MOLECULAR BEAM STUDIES ON ADSORPTION-DESORPTION KINETICS OF CO AND H_2 ON Ni SURFACE

Adsorption-desorption kinetics of CO and H_2 on Ni surface were studied with molecular beam relaxation spectrometry. It is found that there are two adsorbed states in the substrate temperature range 330K相似文献   

STUDIES ON THE REACTION OF ORGANOTELLURONIUM SALTS

The structural studies of the telluronium saltrformation betweendibutyl telluride and secondary (?)-bromo compounds and the use of the obtai-ned salts for the olefination of carbonyl compounds were reported.     

AB INITIO STUDIES ON THE REACTION MECHANISH OF CYCLOADDITION OF KETENE AND FORMALDEHYDE

The cycloaddition reaction of ketene and formaldehyde,lesding to 2-oxetanone,has been studied theoretically by means of RHF/3-21G.This reactionis believed to be nonsynchronous but concerted,taking place through a twistedfour membered ring transition state.Two types of frontier orbitalinteractions are involved in this reaction.The activation barrier iscalculated to be 123.1KJ/mol (MP2/3-21G result).     

STUDIES OF TPSR AND PULSE REACTION OF METHYL IODIDE ON SILICA-SUPPORTED NOBLE METAL CATALYSTS

IntroductionAttcn1ptstoclucidatcthcmcchanismofCtOh}drogcnationontransitionmctalcatal\stsbyusingprobcmoIcculcscanbctraccdbacktoatlcastascarl}'asl95ll]lAlthoughthistcchniqucisanindircctx"a}'ofstud}'ingsurfaccrcactionmcchanisms.itallot"sustostud}'inslIusurfaccrcactionsundcrccrtainconditionsx"hichusualI}'cannotbcprobcdb}'morcdirectinstrumcntalmcthodssuchassurfaccspcctrosc0pictcchniqucsOfintcrcstisthcreccntt"orkrcp0rtcdb}'Bclgucdl2l'KocrtsI3jandYa.l4j\"hoachict'cdthcconvcrsionofmethanctotbrmC2~…     

STUDIES ON THE KINETICS OF PHASE TRANSITIONS OF A MAIN CHAIN THERMOTROPIC POLYESTER

The kinetics of phase transitions including a transition between mesophases were studied for a main-chain thermotropic polyester by means of DSC and depolarizing transmittance techniques. The isothermal process of these transitions was found to be described by the Avrami equation to high conversions. The Avrami exponents n are about 2,4, 5.3 and 2.2 for liquid crystallization, transition between mesophases and crystallization from mesophase respectively. The liquid crystallization from isotropic liquid phase occurs at very low undercoolings with high transformation rate. This behavior is explained as the results of the smaller value of the surface free energy for mesophase than that for crystallites which is evidenced by the very weak temperature dependence of liquid crystallization rate.     

STUDIES ON THE PHOTOCHEMICAL REACTION OF TERTIARY AROMATIC AMINES AND ALIPHATIC HALIDES——STRUCTURE OF THE PRODUCT AND MECHANISM OF THE REACTION

The photochemical reaction of aromatic amines in the presence of aliphatic halides and molecular oxygen were studied. There is a very obvious structural effect of amines on the photoreactions, and the purple products, formed only in the tertiary aromatic amines system, were proved to be amiuium radical salts, e. g. CH_3—(CH_3)_2Cl-by moans of UV, NMR and ESR spectroscopies electronic conductivity and chemical analysis. The purple product can oxidize the adrenaline to adrenochrome. The mechanism of the photoreaction and the oxidation were discussed.     

MCSCF STUDIES ON THE IRC AND REACTION RATE CONSTANTS FOR THE DEHYDROGENATION REACTION OF VINYL RADICAL

The transition state(TS) and Intrinsic Reaction Coordinate (IRC) for the titled reaction were traced by means of MCSCF/6-31G (210 configurations). The reaction activation energy of this reaction is 140.2KJ/mol. The reaction rate constants of five temperetures were calculated by CVT involving the tunneling effects.     

STUDIES ON THE REACTION MECHANISM OF ORGANIC HYDROPEROXIDE AND AMINE SYSTEM INITIATED POLYMERIZATION

The initiation mechanism of organic hydroperoxide and amine system has been investigatedsystematically in this paper. It has been confirmed from the IR spectra that organic hydro-peroxide could form hydrogen-bonded complex with amine. The reactive intermediate of theamine and its effect on initiating polymerization have been determined by using ESR techni-que, and further proved by the results of polymer end group analysis and graft copolymeri-zation of vinly monomer onto the amino-containig polymer. Finally, water, as one of the finalproducts of ROOH-amine reaction has been detected through chromatographic analysis, fromwhich the conversion reaction of the reactive intermediate is verified.     

