摘要:

AbstractIn addition to having a noninteger value of λ for non‐equivalent hybrid atomic orbitals spλthe introduction of a noninteger occupation number to a valence configuration for atoms in a molecule renders a precise account of the covalent bond in homonuclear diatomic molecules. For instance, the following bond orders 0.05, 1.42 and 2.62 are obtained for the molecules Be2, B2and C2according to the proposed met

ISSN:0009-4536    

DOI:10.1002/jccs.199500100

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThree ab initio calculations (HF/6‐3IG, HF/6‐3IG*, and HF/6‐3IG**) on 2,4,6‐trinitrotoluene were made, The results compare well with xray data, except dihedral angles of NO2relative to the plane of the benzene ring. The deviations are attributed to packing forces and steric effects in the crystal. The most stable structure was a torsional angle 10° of the methyl top with the benzene ring, unlike toluene. The rotational barriers of the methyl top and the 4‐nitro group are small. Hydrogen bonding, dipole moments and total atomic charges arc

ISSN:0009-4536    

DOI:10.1002/jccs.199500101

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractIntroduction of a sample at a programmed temperature is an attractive approach both for dilute samples in large volumes and to prevent discrimination inside the syringe needle with this injection into a capillary gas Chromatograph. Quantitative data obtained with glass liners packed with trapping materials including glass wool, Tenax TA, Chromosorb 101 and Thermotrap‐TA to analyze chlorinated and sulfur compounds are compared. To eliminate the solvent, these vapors were vented through the injection port cap, which provided greater efficiency than through the split lin

ISSN:0009-4536    

DOI:10.1002/jccs.199500102

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe dissociation constant values of glycylglycine were determined at 25 ± 0.1 °C (I = 0.1 mol L−1KNO3) with Potentiometric pH titration in pure water and various mixture of water and organic solvents. The organic solvents used were methanol, ethanol, N, N‐dimethylformamide, dimethylsulfoxide, acetonitrile and dioxane. Initial estimates of the dissociation constants of glycylglycine were refined with ESAP2M computer program. The results obtained are discussed in terms of average macroscopic properties of the mixed solvents and the possible variation in microheterogeneity of the solvation shells around the s

ISSN:0009-4536    

DOI:10.1002/jccs.199500103

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractTwo chelating reagents, disodium N,N′‐dibenzylethylenebisdithiocarbamate 1 and disodium piperazinebisdithiocarbamate 2, were synthesized and used to preconcentrate trace metals in aqueous samples. For analysis of Cu(II) using a UV‐vis spectrometer, Beer's law was obeyed from 5.0 μg L−1to 6.0 mg L−1for reagent 1, and from 0.2 mg L−1to 6.0mg L−1for reagent. 2. The chelation ratio for reagent 1 to Cu(II) was determined to be 1:1, with a formation constant 1.0 × 109M−l. The dependence of extraction and extraction efficiency of reagent 1 on pH was also studied with an atomic absorption spectrometer for nine heavy‐metal ions‐Cu(II), Fe(III), Pb(II), Co(II), Cr(VI), Ni(II), Zn(II), Mn(II) and Cd(II). Except Cr(VI) and Mn(II), the recovery yields of the other seven metal ions were almost quantitative at pH = 4 − 6. The recovery was 82% for Cr(VI) at pH = 4 − 5, and 52%

