2, by NaLSX or LiLSX zeolite at 77 K with DRIFT control of perturbation of sorbed molecules allowed to discriminate two or three different types of specific sorption sites in the respective zeolites. Their H–H stretching frequencies are 4077 and 4081 cm–1 for NaLSX, and 4061, 4084 and 4129 cm–1 for LiLSX. With reference to an independent investigation by methods of both sorption thermodynamics and molecular modeling for N2 sorption on LiLSX, the first two of the corresponding bands were ascribed to H2 sorption on lithium cations, Li+, localized in supercages of the faujasite, FAU, zeolite framework at sites SIII and SIII, while the latter band most likely belongs to H2 sorption on Li+ cations at sites SII, and on hydroxyl groups, OH. Sorption of N2 by Li+ cations at sites SIII and SIII is the strongest, resulting in a decrease of intensity of the corresponding DRIFT bands that stem from subsequent H2 sorption. Nitrogen sorption by Li+ cations at sites SII is much weaker. Sorption of N2 on Na+ cations at sites SIII in NaLSX zeolite is also stronger than by Na+ cations at sites SII. 相似文献
6.
B. Unger H. -W. Meiners H. Toufar F. Scheffler K. -P. Wendlandt 《Reaction Kinetics and Catalysis Letters》1991,43(2):571-575
Computer handling of TPAD data reveals a decreasing strength of Brönsted sites and forced diffusion limitations caused by incorporation of boron at pentasil type zeolite lattice positions.
, , , .相似文献
7.
Françoise Guérin 《Theoretical chemistry accounts》1970,17(2):97-108
Résumé On a calculé les courbes d'énergie potentielle de plusieurs états excités de N2
+, CN et CO+, en utilisant les fonctions d'onde LCAO MO SCF. Les valeurs calculées des constantes spectroscopiques et spin orbite sont en bon accord avec l'expérience. Notre calcul prévoit qu'on ne peut pas observer de transition 2
-A
2
dans CO+, et confirme que l'état supérieur de la transition récemment observée est un état 2 et non 2
.
Potential energy curves have been calculated for several excited states of N2 +, CN and CO+, using LCAO MO SCF functions. Good agreement with experiment has been obtained for spectroscopic and spin orbit constants. From our calculation, 2 -A 2 transition in CO+ is predicted to be non observable, but we confirm that the upper state of the experimentally observed transition is 2 r and not 2 .
Zusammenfassung Für verschiedene angeregte Zustände der iso-elektronischen Moleküle N2 +, CN und CO+ wurden unter Verwendung von LCAO-MO-SCF-Funktionen die Potentialkurven berechnet. Für die spektroskopischen und die Spin-Bahn-Kopplungskonstanten wurde gute Übereinstimmung mit dem experimentellen Befund erreicht. Unseren Berechnungen nach sollte der 2 -A 2 -Übergang in CO+ nicht beobachtbar sein, während die Rechnung bestätigt, daß der obere Zustand des experimentell beobachteten Überganges ein 2 r -Zustand und nicht ein 2 -Zustand ist.相似文献
8.
Measurements of NMR spin-lattice relaxation times T
1
were performed for sorbed H2O and D2O in a sulfonated ion-exchange resin at varying degrees of hydration with alkaline cations as counter ions. From the sorption isotherms at three different temperatures the partial molar enthalpies
and entropies
of sorption show a minimum for all alkaline cations at water concentrations of n 0.8, i.e., there are 0.8 water molecules per –SO
3
–
group. The first water molecules sorbed in the ion-exchange resin matrix are characterized by anisotrtopic rotational diffusion processes with correlation times of the order of 1 50 ns and 2 30 ps, respectively. This indicates that they are located in the electrostatic field between the corresponding ion pair. Although these two correlation times are very similar at a given temperature for all alkaline cations studied in the present investigation, the existence of a second spin-lattice relaxation time for sorbed H2O at n=0.8 indicates that for Cs about 50% of the sorbed water diffuses between locations in the resin. This fraction decreases with ionic radii and with falling temperatures. For Li the amount is less than 20%. 相似文献
9.
Kaizaki Sumio Kita Przemyslaw Wiśniewska Joanna Sakagami Narumi 《Transition Metal Chemistry》1998,23(4):511-515
Three new complex ions, [Cr(NCS)(R-pdtrp)]-, [Cr(R-pdtrp)(NCSHg)]+ and [Cr(edtrp)(NCSHg)]+, that are derivatives of the trans-equatorial isomers of [Cr(R-pdtrp)(H2O)]0 and [Cr(edtrp)(H2O)]0 (edtrp= ethylenediamine-N,N,N-tripropionate, R-pdtrp= R-propane-1,2-diamine-N,N,N-tripropionate) have been obtained and characterized in solution. Rate constants and activation parameters, including, in two cases, volumes of activation, have been determined. Rate retardation for NCS- ligand release has been observed with increasing acidity within the pH 0–2 range. The mechanism of the reactions has been discussed. 相似文献
10.
