摘要:

AbstractBothcis‐andtrans‐isomers of 4‐(2‐(9‐anthryl) vinyl) pyridine were isolated and their molecular structures established by X‐ray crystallographic method. Variable temperature1H NMR spectroscopy was used to study thetranstocisisomerization of the title compound. The kinetic study of the reaction was based on the ratio of the NMR integration heights in toluene‐d8of the double doublet due to thecis‐isomer at δ 8.51 to that of the multiplet at δ 8. 15 which was kept constant during the whole experiment. The isomerization process was found to be first order and the Arrhenius activation parametersE8, lnA, ΔH≠and ΔS≠were calculated as 27.84 kJ/mol, 6.71, 25.23 kJ/mol and −197.89 J/(K·mol), respectively. Besides, conformational analyses of both compounds based on molecular modeling were carried out and the results were used to compare

ISSN:1001-604X    

DOI:10.1002/cjoc.19990170202

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

年代:1999

数据来源: WILEY

摘要:

AbstractThe influence of bond valence on bond covalence in Lal‐xCaxCrO3(x= 0.0, 0.1, 0.2, 0.3) has been studied by using semi empirical method. This method is the extortion of the dialectic description theory proposed by Phillips, Van Vetches, Levine and Tanaka (PVLT). In the calculation of bond valence, two schemes were adopted. The first is the equal‐valence scheme, and the second is Bond Valence Sums (BVS) scheme. Bath schemes suggest that for the title compound bond covalence be mainly influenced by bond valence, and insensitive to the Ca doping level. Generally speaking, larger bond valences usually result in higher bond covalenc

ISSN:1001-604X    

DOI:10.1002/cjoc.19990170203

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

年代:1999

数据来源: WILEY

摘要:

AbstractFully optimized geometries and electronic structures of amino derivatives of tetrazole are obtained at MP2/6‐31G* level. The tetrazole rings are planar and aromatic for all the amino derivatives of tetrazole. The amino group is not co‐planar with the ring and its conformation is mainly determined by the lone pair electronic repulsion between the substituents and the ring. N(4) atom is more negatively charged and is the most probable coordination site. The energy gaps between LUMOs and HOMOs of 2H‐aminotetrazoles andC‐aminotetrazole neutrals are smaller than those of the corresponding 1H‐isomers andN‐aminotetrazole neutrals respectively. The IR frequencies, thermodynamic properties and temperature‐dependent functions for heat capacities in the fom (a+bT+cT2) in the 300–1000K ran

ISSN:1001-604X    

DOI:10.1002/cjoc.19990170204

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

年代:1999

数据来源: WILEY

摘要:

AbstractSERS technique wae used to study the chemiesorption kinetics of Methylene Blue (MB) on the HNO3‐etched silver surface. The adsorption kinetic parameters were deduced from different vibrational modes at a low concentration of 3.5 × 10−6mol/L, and it showed that MB adsorbed uniformly (monolayerly) on silver surface. However, the adsorptive behavior turned anomalous at relatively higher concentrations and a possible explanation was suggested. In addition, the influence of Cl−ions on the adsorption states of MB was investigated, and it was shown that MB molecules, adsorbed on the silver surface, tended to transform the “lying‐down” state to the “end ‐ on” 4 state after

ISSN:1001-604X    

DOI:10.1002/cjoc.19990170205

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

年代:1999

数据来源: WILEY

摘要:

AbstractThe TiO2gel doped with UO2+2and Eu3+has been prepared by a sol‐gel method. The quenching of the UO2+2emission by Eu3+and the energy transfer from the excited state of UO2+2to the ground state of Eu3+have been investigated. The energy transfer has been studied by the measurement of luminescence lifetime τ, calculation of energy transfer efficiencyWETand energy transfer rateηET. The experimental results indicated that the quenching is combined static and dynamic mechanism, but the static mechanism is domin

