CF3O2自由基和NO反应机理的理论研究

用密度泛函理论(DFT)的B3LYP方法, 分别在6-31G、6-311G、6-311+G(d)基组水平上研究了CF3O2自由基和NO反应机理. 研究结果表明, CF3O2自由基和NO反应存在三条可行的反应通道, 优化得到了相应的中间体和过渡态. 从活化能看, 通道CH3O2+NO→IM1→TS1→IM2→TS2→CF3O+ONO的活化能最低, 仅为70.86 kJ•mol-1, 是主要反应通道, 主要产物是CF3O和NO2. 而通道CH3O2+NO→IM1→TS3→CF3ONO2和CH3O2+NO→TS4→IM3→TS5→IM4→TS6→CF3O+NOO的活化能较高, 故该反应难以进行.     

烃自由基结构、稳定性和烷烃氯代反应选择性的理论研究

碳自由基是有机化学反应中的一类重要活性中间体,研究不同类型碳自由基的结构及稳定性对阐明有机反应机理及反应选择性具有重要意义。本文运用密度泛函理论,探讨了碳自由基的结构及稳定性,旨在帮助学生理解其结构特征及稳定性规律,并为理解相关反应提供坚实的理论基础。此外,我们还深入探讨了烷烃氯代反应的选择性,加强了学生对烷烃自由基取代反应的认识,使他们更全面地掌握这一主题。     

CH自由基和NO~2反应研究: I. 反应的热力学计算

探讨了CH自由基与NO~2反应的可能路径,通过计算确定了反应物,产物和稳定中间体的电子状态和平衡构型,并运用Gaussian-3方法和MRCISD方法对可能的反应路径进行了热力学计算。在多数情况下与实验值符合较好。对于个别与理论计算差别较大的实验值进行了评述。     

Af型自由基均聚反应的固化理论（1）

利用高分子统计方法，通过引入引发几率及链增长几率，得到了Ａｆ型非线性自由基均聚反应的溶胶及凝胶化条件，进一步利用Ｌａｇｒａｎｇｅ展开定理，得到了体系的数量分布函数，并证明了分布函数的不变性，从而简化了凝胶点后各种平均高分子物理量的表征。     

CH3O与ClO双自由基反应机理的量子化学研究

在QCISD(T)／6—311 G(d,p)／／B3LYP／6．311 G(3df,3pd)水平上,对CH3O与CIO自由基反应进行了理论研究．结果表明,该反应共有三个反应通道,产物分别为HOCI CH2O,CH2O HCl和CH3CI O2(1△)．不论从动力学角度,还是从热力学角度看,形成产物HOCl CH2O的通道均是最有利的,因此为主要反应通道,这与实验观察到的结果是一致的．     

CH自由基和NO~2反应研究: I. 反应的热力学计算

探讨了CH自由基与NO~2反应的可能路径,通过计算确定了反应物,产物和稳定中间体的电子状态和平衡构型,并运用Gaussian-3方法和MRCISD方法对可能的反应路径进行了热力学计算。在多数情况下与实验值符合较好。对于个别与理论计算差别较大的实验值进行了评述。     

C_（60）与n－Bu_3SnH的自由基反应研究

Ｃ_（６０）与ｎ－Ｂｕ_３ＳｎＨ的自由基反应研究余益民，郭兴华，刘子阳，刘淑莹，傅芳信，钱明星（中国科学院长春应用化学研究所，长春，１３００２２）（东北师范大学化学系）关键词自由基反应，富勒烯，三丁基锡氢化物，自由基海绵自Ｋｒａｔｓｃｈｍｅｒ等［１］实...     

传能反应O（^1D）＋CO2（1∑g^＋）→O（^3P）＋CO2（1∑g^＋）中间物机理的理论研究

利用ab initio量子化学方法研究了自旋禁阻的传能反应O(^1D) CO2(1∑g^ )→O(^3P) CO2(1∑g^ )的反应机制，通过中间化合物CO3的单、三重态的势能面交叉点的确认，证明了中间物传能机理的可行性，同时计算了交叉点处的自旋-轨道偶合和面间跃迁几率，进一步证明了中间化合物CO3的形成在传能过程中的重要作用。     

C2H3和NO2反应势能面的理论研究

在CCSD(T)／6—311G(d，p)／／B3LYP／6—3llG(d，p)水平上给出了反应C2H3 NO2的详细势能面信息，并列出了中间体和过渡态的几何构型．通过深入分析反应路径及反应机理，得到5个能量可行的产物和6条反应通道，其中产物C2H3O NO的形成又有利，而产物CH2CO HNO则是次要产物，其他产物在通常条件下可以忽略．     