Remi Chauvin 《Journal of mathematical chemistry》1996,19(2):147-174
Within the prospect of quantifying the geometrical dissimilarity of molecular models on the basis of a thermodynamical formalism, the algebra of stereogenic pairing equilibria is reviewed and applied to molecular geometry: developing Rassat's proposition, an interaction energy of two figures F and F is taken as proportional tod
H
Emphasis>/2
(F, F), whered
H denotes the Hausdorff distance. IfG is a group of rotations in E
n
the geometrical version of the general equation (E) of the chemical algebra defines a distance extensionD
p(F,F) ofd
H(F,F), which is independent of the orientations of F and F, and where the coefficientp is interpreted as the reciprocal of a temperature-like parameter:p 1/T. At K (p = ), no formal entropy contributes to the definition of the uniform distanceD
. At K (p = 0), the discrimination between homo- and hetero-pairing of figures by the harmonic distance Do is averaged over orientation states. Temperature-dependent chirality measuresc
p are derived fromD
p, andc
is analogous to Mislow's chirality measure. If T and oT are normalized enantiomorphic triangles with coincident centroids inE
2,c
p(T) =D
p (T, T) is calculated forp = 0 andp = , and discussed for 0 <p < . Finally, the Hausdorff interaction model is putatively related to energy profiles versus dihedral angle inmeso- anddl-molecules. 相似文献
11.
Sadhan Basu 《Theoretical chemistry accounts》1965,3(2):156-158
Using a free electron model for the -electron system in aromatic hydrocarbons the - electron susceptibility due to Langevin diamagnetism and Van Vleck High frequency para-magnetism (H. F.) have been calculated. The H. F. term has been found to increase rapidly with the ring size.
Zusammenfassung Mit Hilfe eines Modells freier Elektronen für das -Elektronensystem in aromatischen Kohlenwasserstoffen wird der Langevinsche diamagnetische Anteil und der Van Vlecksche paramagnetische Beitrag zur -Elektronensuszeptibilität berechnet. Dabei findet man, daß letzterer mit der Ringgröße schnell wächst.
Résumé Au cadre du modèle de l'électron libre, la susceptibilité -électronique des hydrocarbures benzéniques due au diamagnétisme de Langevin et au paramagnétisme de Van Vleck (H. F.) a été calculée. Le terme H. F. s'agrandit rapidement avec les dimensions de la molécule.相似文献
12.
B. Pateyron M. F. Elchinger G. Delluc P. Fauchais 《Plasma Chemistry and Plasma Processing》1996,16(1):39-57
In most cases the energy dissipated in plasma jets used either,for heating or spraying is varied by changing the are current, the total gas floc+rate, and composition. However, when doing so, conditions are reached where the plasma jet may become supersonic. To predict such conditions or to characterize supersonic plasma jets the knowledge of the sound velocitya is mandatory The goal of this paper is to calculatea versus plasma forming gas composition, temperature, and pressure. Rigorous calculation would imply the knowledge of the chemical reaction kinetics, sound velocity depending strongly on this. Unfortunately such kinetics are generally lolknown for plasma jet floras and the only possibility is to determine the equilibrium sound velocitya calculated through the isentropic coefficient T. This coefficient has been calculated taking into account the dissociation and ionization reactions at equilibrium for temperatures ranging from 300 to 25,000 K and pressures between 0.1 and 1 Mpa for Ar, H2, He, Ar-He, Ar-H2, O2, N2, air, .steam, and methane.a often called the frozen sound velocity, was also calculated using (ratio of specific heats) instead of . 相似文献
13.
Emil B. Milosavljević Ljiljana Solujić John H. Nelson James L. Hendrix 《Mikrochimica acta》1985,87(5-6):353-360
Summary
Simultaneous Determination of Chromium(VI) and Chromium(III) by Flame Atomic Absorption Spectrometry with a Chelating Ion-Exchange Flow Injection System
A simple method is described for the simultaneous determination of chromium(VI) and chromium(III) in a flow injection system comprising chelating ion-exchange and flame atomic absorption spectrometry. Sampling rates for 2001 and 1 ml sample volumes were 120 and 60 h–1 (240 and 120 speciations per hour), respectively. Typical relative standard deviations were 0.52% for Cr(VI) (0.50g ml–1 and 0.67% for Cr(III) (0.10,g ml–1) and the corresponding limits of detection were 85 ng ml–1, and 16 ng ml–1, respectively.On leave from University of Belgrade. 相似文献
14.
