A quantum chemical study on the mechanism of the consecutive addition of HCN to propionitrile

MINDO/3 MO method has been used to study the mechanism of the consecutive addition of HCN to propionitrile. The results obtained for the first five steps show that the reaction is exothermic, and step 1 is the rate determining step.     

Quantum chemical study on the thermal Diels-Alder reaction of cyclohexadiene and methyl crotonate

AM1 molecular orbital method using the unrestricted Hartree-Fock(UHF) calculations has been applied to investigate the thermal reaction of cyclohexadiene and methyl crotonate. The calculated results indicate that the thermal Diels-Alder reaction proceeds to product through the concerted path and two radical pathways.     

A computational study of conformational interconversions in 1,4-dithiacyclohexane (1,4-dithiane)

Ab initio molecular orbital theory with the 6-31G(d), 6-31G(d,p), 6-31+G(d), 6-31+G(d,p), 6-31+G(2d,p), 6-311G(d), 6-311G(d,p), and 6-311+G(2d,p) basis sets and density functional theory (BLYP, B3LYP, B3P86, B3PW91) have been used to locate transition states involved in the conformational interconversions of 1,4-dithiacyclohexane (1,4-dithiane) and to calculate the geometry optimized structures, relative energies, enthalpies, entropies, and free energies of the chair and twist conformers. In the chair and 1,4-twist conformers the C-Hax and C-Heq bond lengths are equal at each carbon, which suggest an absence of stereoelectronic hyperconjugative interactions involving carbon-hydrogen bonds. The 1,4-boat transition state structure was 9.53 to 10.5 kcal/mol higher in energy than the chair conformer and 4.75 to 5.82 kcal/mol higher in energy than the 1,4-twist conformer. Intrinsic reaction coordinate (IRC) calculations showed that the 1,4-boat transition state structure was the energy maximum in the interconversion of the enantiomers of the 1,4-twist conformer. The energy difference between the chair conformer and the 1,4-twist conformer was 4.85 kcal/mol and the chair-1,4-twist free energy difference (deltaG degrees (c-t)) was 4.93 kcal/mol at 298.15 K. Intrinsic reaction coordinate (IRC) calculations connected the transition state between the chair conformer and the 1,4-twist conformer. This transition state is 11.7 kcal/mol higher in energy than the chair conformer. The effects of basis sets on the 1,4-dithiane calculations and the relative energies of saturated and unsaturated six-membered dithianes and dioxanes are also discussed.     

Theoretical study on the vibrational state distribution of product CO in the photolysis of acetoneCH_3 COCH_3 \underrightarrow {hv}2CH_3 + CO

The photolysis of acetone has been studied at 6-311G basis set using unrestricted Hartree-Fock method. The results show that ground state acetone (S_o) cannot easily dissociate. The electrons of acetone undergo n→II transition in laser, and excited acetone (T₁) can easily dissociate: and acetyl can further undergo themolytic dissociation: CH₃CO→CH₃+CO(R₂). The dynamic information (ω_k B _KF V₀(S)) of reaction R₂ is obtained and the vibrational state distributions of product CO are calculated. The calculated value consists with the experimental value. Project supported by the National Natural Science Foundation of China (Grant No. 29773007).     

丙烯醛光致脱羰机理的量子化学研究

用量子化学方法研究了丙烯醛基态和激发态的反应途径, 通过比较不同反应途径的反应势垒和中间产物构型的稳定性, 从理论上得出该反应的反应机理。     

低硝酸盐离子N2O22-和亚硝酸HONO的异构体及其异构化反应的量化研究

采用Gaussian-98程序进行，在HF／6—31G(d)，B3LYP／6—31G(d)和MP2／6—31G(d)水平下优化分子结构并寻找过渡态，对于MP2／6—31G(d)结果在QCISD(T，E4T)，MP4／6—311 G(d，p)，MP4／6—311 G(2df，p)水平下重新计算能级．并用内禀反应坐标(IRC)法研究了N2O2^2-和亚硝酸HONO的异构化反应机理。     

乙酰丙酮热分解反应的理论研究

用MINDO/3方法研究了乙酰丙酮的热分解反应，研究结果表明，醇式构型比酮式构型稳定；具有最低能垒的两个反应通道──反应(1)和(2)的活化位垒分别为210.250和225.501 kJ·mol~(-1)．     

鸟嘌呤受羟基自由基损伤反应机理的量子化学研究

用密度泛函理论(DFT)研究羟基自由基与鸟嘌呤分子加成反应的过渡态, 并进行内禀反应坐标(IRC)反应路径解析, 结果表明, 羟基自由基加成到鸟嘌呤碳碳双键上. 利用B3LYP/6-31++G**对反应物、反应物络合物、过渡态以及产物络合物等反应通道上各个能量驻点的能量进行了计算, 得到反应活化能E_a=28.0867 kJ/mol. AIM计算结果显示, 过渡态结构中鸟嘌呤分子碳碳双键结构被削弱, 羟基自由基氧原子与鸟嘌呤分子碳碳双键中的C4原子具有较强的相互作用, 双键中剩余的π电子离域到了环体系中.     