Theoretical Study of the C_(60)O_3 Isomers

WiththepreparationandisolationofC,,O.'moreandmoreattentionwaspaidtotheirstructuresandpropertiest').WooddetectedC,,O.firstwhentheypreparedC,,byvaporizinggraphite").Fromthenon,thelaboratoriesallovertheworldhavepreparedC6,O.byvariousmethodssuchasPhotoxidationt2-4),Electrochemicaloxi-dation[si,Ozonizationt7.83andChemicaladditiont6'12-14iandsoon.Accordingtothefollow-uptheoreticalstudiesforC,,O.,itisindicatedthattherearetwoisomersofC,,O:eithertheoxygenatomislocatedoverthe6/6bondtogeneratethe6/…     

Kinetics of the R + HBr RH + Br (CH3CHBr, CHBr2 or CDBr2) equilibrium. Thermochemistry of the CH3CHBr and CHBr2 radicals

The kinetics of the reaction of the CH₃CHBr, CHBr₂ or CDBr₂ radicals, R, with HBr have been investigated in a temperature-controlled tubular reactor coupled to a photoionization mass spectrometer. The CH₃CHBr (or CHBr₂ or CDBr₂) radical was produced homogeneously in the reactor by a pulsed 248 nm exciplex laser photolysis of CH₃CHBr₂ (or CHBr₃ or CDBr₃). The decay of R was monitored as a function of HBr concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature. The reactions were studied separately from 253 to 344 K (CH₃CHBr + HBr) and from 288 to 477 K (CHBr₂ + HBr) and in these temperature ranges the rate constants determined were fitted to an Arrhenius expression (error limits stated are 1σ + Student’s t values, units in cm³ molecule⁻¹ s⁻¹, no error limits for the third reaction): k(CH₃CHBr + HBr) = (1.7 ± 1.2) × 10⁻¹³ exp[+ (5.1 ± 1.9) kJ mol⁻¹/RT], k(CHBr₂ + HBr) = (2.5 ± 1.2) × 10⁻¹³ exp[−(4.04 ± 1.14) kJ mol⁻¹/RT] and k(CDBr₂ + HBr) = 1.6 × 10⁻¹³ exp(−2.1 kJ mol⁻¹/RT). The energy barriers of the reverse reactions were taken from the literature. The enthalpy of formation values of the CH₃CHBr and CHBr₂ radicals and an experimental entropy value at 298 K for the CH₃CHBr radical were obtained using a second-law method. The result for the entropy value for the CH₃CHBr radical is 305 ± 9 J K⁻¹ mol⁻¹. The results for the enthalpy of formation values at 298 K are (in kJ mol⁻¹): 133.4 ± 3.4 (CH₃CHBr) and 199.1 ± 2.7 (CHBr₂), and for α-C–H bond dissociation energies of analogous compounds are (in kJ mol⁻¹): 415.0 ± 2.7 (CH₃CH₂Br) and 412.6 ± 2.7 (CH₂Br₂), respectively.     

Comments on “The use of MoO3 and NiO (pure or mixed) oxide catalysts in the decomposition of KMnO4” by S.A. Halawy and M.A. Mohamed

The recent paper by Halawy and Mohamed [S.A. Halawy, M.A. Mohamed, Thermochim. Acta 345 (2000) 157] has raised several problems which need to be resolved. Our comments are given under the headings of the sections of the original paper.     

CH2=CHCl与O(3P)反应的理论研究

用量子化学密度泛函理论和QCISD(Quadratic configuration interaction calculation)方法,对0(^3P)与CH2CHCl的反应进行了理论研究．在UB3LYP／6—311 G(d,p),UB3LYP／6—31 (3df,3pd)计算水平上,优化了反应物、产物、中间体和过渡态的几何构型,并在UQCISD(T)／6—311 G(2df,2pO)水平上计算了单点能量．为了确证过渡态的真实性,在UB3LYP／6—311 G(3df,3pd)水平上进行了内禀坐标(IRC)计算和频率分析,并确定了反应机理．研究结果表明,反应主要产物为CH2CHO和Cl．     

A Theoretical Study on the Mechanism of C2H4 Oxidation over a Neutral V3O8 Cluster

