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A theoretical study on the water-mediated asynchronous addition between urea and formaldehyde

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Chinese Chemical Letters 2013年第1期24卷 85-88页

作者： Tao-Hong Li xiao-guang xie Guan-Ben Du College of Wood Science and Technology Nanjing Forestry University Faculty of Chemistry Southwest Forestry University Department of Chemistry Yunnan Univerisity

The reaction between urea and formaldehyde in water solution was theoretically investigated by using B3LYP and MP2 methods. It was found that the addition of the nitrogen atom in urea to the carbonyl group in formaldehyde precedes the proton transfer and the proton migration from water to the carbonyl group occurs before the proton abstraction from the nitrogen. With one or two water molecules involved in the TS, the activation energy barrier is lowered compared to the TS of the mechanism with no water participation. The energy change along the reaction coordinate clearly shows that a zwitterionic-like intermediate does not exist on the PES. The reaction between urea and formaldehyde occurs in a concerted mechanism but with asynchronous characters, This is different from the stepwise mechanism recently found for the amination reactions of formaldehyde.

关键词： Urea Formaldehyde Water-mediated Asynchronous Addition

Elimination of HBr from CH_3Br by Cu^+ and Au^+:A DFT study

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Chinese Chemical Letters 2008年第7期19卷 881-884页

作者： Tao Hong Li Chuan Ming Wang Xiang Yi Liu xiao guang xie Faculty of Chemistry Southwest Forestry University Kunming 650224 China Department of Biology Honghe University Menzi 661100 China Department of Chemistry Yunnan University Kunming 650091 China

The elimination of HBr from CH3Br by ground state of Cu＋ and Au＋ has been investigated by using DFT methods. A mechanism of one-step HBr elimination leading to CuCH2＋ was identified. For the formation of AuCH2＋, besides the one-step mechanism, another two-step HBr elimination pathway through a C-Br bond insertion intermediate was also found, and this pathway is energetically more favorable than the one-step mechanism. The calculated reaction energy barriers show that the formation of AuCH2＋ is energetically much more favorable than the formation of CuCH2＋. The experimental observations are well explained.

关键词： Copper and gold Alkyl halide HBr elimination

Theoretical study on the reaction of NbS^+(~3∑^-,~1Γ) with CO

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Chinese Chemical Letters 2009年第6期20卷 755-758页

作者： Shi Wen Yu TaoHong Li xiao Mei Yang Li Qing Yin Li Feng Yao xiao guang xie Department of Chemistry Yunnan University Kunming 650091 China Department of Chemistry Qujing Normal University Qujing 650011 China Faculty of Chemistry Southwest Forestry University Kunming 650224 China Yunnan University of Traditional Chinese Medicine Kunming 650091 China

Two possible reactions of NbS＋（3∑^-, 1Г） with CO in the gas phase have been studied by using B3LYP and CCSD（T） methods： the O/S exchange reaction （NbS^＋＋ CO → NbO^＋＋ CS） and the S-transfer reaction （NbS＋＋ CO → Nb^＋＋ COS）. The two reactions have a one-step mechanism. The barriers of the O/S exchange reaction on the triplet and singlet surfaces are 51.2 and 52.4 kcal/mol, respectively, and the barriers of the S-transfer reaction are 58.3 and 78.0 kcal/mol, respectively. The results indicate that the Stransfer and the O/S exchange reaction of the 3∑^- ground state of NbS＋ are competing, but, for the S-transfer reaction, the 1F exited state is more reactive. The differences between the reactions of NbS＋（3∑^_, 1Г） and VS＋（3∑^_, 1Г） are discussed.

关键词： Niobium sulfide cation CO Reaction CCSD(T)

The Nature of Bonding in WC and WN

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Chinese Chemical Letters 2001年第7期12卷 655-658页

作者： Xue Mei GAO Shi Xi LIU xiao guang xie Huai CAO Shu Shan DAI Department of Chemistry Yunnan University Kunming 650091 Modern Biological Center Yunnan University Kunming 650091

The nature of bonding in the title compounds has been studied by using CASSCF and FOCI techniques. The ground states of WC and WN are found to be 3Δ and 4∑- state arising primarily from:...1(22(21(41(13(1 and ...1(22(21(41(23(1 configuration respectively. WC shows a strong character of covalent bond while WN have obvious character of ionic bond and the dissociation energy of WN is larger than that of WC (6.15 and 5.41 eV respective).

关键词： WC and WN nature of bonding molecular constants CASSCF FOCI

The Nature of Bonding in PtC and PtN

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Chinese Chemical Letters 2001年第6期12卷 541-544页

作者： xiao guang xie Xue Mei GAO Shi Xi LUI Huai CAO Shu Shan DAI Department of Chemistry Yunnan University Kunming 650091 Modern Biological Center Yunnan University Kunming 650091

The nature of bonding in the title compounds has been studied by using CASSCF and FOCI techniques. The ground states of PtC and PtN are found to be (1)Sigma (+) and (2)Pi state arising primarily from:... 1 sigma (2)2 sigma (2)1 pi (4)1 delta (4)3 sigma (2) and...1 sigma (2)2 sigma (2)1 pi (4)1 delta (4)3 sigma (2)2 pi (1) configuration respectively and both of which form triple bond tone sigma, two pi bonds), but the bond of PtC is much stronger than that of PtN.

