摘要:

Abstract4,4‐Dimethoxy‐2,5‐cyclohexadienones9–14were prepared from the corresponding hydroquinone monomethyl ethers by oxidation with thallium trinitrate in methanol. Irradiation of solutions of9–13in methanol with a broad band of UV light centered at 350 nm in a Rayonet reactor afforded 2‐cyclopentenone derivatives15–19in moderate to excellent yields, whereas irradiation of14in methanol gave phenol 8 along with other unidentified products. Irradiation of11–14in benzene yielded substituted phenols. The plausible reaction pathways for the product formatio

ISSN:0009-4536    

DOI:10.1002/jccs.199800001

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractFrom recent accurate ab initio calculation on [N]phenylenes by Schulman and Disch, some regular patterns for bond alternation and energy increment can be found. We interpreted these results by considering a “unit cell” of interior benzene rings fused to two four‐membered rings in either linear or angular fashion. Our model works better in accounting for the structure than for the e

ISSN:0009-4536    

DOI:10.1002/jccs.199800002

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe stopped‐flow fluorescence traces for the hydrolysis of Leu‐Ala‐DED catalyzed byStreptomyces griseusaminopeptidase isolated from pronase exhibits a two‐phase fluorescence change with comparable rates of formation and breakdown of the ES complex. We have developed a method for the determination of the individual rate constants from the stopped‐flow traces. The kinetic parameters for the enzyme‐catalyzed hydrolysis of Leu‐Ala‐DED at 25 °C and pH 8.0 are:k1= (1.6±0.1) × 105M−1s−1,k−1, = 0.089 ± 0.001 s−1, andk2= 0.58 ± 0.01 s−1. For the observed stopped‐flow traces, the steady state approximation is valid only within a very small region around the maximal ES concentration and a large proportion (>20%) of the substrate has already been hydrolyzed during the pre‐steady state. For a very fast formation of ES complex, the steady state approximation is valid for almost the entire trace. The activation energies for each individual rate constant were determined to be 10.0 ± 0.7, 35 ± 5, and 21.2 ± 0.8 kcal mol−1fork1, k−1, and k2, respectively. Binding of E and S to form ES was accompanied by a decrease in Gibbs free energy, whereas a dramatic increase in free energy was observed for the conversion of ES to ES≠. The dissociation of ES to form E and S had a very large activation energy, but it was also

ISSN:0009-4536    

DOI:10.1002/jccs.199800003

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractTwenty‐three rovibronic levels of the Na243σ+gstate were observed by pulse perturbation‐facilitated optical‐optical double resonance (PFOODR) excitation spectroscopy through the A1σ+u‐b3πu, mixed intermediate levels. The molecular constants and the Rydberg‐Klein‐Rees (RKR) potential energy curve of the 43σ+gstate are deriv

ISSN:0009-4536    

DOI:10.1002/jccs.199800004

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractA series of radical complexes containing manganese carbonyl, 1,3,6,8‐tetramethyl‐9,10‐phenanthroquinone (PQ1), 2,4,5,7‐tetramethyl‐9,10‐phenanthroquinone (PQ2) and triphenylphosphine are prepared and their ESR spectra are recorded and analyzed with computer simulations. From the analysis of the proton, manganese and phosphine hyperfine splitting constants, the nature of the orbital interaction and also the election transfer character are revealed. PQ1−and PQ2−Mn(CO)4radicals are of more anion radical character than the unsubstituted PQ−Mn(CO)4radical. The fact that the Mn and P hfsc increases and the proton hfsc decreases as the phosphine ligand increases indicated that an increasing interaction exists between the PQ pπ* and the Mn dπ orbitals with increasi

ISSN:0009-4536    

DOI:10.1002/jccs.199800005

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe vibrational structures of photoelectron spectra can reveal the bonding nature of molecular orbitals. For diatomic molecules the bonding nature of molecular orbitals can be rationalized by the concepts of non‐bonding lone pair type and bonding type bond orbitals consisting of Lewis structures.For the simplest polyatomic molecules XY2the concepts of nonbonding lone pair type and bonding type bond orbitals and the method of expanding the canonical molecular orbitals into the bond orbitals are not quite appropriate.Two correlation diagrams, the distance correlation diagram and the angle correlation diagram, provide us with a better theoretical tool. The molecular orbital with the energy curve having positive slope in the distance correlation diagram (or angle correlation diagram) is identified as the R‐bonding (or 9‐bonding) orbital. The removal of an electron from the R‐bonding (or θ‐bonding) gives rise to vibrational excitation with decreasing frequency for the bond stretching (or bending) mode in the photoelectr

ISSN:0009-4536    

DOI:10.1002/jccs.199800006

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe use of chelating agent‐modified Nafion®‐coated mercury‐film electrodes (CNCMFEs) in square wave anodic stripping voltammetry (SWASV) for the determination of trace metals is described. The CNCMFE containing appropriate amounts of dimethylglyoxime (DMG) was applied for the determination of Ni(II), Cd(II), and Cu(II). A similar system that contains 2,2′‐bipyridyl (Bpy) was used for the determination of Pb(II). The effect of various model organic substances on the CNCMFEs in SWASV is thoroughly explored. The CNCMFEs are considerably more resistant to organic interferences than the Nafion®‐coated MFE. The implications of these interferences for the reliability and feasibility of stripping measurements using the CNCMFEs in real samples are discussed. Results presented for real samples demonstrate the analytical utility of the CNC

ISSN:0009-4536    

DOI:10.1002/jccs.199800007

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe feasibility of employing capillary zone electrophoresis to separate nanostructured gold particles was investigated. The optimal experimental conditions of rinsing procedure, type and concentration of cationic surfactant, buffer concentration, and pH value were identified for the separations. Under the optimal conditions — included rinsing capillary with 0.5 N NaOH, water, and buffer for 3 min in sequence, and running the experiment with 7.5 mM TTAB, 12.5 mM tetraborate, and pH 9.0 of buffer solution at 20 kV applied voltage — nearly resolved separation (Rs= 1.0) of gold particles with mean diameter differences as small as 1 nm was achie

ISSN:0009-4536    

DOI:10.1002/jccs.199800008

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractAromatic diamines — such as m‐, p‐phenylenediamine, 2‐nitro‐p‐, N‐phenyl‐p‐phenylenediamine, 2,4‐diaminoanisole, and 2,5‐diaminetoluene — were determined by differential pulse voltammetry (DPV) on a carbon paste electrode with acetate buffer/(pH 4.74). Some factors affecting the determination of dye intermediates were discussed. The method permitted determination of various types of dye intermediates without any pretreatment in commercial hair dyes. The results obtained were in good agreement with those of the high performance liquid chroma

ISSN:0009-4536    

DOI:10.1002/jccs.199800009

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractIn this work, Raman spectra were taken continuously from CuSO4‐5H2O powders during a dehydration process at temperatures up to 400 °C. The spectra showed the variation in structures for both SO42and H2O. Furthermore, the band positions, band intensities, and their derivatives also showed these variations in structure and the amount of each component. From the intensities of the OH bands the amounts of water lost were found to be 2:2:1 in three stages as indicated by TGA/DTA. This method of monitoring variations in structure by Raman spectroscopy as a function of temperature can identify individual species and could be important to the study of a material's thermal properti

ISSN:0009-4536    

DOI:10.1002/jccs.199800010

出版商:WILEY‐VCH Verlag    

年代:1998

数据来源: WILEY