Density functional theory (DFT) calculations are used to investigate the reaction mechanism of V₃O₈+C₂H₄. The reaction of V₃O₈ with C₂H₄ produces V₃O₇CH₂+HCHO or V₃O₇+CH₂OCH₂ overall barrierlessly at room temperature, whereas formation of hydrogen‐transfer products V₃O₇+CH₃CHO is subject to a tiny overall free energy barrier (0.03 eV), although the formation of the last‐named pair of products is thermodynamically more favorable than that of the first two. These DFT results are in agreement with recent experimental observations. The (O_b)₂V(O_tO_t)^. (b=bridging, t=terminal) moiety containing the oxygen radical in V₃O₈ is the active site in the reaction with C₂H₄. Similarities and differences between the reactivities of (O_b)₂V(O_tO_t)^. in V₃O₈ and the small VO₃ cluster [(O_t)₂VO_t^.] are discussed. Moreover, the effect of the support on the reactivity of the (O_b)₂V(O_tO_t)^. active site is evaluated by investigating the reactivity of the cluster VX₂O₈, which is obtained by replacing the V atoms in the (O_b)₃VO_t support moieties of V₃O₈ with X atoms (X=P, As, Sb, Nb, Ta, Si, and Ti). Support X atoms with different electronegativities influence the oxidative reactivity of the (O_b)₂V(O_tO_t)^. active site through changing the net charge of the active site. These theoretical predictions of the mechanism of V₃O₈+C₂H₄ and the effect of the support on the active site may be helpful for understanding the reactivity and selectivity of reactive O^. species over condensed‐phase catalysts.     

Theoretical study of the chemisorption of CO on Al2O3(0001)

Density functional molecular cluster calculations have been used to study the adsorption of CO on the alpha-Al2O3-(0001) surface. Substrate and adsorbate geometry modifications, adsorption enthalpies, and adsorbate vibrations are computed. Despite the rather small size of the employed cluster, relaxation phenomena evaluated for the clean surface agree well with experimental measurements and periodic slab calculations and mainly consist of an inward relaxation of the Lewis acid site (Lsa). Different adsorbate arrangements, perpendicular and parallel to the surface, have been considered. Among them, the most state CO chemisorption geometry (delta Hads approximately -13 kcal/mol) is that corresponding to the adsorbate perpendicular to the surface, atop Lsa and C-down oriented. The C-O stretching frequency (nu C-O) computed for such an arrangement is 2158 cm-1, i.e., blue shifted by 44 cm-1 with respect to the free adsorbate. The lack of experimental evidence pertaining to CO interacting with a well-defined alpha-Al2O3(0001) surface prevents the possibility of a direct check of the computed quantities. Nevertheless, low-temperature IR data for CO on alumina powders (Zecchina, A.; Escalona Platero, E.; Otero Areán, C. J. Catal. 1987, 107, 244) indicate for the chemisorbed species a delta nu = 12 cm-1. The adsorbate-substrate interaction relieves some of the Lsa relaxation, even if the Lsa electronic structure is only slightly affected upon chemisorption.     

Role of Hydrocarbon Radicals CHx (x=1, 2, 3) in Graphene Growth: A Theoretical Perspective

Many outstanding properties of graphene are blocked by the existence of structural defects. Herein, we propose an important healing mechanism for the growth of graphene, which is produced via plasma‐enhanced chemical vapor decomposition (PECVD), that is, the healing of graphene with single vacancies by decomposed CH₄ (hydrocarbon radical CH_x, x=1, 2, 3). The healing processes undergo three evolutionary steps: 1) the chemisorption of the hydrocarbon radicals, 2) the incorporation of the C atom of the hydrocarbon radicals into the defective graphene, accompanied by the adsorption of the leaving H atom on the graphene surface, 3) the removal of the adsorbed H atom and H₂ molecule to generate the perfect graphene. The overall healing processes are barrierless, with a huge released heat of 530.79, 290.67, and 159.04 kcal mol^?1, respectively, indicative of the easy healing of graphene with single vacancies by hydrocarbon radicals. Therefore, the good performance of the PECVD method for the generation of graphene might be ascribed to the dual role of the CH_x (x=1, 2, 3) species, acting both as carbon source and as defect healer.     

Theoretical study on the reaction mechanism of (CH3)3CO(.) radical with NO

The reaction mechanism of (CH3)3CO(.) radical with NO is theoretically investigated at the B3LYP/6-31G* level. The results show that the reaction is multi-channel in the single state and triplet state. The potential energy surfaces of reaction paths in the single state are lower than that in the triple state. The balance reaction: (CH3)3CONO←→ (CH3)3CO(.)+NO, whose potential energy surface is the lowest in all the reaction paths, makes the probability of measuring (CH3)3CO(.) radical increase. So NO may be considered as a stabilizing reagent for the (CH3)3CO(.)radical.