关键词： PtC and PtN nature of bonding molecular constants CASSCF FOCI

Theoretical study on the reaction of VS^+(~3∑^-,~1Γ)with CO

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Chinese Chemical Letters 2008年第8期19卷 1008-1011页

作者： Shi Wen Yu Li Qing Yin Li Feng Yao Ming Li xiao guang xie Department of Chemistry Yunnan University Kunming 650091 China

Two possible reaction mechanisms of VS^＋（^3∑^-, 1^Г） with CO in the gas phase have been studied by using B3LYP/TZVP and CCSD（T）/6-311＋G （3df, 3pd） methods： the O/S exchange reaction （VS^＋＋CO→VO^＋＋CS） and the S-transfer reaction （VS^＋＋ CO → V^＋＋ COS）. The two reactions proceed via two-step and one-step mechanism, respectively. The barriers of the triplet and singlet PESs are 30.6 and 50.9 kcal/mol, respectively, for O/S exchange reaction and 7.3 and 50.2 kcal/mol, respectively, for the S-transfer reaction. The results indicate that the triplet ground state reaction is more favorable, and the S-transfer reaction is more favorable than the O/S exchange reaction, which is in good agreement with the experimental observation.

关键词： Vanadium sulfide ion CO Reaction CCSD(T)

A computational study on the gas phase reaction of Os^+ with N_2O

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Chinese Chemical Letters 2009年第8期20卷 1010-1014页

作者： Tao Hong Li Chuan Ming Wang Shi Wen Yu Xiang Yi Liu Hui Fu xiao guang xie Faculty of Chemistry Southwest Forestry University Kunming 650224 China Department of Biology Honghe University Menzi 661100 PR China Department of Chemistryl Qujing Normal University Qujing 650011 China Department of Chemistry Yunnan University Kunming 650091 China

The reaction of Os^＋（^6D, ^4F） with N20 has been investigated at B3LYP/TZVP and CCSD（T）/6-311＋G^＊ levels of theory. The mechanisms corresponding to O-atom and N-atom transfer reactions have been revealed. It was found that on the sextet reaction surface both the O-atom and N-atom transfer reactions undergo through direct-abstraction mechanism, leading to the formation of OsO^＋ and OsN^＋, whereas on quartet surface the two reactions undergo through O-N bond or N-N bond insertion mechanism. The calculated energetics shows that the reactions on the sextet surface have notable energy barriers, whereas the reactions on quartet surface are barrierless. ？2009 xiao guang xie. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

关键词： O-Atom transfer N-Atom transfer Abstraction Insertion

Neopeapyran, an unusual furo[2,3b]pyran analogue and turnagainolide C from a soil Streptomyces sp. S2236

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Chinese Chemical Letters 2016年第7期27卷 1044-1047页

作者： Hao Zhou Ya-Bin Yang Rong-Ting Duan Xue-Qiong Yang Ju-Cheng Zhang xiao-guang xie Li-Xing Zhao Zhong-Tao Ding Key Laboratory of Medicinal Chemistry for Natural Resource Ministry of Education School of Chemical Science and Technology Yunnan University Yunnan Institute of Microbiology Yunnan University

Neopeapyran（1）,an unusual furo[2,3b]pyran analogue,together with a new cyclopeptide,turnagainolide C（2）,were isolated from Streptomyces sp.S2236 associated with the rhizosphere soil of Panax *** planar structure and relative configuration of neopeapyran（1） were elucidated on the basis of spectroscopic techniques,while the absolute configuration was determined by TDDFT *** absolute configuration of turnagainolide C（2） was determined by partial hydrolysis,together with the advanced Marfey’s method and spectroscopic *** antimicrobial activities of these two compounds were also investigated.

关键词： Streptomyces sp. Furo[2,3b]pyran analogue Cyclopeptide Structure elucidation Antimicrobial activity

Influence of Vanes and Blades on Ingress in Axial Rim Seal for Turbine Stages

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Journal of Thermal Science 2024年第3期33卷 833-846页

作者： REN Ran DU Qiang LIU guang ZENG Yanlian xie Lei Institute of Engineering Thermophysics Chinese Academy of SciencesBeijing100190China National Key Laboratory of Science and Technology on Advanced Light-duty Gas-turbine Beijing100190China School of Aeronautics and Astronautics University of Chinese Academy of SciencesBeijing100190China

Hot gas ingestion refers to the phenomenon of mainstream hot gas flowing into the space cavity of a turbine *** studies have found that mainstream annulus pressure distribution plays an important role in hot gas ingestion,but due to its complexity,the mechanism of the interaction between mainstream flow and hot gas ingestion remains *** paper adopts the URANS method,and three sealing flow rates are considered,named C_(w)=0,C_(w)=500,and C_(w)=*** time-averaged annulus pressure distribution shows that an increase in the sealing flow decreases the pressure value,and the effects of the sealing flow on the pressure distribution of the leading edge of the blade are much more influential than that of the trailing edge of the *** unsteady pressure time-space distribution in the annulus indicates that a time-space tilted distribution of pressure at the rim exits when the sealing flow *** phenomenon is mainly due to the strong feedback mechanism of the sealing flow to the annulus pressure field.A comparison of the pressure and mean radial velocity distribution of the mainstream shows that the ingestion mainly occurs on the blade side,where the pressure is lower than on the vane *** flow characteristics at the wheel rim are analyzed with a sealing flow rate C_(w)=5000,and under these conditions,both pressure-induced ingestion and ingestion caused by a passage vortex can be *** three-dimensional and inertial effects of the mainstream at the wheel rim lead to the generation of separation vortices on the blade side,and the presence of separation vortices leads to ingestion along the blade *** the same time,pressure on the blade side will cause the fluid to have a radial inward flow tendency,which will promote the formation of separation vortices,leading to more serious ingestion in the high-pressure region on the blade *** blade pressure field can be more significant than the vane trailing pressure field in the rim sea

关键词： separation vortex unsteady rim seal the effect of blade on ingestion