STUDIES ON THE KINETICS OF PHOTOPOLYMERIZATION OF ACRYLONITRILE INITIATED BY ANILINE

The dependence of the rate of polymerization on the aniline concentration in the photopolymerization of acrylonitrile initiated by aniline was studied.The rate of polymerization of acrylonitrile increased with increasing of the aniline concentration and showed a maximum at first, then showed another increase after a minimum.This phenomenon was explained with the extinction coefficient of aniline at 313 nm,334 nm and 365 nm wavelengths.Similar results were obtained for the aniline derivatives.Therefore, the initiator exponents in the photopolymerization varies with the different concentrations of initiator and the square-root dependence can be obtained only at certain low concentrations, i.e. with low absorbance.     

KINETICS STUDIES OF MINERAL-WATER REACTIONS IN HYDROTHERMAL FLOW SYSTEMS AT ELEVATED TEMPERATURES AND PRESSURES

This paper describes new experimental results on mlneral-water reaction kinetics obtained in plug-flow systems at high temperatures and pressures. As an example, the rates of reaction between calcite, fluorite, albite and water in the continuous flowing system have been measured in three separate studies. All experiments are carried out by suspending a sample bag in the plug-flow vessel, by pumping water at carefully controlled rates through the vessel, and by collecting and analyzing the reacted solution. In addition, the reaction mechanisms of fluorite and albite in a packed bed reactor have been studied with the aid of an axial dispersion model. The main factors controlling the effective dissolution rate with respect to temperature, solvent flow rate, and chemistry of the input solutions have been evaluated. It is also found that a non-steady state process is, in some cases, still observed, even under conditions where steady state conditions should have been attained. These results provide informatio     

INFLUENCE OF SAMPLE THICKNESS ON ISOTHERMAL CRYSTALLIZATION KINETICS OF POLYMERS IN A CONFINED VOLUME

Isothermal crystallization process of polymers in a confined volume was simulated in the case of instantaneous nucleation by use of the Monte Carlo method. The influence of sample thickness on some kinetic parameters of crystallization was quantitatively evaluated. It was found that there was a critical thickness value. Influence of thickness on the crystallization behavior was only found for samples of thickness near and less than the critical value. For thick samples the Avrami plot showed straight lines with a turning point at the late stage of crystallization due to the secondary crystallization. When the thickness was near or less than the critical value a primary turning point appeared in the Avrami plot at the very beginning of the crystallization process. A model was proposed to explain the mechanism of this phenomenon. According to this model the critical thickness value is related to the nucleation density or the average distance between adjacent nuclei, and the primary turning point is an indication of a transformation of crystal growth geometry from a three-dimensional mode to a two-dimensional one. Analysis of experimental results of PEO isothermally crystallized at 53.5℃ was consistent with the proposed model.     

STUDIES ON THE WITTIG REACTION(XIII): KINETICS OF THE PTC-WITTIG REACTIONS OF 2-BUTENYL METHYL-DIPHENYLPHOSPHONIUM SALT WITH SUBSTITUTED BEN2ALDEHYDES

The kinetics of PTC-Wittig reaction between substitutedaromatic aldehydes and 2-butenyl methyldiphenylphosphonium salthas been studied. The low reaction constant (ρ=0. 30) impliesthat these PTC-Wittig reactions take place through low polarintermediate.     

MCSCF AND VTST STUDIES OF THE REACTION CH(2~π)+H_2→CH_3

ＭＣＳＣＦＡＮＤＶＴＳＴＳＴＵＤＩＥＳＯＦＴＨＥＲＥＡＣＴＩＯＮＣＨ（２~π）＋Ｈ_２→ＣＨ_３￥ＳｉＹｕＭＡａｎｄＲｕｏＺｈｕａｎｇＬｉｎ（ＤｅｐａｒｔｍｅｎｔｏｆＣｈｅｍｉｓｅｄ．ＢｅｉｊｉｎｇｆｏｒｍａｌＵｎｉｖｅｒｓｉｔｙ，Ｂｅｉｊｉｎｇ１００?..     