Yu. V. Belokopytov Yu. N. Grebennikov G. P. Korneichuk 《Reaction Kinetics and Catalysis Letters》1981,16(4):409-412
Benzene is shown to be adsorbed on the surface of a V2O5-MoO3 catalyst in two forms. The activation energies of benzene desorption for its first and second forms are 50 and 134 kJ/mol, respectively, in the latter case the adsorption proceeding with dissociation.
, - . 50 / –134 /, .相似文献
15.
V. B. Okhotnikov 《Reaction Kinetics and Catalysis Letters》1989,38(2):359-362
It is suggested that besides its traditional application to describe random nucleation, the first-order equation F1 can be used for the diffusion kinetics of gas-solid small particles reactions.
, F1 - - .相似文献
16.
2,3-Dihydroxypyridine loaded (via –N=N–linker) Amberlite XAD-2 (AXAD-2-DHP) was prepared and characterized by elemental analyses, TGA and FT-IR spectra. It (1g packed in a column of 1cm diameter; surface area 135.5m2g–1) was found to be an effective solid phase sorbent for enriching Zn2+, Mn2+, Ni2+, Pb2+, Cd2+, Cu2+, Fe3+ and Co2+ at pH 3.5 to 7.0 using flow rates between 1.0–5.0mLmin–1. For desorption (recovery 97.0–99.8%) of the metal ions, 8 to 10mL of 2.0molL–1 HCl or 1.5molL–1 HNO3 at a flow rate of between 2.0 and 4.0mLmin–1 were found most suitable. The t1/2 (time for 50% sorption) is between 2 and 10min when a 50mL solution (containing a total amount of metal of 2mg) was equilibrated with 0.5g of resin. Sorption of all metal ions except Pb2+ follows the Langmuir model, whereas for Pb the data fits with the Freundlich model. The sorption capacity is between 60.7 (for Cd) and 406.7 (for Cu) µmolg–1. The resin can withstand an acid concentration of 6molL–1 and can be reused for thirty cycles of sorption–desorption. The preconcentration factor varies between 100 and 300. For Cd, Ni and Cu the sorption capacity of 2,3-dihydroxypyridine loaded cellulose is lower than that of the present resin. The tolerance limits of electrolytes, humic acid, complexing agents, Ca2+ and Mg2+ in the enrichment of all metal ions are reported. The limits of detection are 3.88, 5.37, 8.72, 13.88, 4.71, 1.24, 0.59 and 0.30µgL–1 for Zn2+, Mn2+, Ni2+, Pb2+, Cd2+, Cu2+, Fe3+ and Co2+, respectively. The calibration curves for flame AAS determination were linear in the ranges 0.018–1.0, 0.067–5.0, 0.2–5.0, 0.9–20, 0.028–2.0, 0.077–5.0, 0.19–10 and 0.1–3.5µgmL–1, respectively. All the eight metal ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples have been quantitatively enriched with Amberlite XAD-2-DHP and determined by flame atomic absorption spectrometry. 相似文献
17.
E. Reiffenstein H. Nowotny F. Benesovsky 《Monatshefte für Chemie / Chemical Monthly》1966,97(5):1428-1436
Zusammenfassung Der Metall-Metall-Austausch in Komplexcarbiden wird röntgenographisch und magnetochemisch untersucht. Das -Mn-Carbid Mo3Al2C ist bis MoCr2Al2C homogen, die Mischphase weist auf antiferromagnetisches Verhalten hin. Im -Carbid Nb3(Cr, Al)3C besetzen die Cr-Atome zuerst die 16 d) und erst dann die 32e) Lage. Geringe Cr/Al-Substitution führt zu spontaner Magnetisierung (Temperatur des flüssigen Stickstoffs) in den -Phasen Nb3(Cr, Al)3C und Ta3(Cr, Al)3C. Chrom ist der Träger des Magnetismus, während sich der Oktaederverband {Nb6C} oder {Ta6C} ähnlich wie in den einfachen Carbiden verhält.