Calculation of the Canonical Rate Constant for the Nonadiabatic Trapping Model Based on Unified Statistical Theory:A Test on The Exchange Reaction H_2 H

IntroductionTheunifiedstatisticaltheory(UST)proposedbyMiller'isappropriatefordescribingdirectcomPlexreachonmechanismsand,especially,thenonadiabahctraPPingmodel.ThelatterisunrelatedtotheInindriaonthepotenhalenergysurface(PES),butrelatedtomulh-dividingsurfaces.ThedetenninahonofdividingsuifacescorrespondingtotherelahveInindriaorrelativemaxdriaofthefluxintegral(N(E,S))playsthecentralroleinUST.ThedividingsurfacesaregenerallyandrigorouslydefmedbyandcrocanonicalvariahonalmethodofN(E,S)onthee…     

Theoretical study on the vibrational state distribution of product CO in the photolysis of acetone CH_3COCH_3-→2CH_3 CO

The photolysis of acetone has been studied at 6-311G basis set using unrestricted Hartree-Fock method. The results show that ground state acetone (S_0) cannot easily dissociate. The electrons of acetone undergo n→Ⅱ transition in laser, and excited acetone (T_1) can easily dissociate: and acetyl can further undergo thermolytic dissociation: CH_3CO→CH_3 CO(R_2). The dynamic information (ω_K, B_(KF), V_0(S)) of reaction R_2 is obtained and the vibrational state distributions of product CO are calculated. The calculated value consists with the experimental value.     

Quantum chemical investigation on the reaction mechanism of tertiary phosphines with unsaturated carboxylic acids: An insight into kinetic data

The structures of intermediates and transition states in the reaction of tertiary phosphines with unsaturated carboxylic acids have been calculated at the B3LYP level of theory using the 6‐31+G(d,p) basis set. Analysis of the results shows that [1,3]‐intramolecular migration of carboxylic proton to carbanionic center of generated zwitterionic intermediate is strongly kinetically unfavorable, and external proton‐donor source is essential to complete quaternization. A molecular cluster of the intermediate with one molecule of water has been modeled for intermolecular reaction pathway, but even in this case, the proton transfer remains to be the rate‐determining step that is in a good agreement with previous kinetic investigations on this reaction. The data obtained for this reaction have much in common with recent studies on the mechanisms of the Morita–Baylis–Hillman reaction and phosphine‐catalyzed [3+2] cycloaddition, which revealed paramount importance of proton‐transfer steps. © 2013 Wiley Periodicals, Inc.     

N-取代乙基吡唑热消除反应的量子化学研究

用MINDO/3方法研究了N-取代乙基吡唑热消除反应H₃C₃N₂CH₂CH₂X→H₄C₃N₂+H₂C=CHX(反应Ⅰ～Ⅲ,对应X=H,CH₃,F)的机理,结果表明,甲基的超共轭效应以及F的强吸电子作用和邻基参与使得反应Ⅱ和反应Ⅲ的活化势垒降低,比反应Ⅰ更易进行。     

Quantum chemical studies on addition reactions of carbene with carbon monoxide and formaldehyde

MNDO method has been employed to study the reaction paths and to optimize the structures of the reactants, products and transition states of the addition reactions of carbene with carbon monoxide and formaldehyde available. Mechanisms have been obtained.     

A Computational Study of Chair–Twist Energy Differences and the Chair–Chair Conformational Interconversion in Tetrahydro-2H-thiopyran (Thiacyclohexane,Thiane)

Ab initio molecular orbital theory with the LANL2DZ, 3-21G, 6-31G(d), 6-31+G(d), 6-31+G(d,p), 6-311+G(d,p),6-31G(2d), 6-31G(3d), and 6-311G(d,p) basis sets and density functional theory (B3P86, B3LYP, B3PW91) have been used to calculate the structures, relative energies, enthalpies, entropies, and free energies of the chair, 1,4-twist, and 2,5-twist conformers of tetrahydro-2H-thiopyran (tetrahydrothiopyran, thiacyclohexane, thiane, pentamethylene sulfide). All levels of theory calculated similar energy values and the effect of basis sets on the calculated energies was small. The chair conformer of tetrahydro-2H-thiopyran was 5.27 kcal/mol more stable than the 1,4-twist conformer, which was slightly more stable (0.81 kcal/mol) than the 2,5-twist conformer. The chair–1,4-twist and chair–2,5-twist free energy differences ( G°_{c – t}) were 5.44 and 5.71 kcal/mol, respectively. Intrinsic reaction coordinate [IRC, minimum-energy path (MEP)] calculations connected the transition state between the chair and the 2,5-twist conformers. This transition state is 9.73 kcal/mol higher in energy than the chair conformer and the energy differences between the chair and the 1,4-boat and 2,5-boat transition states were 8.07 and 6.38 kcal/mol, respectively. Stereoelectronic hyperconjugative interactions were observed in the chair, 1,4-twist, and 2,5-twist conformers of tetrahydro-2H-thiopyran. The stereoelectronic hyperconjugative effects in the chair conformer of tetrahydro-2H-thiopyran have been compared to those in the respective chair conformers of tetrahydro-2H-pyran, tetrahydro-2H-selenane, and tetrahydro-2H-tellurane.     