STUDIES ON DOPAMINE RECEPTORS AND TETRAHYDROPROTOBERBERINES．Ⅱ．QUANTUM CHEMISTRY OF LIGAND－RECEPTOR INTERACTION

ＳＴＵＤＩＥＳＯＮＤＯＰＡＭＩＮＥＲＥＣＥＰＴＯＲＳＡＮＤＴＥＴＲＡＨＹＤＲＯＰＲＯＴＯＢＥＲＢＥＲＩＮＥＳ．Ⅱ．ＱＵＡＮＴＵＭＣＨＥＭＩＳＴＲＹＯＦＬＩＧＡＮＤ－ＲＥＣＥＰＴＯＲＩＮＴＥＲＡＣＴＩＯＮ￥ＹｕｎＴＡＮＧ；ＫａｉＸｉａｎＣＨＥＮ；Ｈｕａ...     

A SUMMARY OF STUDIES ON Mo-Fe-S CLUSTER COMPOUNDS WITH MoFe_3S_4 UNIT

<正> INTRODUCTION. Biochemical and spectroscopic studies on MoFepr of nitrogenase or its molybdenum site—FeMoco have shown that Mo-Fe-S cluster cc(?)stitutes the basic skeleton of this site. Many attempts have been made in synthesizing Mo-Fe-S cluster compounds as chemical models. It is the expectation of chemists to find the key to nitrogen fixation through studies of model compounds.     

STUDIES ON RNA LIGASE ACTIVITY IN THE BRAIN AND LIVER CELLS OF MOUSE

RNA ligase in eukaryotic mammalian cells was studied by using mouse brain and livercell extracts as enzyme sources and Oligo A as substrates. RNA ligase activity was deter-mined by measuring the formation of alkaline phosphate-resistant product from 5'-~32P-termi-hated Oligoribonucleotides. Under appropriate conditions, the activity of this enzyme inbrain and liver cells may vary between 16-49 mU/ml. The joining way between donorand acceptor is 5'-P→3'-OH. Further studies wore carried out by using synthetic UpCpUand ~32pNp as substrates and crude enzyme preparations from extracts of cell unclei of brainand liver as enzyme sources. RNA ligase activity was examined by homochromatographyand autoradiography. A clear joining product was demonstrated and then isolated from thereaction mixture by DEAE-Sephadex A25 column chromatography. The eluted fractionswere identified by DEAE-cellulose thin layer chromatography. The joining product washydrolyzed either with KOH or with alkaline phosphatase, the autoradiog     

EFFECTS OF BAICALEIN, WOGONIN, BAICALIN AND Na2MoO_4 ON N-NITROSATION REACTION

The in vitro effects of baicalein,wogonin,baicalin and Na_2MoO_4 on N-nitrosation reaction have been studied. The N-nitrosation reaction has been determined by the amount of dimethylnitrosamine(DMN) and diethylnitrosamine(DEN) produced using the UV-photclysis spectrophotometric and pyrolysis gas chromatography test. Baicalein,wogonin and Na_2MoO_4 showed varing extents of inhibition of the formation of DMN and DEN. Baicalin promoted the formation of DMN and DEN under the condition of simulating gastric Juices. It is also found that E. coli showed a remarkable promoting effect on the formation of DMN and DEN,but this promoting effect could be blocked to some extent by baicalein,wogonin,baicalin and Na_2MoO_4. Besides, Na_2MoO_4 and wogonin have shown synergic effect on the blocking of N-nitrosation reaction.     

THEORETICAL STUDIES ON THE CYCLOADDITION REACTION OF FLUOROKETENE WITH ETHYLIDENIMINE

ＴＨＥＯＲＥＴＩＣＡＬＳＴＵＤＩＥＳＯＮＴＨＥＣＹＣＬＯＡＤＤＩＴＩＯＮＲＥＡＣＴＩＯＮＯＦＦＬＵＯＲＯＫＥＴＥＮＥＷＩＴＨＥＴＨＹＬＩＤＥＮＩＭＩＮＥＴＨＥＯＲＥＴＩＣＡＬＳＴＵＤＩＥＳＯＮＴＨＥＣＹＣＬＯＡＤＤＩＴＩＯＮＲＥＡＣＴＩＯＮＯＦＦＬＵ...     

STUDIES ON SYNTHESES OF MoFe_3S_4 CUBANE-LIKE CLUSTER COMPOUNDS

The features of synthetic processes are described on the basis of the studies of the syntheses of MoFe_3S_4 cubane-like cluster compounds either by self-assembly reactions or by the conversion of linear clusters. The redox properties and the structure of ligands as well as the stoichiometry of reactants have obvious effects upon the core oxidation state and the structure of products. It is indicated that the self-assembly reaction may pass through a combination process oflinear cluster intermediates having structural unit (M,M'=Mo) Fe).