ISSN:1001-604X    

DOI:10.1002/cjoc.19990170206

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

年代:1999

数据来源: WILEY

摘要:

AbstractThe single phase La1‐xNaxCu2O4crystals were synthesized by an electrochemical method from molten KOH/NaOH/KNO3at 280–300°C while La2‐yNayCuO4were prepared by precipitation from the same molten salt. The resulting crystals were characterized by using SEM, XRD, EDX and XPS. XPS analysis revealed that the La3d satellite structures of La1‐xNaxCu2O4were quite different from those of La2‐yNayCuO4. These differences have been attributed tyo the changes in crystal structures, bond lengths and covalent character of the metal‐

ISSN:1001-604X    

DOI:10.1002/cjoc.19990170207

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

年代:1999

数据来源: WILEY

摘要:

AbstractThe first chromia‐pillared layered tetratitanate was prepared by the reaction of layered tetramethylammonium tetratitanate with chromium (III) acetate [Cr(OAc)3] aqueous solution and subsequent calcination of the resultant solid product in air at 400°C. The obtained chromia‐pillared layered tetratitanate has an interlayer distance of 1.06 nm and a high thermal stability up to 600°C. It was also found that calcination in N2led to the chromia‐pillared layered tetratitanate with relatively higher Brunauer‐Emmett‐Teller (BET) specific surface area (93.9 m2·g−1) and smaller average pore diameter (4.44 nm) than that in air (82.0 m2·g−1, 7.61 nm). Both Brönsted and Lewis acid sites (mainly Lewis type) are present on the chromia‐Pillared layered tetratitanate (500°C, N2, 8 h) and strong enough to still remain a small proportion of pyridine upon outgassing at 250°C. Moreover, ammonia temperature‐programmed desorption (NH3‐TPD) result showed that there were three NH3desorption peaks at 160, 200 and 315°C, respectively. The corresponding acid amount is 41.3, 73.9 and 290.7μmol·g−1. The tot

ISSN:1001-604X    

DOI:10.1002/cjoc.19990170208

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

年代:1999

数据来源: WILEY

摘要:

AbstractA spectrophotometric method for the determination of chlorhexidine acetate is described. The reaction between chlorhexidine acetate and chloranil took place in an alcohol‐acetone solution at room temperature. The composition of the charge transfer complex is 1:2. Beer's law is obeyed in the concentration range of 15–270 μg·mL−1with correlation coefficient 0.9995. The apparent molar absorptivity is 2.21 × 103L·mol−1·cm−1at 412 nm. The method is accurate (with a recovery af 100 ± 1.6% ) and precise (RSD =1.0%). It was successfully applied to determine chlorhexidine acetate in suppository or disinf

ISSN:1001-604X    

DOI:10.1002/cjoc.19990170209

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

年代:1999

数据来源: WILEY

摘要:

AbstractSystematic studies are made on application of chemometrics to chemical modeling and/or molecular modeling as well as the regularity of retention index for gas chromatography (GC). A set of novel molecular graph theoretical parameters, called the molecular distance‐edge (MDE) vector (λ), is proposed ad found to be excellently correlated to retention index of GC for alkanes. The MDE parameters were tested by the multiple linear regression (MLR) estimation and production of the retention index of GC, and the results obtained are satisfacto

ISSN:1001-604X    

DOI:10.1002/cjoc.19990170210

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

年代:1999

数据来源: WILEY

摘要:

AbstractSpline wavelet and orthogonal wavelet are two widely used wavelet methods. In this paper, comparison of these two methods has been made, including their algorithm, properties and results of signal processing in analytical chemistry signals. It is found that spline wavelet is more effective than orthogonal wavelet in processing high noise signals. The curves obtained from spline wavelet are closer to the theoretical ones than those obtained from orthogonal wavelet and the errors of spline wavelet are smaller than those of orthogonal wavelet.

ISSN:1001-604X    

DOI:10.1002/cjoc.19990170211

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

年代:1999

数据来源: WILEY