Implementation and performance of the artificial force induced reaction method in the GRRM17 program

This article reports implementation and performance of the artificial force induced reaction (AFIR) method in the upcoming 2017 version of GRRM program (GRRM17). The AFIR method, which is one of automated reaction path search methods, induces geometrical deformations in a system by pushing or pulling fragments defined in the system by an artificial force. In GRRM17, three different algorithms, that is, multicomponent algorithm (MC‐AFIR), single‐component algorithm (SC‐AFIR), and double‐sphere algorithm (DS‐AFIR), are available, where the MC‐AFIR was the only algorithm which has been available in the previous 2014 version. The MC‐AFIR does automated sampling of reaction pathways between two or more reactant molecules. The SC‐AFIR performs automated generation of global or semiglobal reaction path network. The DS‐AFIR finds a single path between given two structures. Exploration of minimum energy structures within the hypersurface in which two different electronic states degenerate, and an interface with the quantum mechanics/molecular mechanics method, are also described. A code termed SAFIRE will also be available, as a visualization software for complicated reaction path networks. © 2017 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.     

Mechanism and structural aspects of thermal Curtius rearrangement. Quantum chemical study

The electronic and geometric structures of formyl, acetyl, and benzoyl azides were studied and fragments of the potential surfaces for the thermal Curtius rearrangement of these azides into the corresponding isocyanates were calculated by density functional theory at the PBE/TZ2P level. Acyl azides adopt two stable, conformations syn and anti, with respect to the C-N bond. The syn conformers are more stable than their anti analogs. The activation energies of the syn-anti isomerization in the series under study are 9.4, 7.0, and 9.2 kcal mol⁻¹, respectively, and the activation energies of the reverse reaction are 8.5, 6.1, and 2.5 kcal mol⁻¹. The rearrangement of syn-acyl azides is a one-step process, in which elimination of N₂ occurs synchronously with the rearrangement of atoms and bonds to form isocyanates. The activation energies of the rearrangements of syn-HC(O)N₃, syn-MeC(O)N₃, and syn-PhC(O)N₃ are 28.0, 32.9, and 34.5 kcal mol⁻¹, respectively. The rearrangement of the anti conformers of the above-mentioned azides involves the formation of singlet acylnitrene. The activation energies of the latter process are 34.6, 32.9, and 32.3 kcal mol⁻¹, respectively. The activation energies of the rearrangement of acylnitrenes into isocyanates are 20.9, 18.9, and 13.6 kcal mol⁻¹, respectively. The energy characteristics of the process and the structural data for the starting compounds, final products, and transition states provide evidence that the thermal Curtius rearrangement occurs predominantly by a concerted mechanism. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2200–2209, October, 2005.     

MIVDO/3方法研究RC(X)OC(O)CH3热分解反应

用ＭＩＮＤＯ／３方法研究了酸酐（Ｘ＝Ｏ）和硫代酸酐（Ｘ＝Ｓ）的热分解反应。结果表明，含有β－氢原子的乙酸酐和硫代乙酸酐可按三条路径分解，苯基对热分解的影响不大。     

Novel variational principles of chemical reaction

Minimum principles of chemical reaction coordinates are established. IRC (intrinsic reaction coordinate) draws the path of minimum distance from reactant to product. The distance is measured in the rigged configuration Riemannian space whose metric is determined by the distribution of the adiabatic potential energy. Moreover, minimum property of the intrinsic principle of least action is established for the intrinsic dynamism of chemical reaction. Minimum principle of the path connecting intercell boundary with cell is also discussed.     

F-N=C→F-C≡N的动力学及产物的振动态分布

用数值方案，在RHF／3－21G分子轨道从头算法的水平上，得到了氟化异氰FNC到氟化氰FCN重排反应的反应途径（内禀反应坐标IRC）．沿着IRC；讨论了反应过程中体系几何构型的变化，计算了沿IRC运动与垂直于IRC简正振动之间的耦合常数（BK，F），各振动模式对应的频率（ωK），使用统一的半经典徽扰和无限级突然（SCP－IOS）近似理论计算了在一定能量下产物的振动分配.结果表明，在过渡态后，耦合常数（BK,F）的大小强烈地影响产物的振动态分布,另外用传统过渡态、变分过渡态理论及相关的隧道效应校正计算了该反应的速率常数.