Mit 5 Abbildungen 相似文献
Complex carbides have been examined with respect to metal-metal substitution by means of X-ray and magnetic measurements. The solid solution Mo3–1Cr0–2Al2C having -Mn-carbide type exhibits antiferromagnetic behavior. Within the -carbide of formula Nb3(Cr, Al)3C the Cr-atoms are filling the 16 d) position first, followed by a filling of the 32e) position. Minor Cr/Al-substitution leads to spontaneous magnetization (at the temperature of liquid nitrogen) for the -carbide phases Nb3(Cr, Al)3C and Ta3(Cr, Al)3C. This is due to the presence of chromium atoms while the octahedral framework {Nb6C} or {Ta6C} behaves similar as is the case in binary carbides.
Mit 5 Abbildungen 相似文献
18.
T. E. Kokina L. A. Glinskaya R. F. Klevtsova S. V. Larionov 《Journal of Structural Chemistry》2002,43(2):312-321
The reaction of Ni{(i-C4H9)2PS2}2 with imidazole and 3,5-dimethylpyrazole in ethanol gave paramagnetic (ef = 3.02 and 3.11 BM) mixed-ligand complex compounds [Ni(Im)2{(i-C4H9)2PS2}2] (I) and [Ni(Pyr){(i-C4H9)2PS2}2] (II). Single crystals were grown and the crystal structures of I and II were determined from X-ray diffraction data (CAD-4 diffractometer, Mo
radiation, 1483
, R = 0.0344 for I and 2630
, R = 0.0486 for II). The crystals are monoclinic with cell dimensions a = 12.845(2), b = 10.250(1), c = 13.431(1) , = 115.89(1)°, V = 1591(1) 3, Z = 2, d
calc = 1.281 g/cm3, space group
(for I); a = 11.152(3), b = 12.483(2), c = 23.389(4) , = 100.78(1)°, V = 3199(2) 3, Z = 4, d
calc = 1.191 g/cm3, space group
(for II). The structures consist of discrete monomer molecules. The coordination polyhedron of the Ni atom is a compressed octahedron NiN2S4 (in I) and a tetragonal pyramid NiNS4 (in II) formed by four S atoms of the two cyclic bidentate ligands i-Bu2
and the N atoms of two monodentate ligands (Im molecules in trans-positions) or the N atom of the monodentate Pyr ligand in complexes I and II, respectively. The character of interaction between molecules I and II and molecular packing modes are considered. The electronic spectra of the complexes are consistent with the symmetry of chromophores found from X-ray data. 相似文献
19.
The ab initio MP2 method is used with the LANL2DZ basis to calculate the mercury chloride ,-complex with two acetylene molecules (1) and various isomeric forms of mercury di()-vinyl chloride -complexes (2): cis-cis (2A), cis-trans (2B), and trans-trans (2C). The ,-complex is the most stable form of all those considered; the difference between 1 and 2A is 24.9 kcal/mole. A relation between the total energies (kcal/mole) for isomeric forms 2 is established to be 2A (0) < 2B (0.98) < 2C (1.58). Complex 1 is shown to be transformed into 2A via the intermediate formation of 3, which is a hybrid form of the complex (,-complex of mercury chloride with two acetylene molecules). The structures of the transition states for the transformations of 1 into 3 (structure 4) and of 3 into 2A (structure 5) and the corresponding transition activation energies are determined. The interaction of 2A, 2B, and 2C with the Cl- anion as a model nucleophile is considered. It is shown that the resulting anions (6A, 6B, 6C) have a planar structure with the relative stability increasing in the series 6A<6B<6C. 相似文献
20.
Triterpene glycosides from Pulsatilla chinensis 总被引:1,自引:0,他引:1
Glebko L. I. Krasovskaj N. P. Strigina L. I. Ulanova K. P. Denisenko V. A. Dmitrenok P. S. 《Russian Chemical Bulletin》2002,51(10):1945-1950
Four triterpene glycosides were isolated from the roots of Pulsatilla chinensis (Bunge) Regel (Ranunculaceae). Two new glycosides, chinensiosides A (1a) and B (2), were identified as 3-O-[-L-rhamnopyranosyl-(12)--L-arabinopyranosyl]-28-O-[-L-rhamnopyranosyl-(14)--D-glucopyranosyl-(16)--D-glucopyranosyl]-3,23-dihydroxylup-20(29)-en-28-oic acid and 3-O-{-L-rhamnopyranosyl-(12)-[-D-glucopyranosyl-(14)]--L-arabinopyranosyl}-28-O-[-L-rhamnopyranosyl-(14)--D-glucopyranosyl-(16)--D-glucopyranosyl]-3,23-dihydroxylup-20(29)-en-28-oic acid. The other two glycosides were identified as previously known hederasaponin C (3) from Hedera helix and glycoside III (4) from Pulsatilla cernua. 相似文献