摘要:

AbstractAb initioLCAO‐MO‐SCF calculations for several typical molecules containing phosphorus have been undertaken to study the role of phosphorus 3d orbitals in the bonding. It is emphasized that the discussion about the 3d orbital participation in bonding should be based on a reasonable choice of basis sets and it seems suitable to choose the atomic orbitals in proper molecular environment as the basis set. As an approximation, the optimized minimal STO‐NG basis sets have been adopted in the present paper. The results obtained well exhibit the model of 3d orbital participation in bonding. It is shown that under the influence of highly electronegative ligands the phosphorus 3d orbitals contract greatly, their energy levels drop considerably, and thus they can effectively participate in bonding. The presence of highly electronegative ligands seems necessary. The contribution of 3d orbitals to bonding is achieved mainly through the concerted formation of σ bonds and p‐d backbonds, though the contribution to σ bonding is minor. The three‐center, four‐electron bond model is only approximately correct. The results of the present paper demonstrate that the model of 3d orbital participation in bonding favoured by experimental chemists is reasonable and possesses

ISSN:1001-604X    

DOI:10.1002/cjoc.19920100201

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1992

数据来源: WILEY

摘要:

AbstractAn extremely simple formula to estimate the heat of formation of complexes between an ion and a polar molecule or between highly polar systems is presented. The formula is entirely electrostatic and the expression used is verified by means of perturbation theory. This formula is tested for several ion‐molecule and molecule‐molecule pairs. It is also applied to estimate the heat of hydration of simple sa

ISSN:1001-604X    

DOI:10.1002/cjoc.19920100202

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1992

数据来源: WILEY

摘要:

AbstractThe algorithm of Rayleigh intensity correlation is employed for the elucidation of relaxation time constants of the aqueous NH4H2PO4solution with various concentrations. The result shows that there is a discontinuous (abrupt) increases in the relaxation time constant as the super‐saturation state is reached. This quantity, the relaxation time constant, therefore, can be an order parameter. Also discussed is the dependence of the relaxation time constant on the aggregation numbernin (H2PO4−)n. This dependence is complicated and may be crucial in understanding the aggregation process in the supersaturation st

ISSN:1001-604X    

DOI:10.1002/cjoc.19920100203

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1992

数据来源: WILEY

摘要:

AbstractThe stability constants of complex anion In(tiron)−in mixed solvents of ethanol‐water with weight percentages of ethanol being 0,5,15,25,35 and 50 have been measured spectrophotometrically at 293 K, using NaClO4as supporting electrolyte with ionic strength ranging from 0.1 to 3.3mol·dm−3. The thermodynamic stability constants of In(tiron)−in various mixed solvents have been obtained by a polynomial approximation equation based on Pitzer's theory. As a comparison, the traditional Debye‐Hückel equation has also been used to treat the same data. The results show that this polynomial approximate method is obviously superior to the old one. It was discovered that there is a linear relation between the thermodynamic stability constants of In (tiron)−and the mole fraction of organic component in mixed solvents or the reciprocal of dielectric constants of mixed solvents. The medium effect and the standard free energy of transfer,ΔG°tr, for the coordination reaction: In3++ tiron4‐= In(tiron)−have

ISSN:1001-604X    

DOI:10.1002/cjoc.19920100204

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1992

数据来源: WILEY

摘要:

AbstractThe synthesis and the structural characterization of the title compound H2Na3[W3O(CCH3)‐(O2CCH3)6(H2O)3][H2W12O40]·13.5H2O are described. It is known that the mixed oxo‐ethylidynecapped tritungsten cluster can be obtained by Zn dust reduction of Na2WO4·2H2O in acetic anhydride. The title compound has been characterized by X‐ray diffraction, UV/VIS and1H NMR spectra. The tungsten atoms in the cluster cation and anion are in the oxidation states of W(IV) and W(VI) respectively. The crystal is rhombohedral with the space groupR32,a= 17.058 (3)Å,c= 49.665 (9)Å, γ=120°,V=12516(9)Å3,Z=6, finalR= 0.037 for 2071 reflections withI≥3σ (I). Both the cluster cation and anion have a C3symmetry. The important interatomic distances in angstroms for the cluster cation are: W—W, 2.730(2); W—μ3−O, 2.00; W—O (carbo

ISSN:1001-604X    

DOI:10.1002/cjoc.19920100205

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1992

数据来源: WILEY

摘要:

Abstractn‐In2S3has been prepared by CVT method. The photoelectrochemical behavior of n‐In2S3in a polysulfide redox solution was investigated. It was found that photoetching remarkably increased the fill factor. The maximum quantum efficiency of carrier collection reached 95% after 12h irradiation at 100 mW/cm2at an applied potential of + 1.2 V. XPS and Auger analysis were carried out for examining surface and bulk concentration. The photoetching effect could be satisfactorily explai

ISSN:1001-604X    

DOI:10.1002/cjoc.19920100206

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1992

数据来源: WILEY

摘要:

AbstractA computer‐assisted method is presented for simultaneous optimization of pH and ion concentration selection for the optimal separation in reversed‐phase HPLC. The method is based on a polynomial estimation from nine preliminary experiments according to two‐factor rectangular design. This is followed by a two‐dimension computer scanning technique. Resolution is used as the selection criterion. Good agreement was obtained between predicted data and experimental

ISSN:1001-604X    

DOI:10.1002/cjoc.19920100207

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1992

数据来源: WILEY

摘要:

AbstractThe reaction between chloranil andN−benzyldihydronicotinamide (BNAH) in borate buffer/DMF was investigated. The reaction mixture gave a strong esr signal, which is consistent with that of chloranil anion radical, and tetrachlorohydrophenol (QH2) andN−benzylnicotinamide (BNA+) were obtained as the sole products. When the reaction was run in benzene solution, a green coloured charge‐transfer complex between the reactants could be isolated, which decomposed in polar solvents to give BNA+and QH2. Based on kinetic studies by esr spectroscopy by the stopped‐flow technique, a two‐step electron‐transfer mechanism for the reaction is proposed in contrast to the hydride‐transfer mechanism reported in t

ISSN:1001-604X    

DOI:10.1002/cjoc.19920100208

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo new dolabellane diterpenoids named clavudiolB(2)and clavirolideF(5), have been isolated from the soft coralClavularia viridis, collected from Xisha Islands in the South China Sea. Their structures have been determined as2and5by spectral analysis and chemical reactions.

ISSN:1001-604X    

DOI:10.1002/cjoc.19920100209

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1992

数据来源: WILEY

摘要:

AbstractMNDO and MM2 (85) methods were used to study the conformation and the structure‐reactivity relationship of neutral and acidic phosphorus esters. The calculation results indicate that for the most stable conformation, the charge density of phosphoryl oxygen (qo) is determined not only by the electronegativity of the substituents, but also by the conformation of the alkoxyl groups on the phosphorus atom. Meanwhile, the conformation of the alkoxyl group provides, as a rule, more important influence on the charge density of the phosphoryl oxygen. However, the energy of the highest occupied molecular orbital (EHOMO) is basically dependent on the eletronegativity of the substituents, while the donating ability or the withdrawing ability of the neutral phosphorus compounds is mainly governed by theEHOMObut not the qO. This is also true for other kinds of the neutral oxygen‐containing compou

ISSN:1001-604X    

DOI:10.1002/cjoc.19920100210

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1992

数据来源: WILEY