ISSN:0009-4536    

DOI:10.1002/jccs.199500104

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractWith a phase‐transfer catalyst, Pt‐dppm (dppm = Ph2PCH2PPh2) complexes undergo basic hydrolysis, in which a dppm ligand is hydrolyzed to produce PPh2Me and PPh2OH (or PPh2O). The ease of this hydrolysis reaction depends partly on the molecular charges of the metal complexes. Hydrolysis of neutral [Pt(dppm)(L‐L)] (L‐L = S2CO2, S2P(O)(OEt)2−and mnt = S2C2(CN)22−) is slower than that of monocationic [Pt(dppm)(L′‐L′)]Cl (L′‐V = S2CNEt2‐, (CH2)2S(O)Me and acetylacetonate) compounds. Among the neutral compounds, hydrolysis of [Pt(dppm)(mnt)] is more rapid than that of the other two. These results are rationalized according to the ease with which partial positive charges are induced on the dppm phosphorus atoms. The steric effect due to ligands trans to dppm also influences the rate of hydrolysis of Pt‐dppm compounds. When trans ligands are Ph2P(CH)2PPh2, Ph2P(CH2)3PPh2and (Ph2PO2)H, no hydrolysis of dppm occurs. Hydrolysis of Pt‐dppm compounds depends further on the concentrations of both the phase‐transfer catalyst and OH−ions. All these results are consistent with nucleophilic attack of OH−on dppm phosphorus atoms to r

ISSN:0009-4536    

DOI:10.1002/jccs.199500105

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractCompounds of the type M3[Fe(CN)6]2XH2O (M = Co(II), Ni(II), Cu(II), and Zn(II)) were prepared and magnetic properties of their powders were investigated by means of EPR spectra, Mössbauer effect and magnetic susceptibility measurements. The temperature dependence of the magnetization for the complexes Co3[Fe(CN)5]2‐ 10H2O, Ni3[Fe(CN)6]2‐10H2O and Cu3[Fe(CN)6]2‐4H2O revealed that below the critical temperatures 15, 22 and 20 K respectively, these complexes have zero‐field magnetization. The magnetic hysteresis at 10 K for Co(II), Ni(II) and Cu(II) complexes was observed. Mössbauer spectra at 4.2 K for the compounds are

ISSN:0009-4536    

DOI:10.1002/jccs.199500106

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractWe describe identification of seven components from Antrodia cinnamomea. Their structures were determined on the basis of spectral analysis and comparison with authentic samples. These compounds include two steroids (1, 2) (β‐sitosterol and eburicol), two new steroids (3, 4) [methyl‐4α‐methylergost‐8,24(28)‐dien‐3,7,11‐trion‐26‐oate and methyl‐4α‐methylergost‐8,24(28)‐dien‐3,11‐dion‐26‐oate], two lignans (5, 6) [(+)‐sesamin and 4‐hydroxysesamin], and one long chain methyl ester (7) (methyl oleate). Among them, compound

ISSN:0009-4536    

DOI:10.1002/jccs.199500107

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractEnzymatic hydrolyses of ibuprofen esters produced 99% optically pure S‐(+)‐ibuprofen. The ee values of two enantiomers of ibuprofen were determined on a HPLC equipped with a chiral col

ISSN:0009-4536    

DOI:10.1002/jccs.199500108

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractBromination of 3‐phenylthio‐2‐sulfolene (2) withN‐bromosuccinimide gave 2‐bromo‐3‐phenylthio‐2‐sulfolene (3) which was converted mainly to 2,3‐bis(phenylthio)‐2‐sulfolene (4) by treatment with sodium phenylthiolate. Thermal desulfonylation of 4 at different temperatures in the presence of a base (DBU) yielded stereoselectively the (Z)‐ and (E)‐1,2‐bis(phenylthio)‐1,3‐butadiene (6). These two geometric isomers could be thermally interconverted. The Diels‐Alder reactions of 6 were also investigated. Only the (Z)‐diene 6a could undergo the Diels‐Alder reaction; the (E)‐diene 6b was in situ converted to the Z isomer before undergoing (he Diels‐Alder reaction. The reaction of 6a withN‐phenylmaleimide gave the cycloaddition product 7 with completeendoselectivity, but under daylight or during chromatography it readily underwent a thioallylic rearrangement to yield 8 with inversion of configuration. The cycloaddition of 6a with methyl acrylate proceeded regiospecifically, but generating a mixture ofendoandexoisomers. Theendo/exoratio cou

ISSN:0009-4536    

DOI:10.1002/jccs.199500109

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY