Theoretical study on the gas phase reaction of acrylonitrile with a hydroxyl radical

The mechanism and kinetics of the reaction of acrylonitrile (CH(2)=CHCN) with hydroxyl (OH) has been investigated theoretically. This reaction is revealed to be one of the most significant loss processes of acrylonitrile. BHandHLYP and M05-2X methods are employed to obtain initial geometries. The reaction mechanism conforms that OH addition to C[double bond, length as m-dash]C double bond or C atom of -CN group to form the chemically activated adducts, 1-IM1(HOCH(2)=CHCN), 2-IM1(CH(2)=HOCHCN), and 3-IM1(CH(2)=CHCOHN) via low barriers, and direct hydrogen abstraction paths may also occur. Temperature- and pressure-dependent rate constants have been evaluated using the Rice-Ramsperger-Kassel-Marcus theory. The calculated rate constants are in good agreement with the experimental data. At atmospheric pressure with N(2) as bath gas, 1-IM1(OHCH(2)=CHCN) formed by collisional stabilization is the major product in the temperature range of 200-1200 K. The production of CH(2)CCN and CHCHCN via hydrogen abstractions becomes dominant at high temperatures (1200-3000 K).     

Theoretical study on the reaction mechanism of CN radical with ketene

The bimolecular single collision reaction potential energy surface of CN radical with ketene (CH2CO) was investigated by means of B3LYP and QCISD(T) methods. The calculated results indicate that there are three possible channels in the reaction. The first is an attack reaction by the carbon atom of CN at the carbon atom of the methylene of CH2CO to form the intermediate NCCH2CO followed by a rupture reaction of the C-C bond combined with -CO group to the products CH2CN CO. The second is a direct addition reaction between CN and CH2CO to form the intermediate CH2C(O)CN followed by its isomerization into NCCH2CO via a CN-shift reaction, and subsequently, NCCH2CO dissociates into CH2CN CO through a CO-loss reaction. The last is a direct hydrogen abstraction reaction of CH2CO by CN radical. Because of the existence of a 15.44 kJ/mol reaction barrier and higher energy of reaction products, the path can be ruled out as an important channel in the reaction kinetics. The present theoretical computation results, which give an available suggestion on the reaction mechanism, are in good agreement with previous experimental studies.     

Theoretical investigation on the mechanism and kinetics of OH radical with ethylbenzene

The OH hydrogen abstraction and addition with ethylbenzene have been studied in the range 298–1000 K using quantum chemistry methods. The geometries and frequencies of the reactants, transition states, and products were performed at BH and HLYP/6‐311++G(d,p) level, single point calculation for all the stationary points were carried out at CCSD(T) calculations of the optimized structures with the same basis set. Nine different reaction paths are considered corresponding to two side chain, three possible ring hydrogen abstraction, and four kinds different OH addition. The results of the theoretical study indicate that at the room temperature the reaction proceeds almost exclusively through OH addition, and is predicted to occur dominantly at the ortho position, the calculated overall rate constant is 6.72 × 10^?12 cm³ molecule^?1 s^?1, showing a very good agreement with available experimental data. Although negligible at low temperature, at 1000 K ring hydrogen abstraction accounts for about 32% of the total abstraction reaction, and the whole hydrogen abstraction makes up for 30% of the total reaction. This study may provide useful information on understanding the mechanistic features of OH‐initiated oxidation of ethylbenzene. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical mechanistic study on the reaction of CN radical with HNCN

The mechanism for the reaction of the cyanogen radical (CN) with the cyanomidyl radical (HNCN) has been investigated theoretically. The electronic structure information of the singlet and triplet potential energy surfaces (PESs) is obtained at the B3LYP/6-311+G(3df,2p) level, and the single-point energies are refined at the CCSD(T)/6-311+G(3df,2p) level as well as by multilevel MCG3-MPWB method. The calculations show that the C atom of CN additions to middle- and end-N atoms of HNCN are two barrierless association processes leading to the energy-rich intermediates IM1 HN(CN)CN and IM2 HNCNCN, respectively, on the singlet PES. The higher barriers of the subsequent isomerization and dissociation channels from IM1 and IM2 indicate that these two intermediates, which have considerably thermodynamic and kinetic stability, are the dominant product at high pressure. While at low pressure, the most favorable product is P(2) H + NCNCN, which will be formed from both IM1 and IM2 via direct dissociation processes by the H-N bond rupture, and the secondary feasible product is P(4) HCN + (1) NCN, while P(5) HCCN + N(2) and P(6) HCNC + N(2) are the least competitive products. On the triplet PES, P(14) NCNC + HN may be a comparable competitive product at high temperature. In addition, the comparison between the mechanisms of the CN + HNCN and OH + HNCN reactions is made. The present results will enrich our understanding of the chemistry of the HNCN radical in combustion processes and interstellar space.     

Theoretical and experimental interpretations of phenol oxidation by the hydroxyl radical

Phenol oxidation by OH radicals produced by the Fenton reaction was studied and the oxidation process was monitored by the UV–visible, ¹³C NMR and LC techniques. The results show that benzoquinone is formed. In the NMR and LC experiments, since the peaks corresponding to isomers ortho and para- benzoquinones are unresolved, DFT was used to determine the branching ratios of the isomers formation that coincides with their ΔG values (ortho > para > meta): 72% for ortho, 23% for para and 5.0% for meta. Furthermore, the energy profile of the OH attack at ortho is quite similar to that at the para position while the meta position attack is less favored by 2.0 kcal/mol.     

Theoretical study on the atmospheric reaction of CH3O2 with OH

A quantum chemical investigation on the reaction mechanism of CH₃O₂ with OH has been performed. Based on B3LYP and QCISD(T) calculations, seven possible singlet pathways and seven possible triplet pathways have been found. On the singlet potential energy surface (PES), the most favorable channel starts with a barrierless addition of O atom to CH₃O₂ leading to CH₃OOOH and then the O? O bond dissociates to give out CH₃O + HO₂. On the triplet PES, the calculations indicate that the dominant products should be ³CH₂O₂ + H₂O with an energy barrier of 29.95 kJ/mol. The results obtained in this work enrich the theoretical information of the title reaction and provide guidance for analogous atmospheric chemistry reactions. © 2015 Wiley Periodicals, Inc.     

CH3SS与OH自由基反应机理的理论研究

应用密度泛函理论(DFT)对CH3SS与OH自由基单重态反应机理进行了研究.在B3PW91/6-311+G(d,p)水平上优化了反应通道上各驻点(反应物、中间体、过渡态和产物)的几何构型,用内禀反应坐标(IRC)计算和频率分析方法对过渡态进行了验证.在QCISD(T)/6-311++G(d,p)水平上计算了各物种的单点能,并对总能量进行了零点能校正.研究结果表明,CH3SS与OH反应为多通道反应,有5条可能的反应通道.反应物首先通过不同的S—O键相互作用形成具有竞争反应机理的中间体IM1和IM2.再经过氢迁移、脱氢和裂解等机理得到主要产物P1(CH2SS+H2O),次要产物P2(CH2S+HSOH),P3(CH3SH+1SO)和P4(CH2SSO+H2),其中最低反应通道的势垒为174.6kJ.mol-1.     

Theoretical study on the reaction of SiH(CH(3))(3) with SiH(3) radical

The multiple-channel reactions SiH(3) + SiH(CH(3))(3) --> products are investigated by direct dynamics method. The minimum energy path (MEP) is calculated at the MP2/6-31+G(d,p) level, and energetic information is further refined by the MC-QCISD (single-point) method. The rate constants for individual reaction channels are calculated by the improved canonical variational transition state theory with small-curvature tunneling correction over the temperature range of 200-2400 K. The theoretical three-parameter expression k(T) = 2.44 x 10(-23)T(3.94) exp(-4309.55/T) cm(3)/(molecule s) is given. Our calculations indicate that hydrogen abstraction channel R1 from SiH group is the major channel because of the smaller barrier height among five channels considered.     

Ab initio study of C4H3 potential energy surface and reaction of ground‐state carbon atom with propargyl radical

The potential energy surface for the reaction of the ground‐state carbon atom [C(³P_j)] with the propargyl radical [HCCCH₂(X²B₁)] is investigated using the G2M(RCC,MP2) method. Numerous local minima and transition states for various isomerization and dissociation pathways of doublet C₄H₃ are studied. The results show that C(³P_j) attacks the π system of the propargyl radical at the acetylenic carbon atom and yields the n‐C₄H₃(²A′) isomer i3 after an 1,2‐H atom shift. This intermediate either splits a hydrogen atom and produces singlet diacetylene, [HCCCCH ( p1 )+H] or undergoes (to a minor amount) a 1,2‐H migration to i‐C₄H₃(²A′) i5 , which in turn dissociates to p1 plus an H atom. Alternatively, atomic carbon adds to the triple C?C bond of the propargyl radical to form a three‐member ring C₄H₃ isomer i1 , which ring opens to i3 . Diacetylene is concluded to be a nearly exclusive product of the C(³P_j)+HCCCH₂ reaction. At the internal energy of 10.0 kcal/mol above the reactant level, Rice–Ramsperger–Kassel–Marcus calculations show about 91.7% of HCCCCH comes from fragmentation of i3 and 8.3% from i5 . The other possible minor channels are identified as HCCCC+H₂ and C₂H+HCCH. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1522–1535, 2001     

Theoretical study on reaction mechanism of the CF radical with nitrogen dioxide

The singlet potential energy surface of the [CFNO₂] system is investigated at the B3LYP and CCSD(T) (single‐point) levels to explore the possible reaction mechanism of CF radical with NO₂. The top attack of C‐atom of CF radical at the N‐atom of NO₂ molecule first forms the adduct isomer FCNO₂ 1 followed by oxygen‐shift to give trans‐OC(F)NO 2 and then to cis‐OC(F)NO 3 . Subsequently, the most favorable channel is a direct dissociation of 2 and 3 to product P₁ FCO+NO. The second and third less favorable channels are direct dissociation of 3 to product P₂ FNO+CO and isomerization of 3 to a complex NOF?CO 4 , which can easily dissociate to product P₃ FON+CO, respectively. The large exothermicity released in these processes further drives most of the three products P₁ , P₂ , and P₃ to take secondary dissociation to the final product P₁₂ F+CO+NO. Another energetically allowed channel is formation of product P₄ ¹NF+CO₂, yet it is much less competitive than P₁ , P₂ , P₃ , and P₁₂ . The present calculations can well interpret one recent experimental fact that the title reaction is quite fast yet still much slower than the analogous reaction CH+NO₂. Also, the results presented in this article may be useful for future product distribution analysis of the title reaction as well as for the analogous CCl and CBr reactions. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1907–1919, 2001     

Theoretical study on reaction mechanism of isocyanate radical NCO with ethene

The NCO + C₂H₄ reaction is simple and prototype for reaction of the NCO radical with unsaturated hydrocarbons, and it is considered to be important in fuel‐rich combustion. In this article, we for the first time perform detailed theoretical investigations for its reaction mechanism based on Gaussian‐3//B3LYP scheme covering various entrance and decomposition channels. The most favorable channel is firstly the NCO and C₂H₄ approach each other, forming a weakly‐bound complex L1 OCN···C₂H₄, followed by the formation of isomer L2 OCNCH₂CH₂ via a small barrier of 1.3 kcal/mol. Transition states of any decomposable or isomeric channels for L2 in energy are much higher than reactants, which indicate that adduct L2 has stabilization effect in this NCO + C₂H₄ reaction. The direct H‐abstraction channel leading to P1 HNCO + C₂H₃, might have an important contribution to the eventual products in high temperature. These results can well explain available kinetic experiment. Moreover, reaction mechanism for the title reaction is significantly different from the NCO + C₂H₂ reaction which proceeds on most favorably to generate the products HCN + HCCO and OCCHCN + H via a four‐membered ring intermediate. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

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.     

Mechanism and kinetics of the reaction of the 2-propargyl radical with ammonia

Gas-phase mechanism and kinetics of the reactions of the 2-propargyl radical (H₂CCCH), an important intermediate in combustion processes, with ammonia were investigated using ab initio molecular orbital theory at the coupled-cluster CCSD(T)//B3LYP/6-311++G(3df,2p) method in conjunction with transition state theory (TST), variational transition state theory (VTST), and Rice–Ramsperger–Kassel–Macus (RRKM) calculations for rate constants. The potential energy surface (PES) constructed shows that the C₃H₃ + NH₃ reaction has four main entrances, including two H-abstraction and two addition channels in which the former are energetically more favorable. The H-abstraction channels occur via energy barriers of 24 (T0/P2) and 26 kcal/mol (T0/P3) forming loose van de Waals complexes, COM_1 (12 kcal/mol) and COM_2 (14 kcal/mol), respectively. These complexes can easily be decomposed via barrier-less processes resulting HCCCH₃ + NH₂ (P2, 14 kcal/mol) and HCCCH₃ + NH₂ (P3, 15 kcal/mol), respectively. The additional channels occur initially by formation of two intermediate states, H₂CCCHNH₃ (35 kcal/mol) and H₂CC(NH₃)CH (37 kcal/mol) via energy barriers of 37 and 40 kcal/mol at T0/1 and T0/5, respectively, followed by isomerization and decomposition yielding 21 different products. These processes are fully depicted in an as-complete-as-possible PES. The rate constants and product branching ratios for the low-energy channels calculated show that the C₃H₃ + NH₃ reaction is almost pressure-independent. For the temperature range of 300–2000 K, the HCCCH₃ + NH₂ is the major product, whereas the minor one, HCCCH₃ + NH₂, has more contribution when temperature increases. Theoretical results on the mechanism and kinetics of the reaction considered may be helpful for future experiments as well as for understanding the role of the propargyl radical in combustion chemistry.     

A DFT study on reaction of eupatilin with hydroxyl radical in solution

Antioxidants scavenge reactive oxygen species and, therefore, are vitally important in the living cells. The antioxidant properties of eupatilin have recently been reported. In this article, the reactions of eupatilin with the hydroxyl radical (OH^?) in solution are studied using density functional theory calculations and the polarizable continuum model. Three mechanisms are considered including: sequential electron proton transfer (SEPT), sequential proton loss electron transfer (SPLET), and hydrogen abstraction (HA). Three solvents with different polarities, that is, benzene, methanol, and water, are used to investigate the effect of the environment on the mechanisms. The relative Gibbs free energies and enthalpies corresponding to different mechanisms are calculated. Our results show that SEPT is thermodynamically favored in aqueous solution. Once the eupatilin anion is produced, the second step in SPLET mechanism is thermodynamically favored in methanol and water. The HA mechanism is thermodynamically favored in gas, benzene, methanol, and water. This mechanism is more energetically favorable to occur in a more polar solvent. The natural bond orbital charges and spin densities as well as the singly occupied molecular orbital are then analyzed. It is concluded that the HA process is governed by proton coupled electron transfer mechanism. The attack of the radical takes place preferentially at position 7 of eupatilin. © 2012 Wiley Periodicals, Inc.     

Theoretical study of reaction of trifluoromethyl radical with hydroxyl and hydrogen radicals

Ab initio molecular orbital theory and density functional theory calculations have been carried out on the reactions of the trifluoromethyl radical with the hydroxyl and the hydrogen radicals. These reactions are key reactions that underlie a new fire extinguishing mechanism of non-bromine-containing halon replacements. The activation energies calculated by the MP2 and QCISD methods are in good agreement with the experimental values. The B3LYP, as well as MP2 and QCISD, give good results for the calculations of the heats of reactions. The GAUSSIAN-1 and GAUSSIAN-2 theory calculations present the most acxcurate results on both the activation energies and the heats of reactions. The effects of the scaling factors on the activation energies and the heats of reactions are also evaluated. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 277–289, 1998     

CH3+HNCO反应机理的理论研究

异氰酸(HNCO)分解引发的一系列自由基反应是氮氧化物快速消除机理[1,2](RAPRENOX)所研究的领域,该反应涉及到燃烧化学中氮氧化物NOX的消除,所以获得这些反应准确的位垒就成为实验化学和理论化学所要解决的问题。本文中我们重点研究CH3+HNCO反应机理,探讨CH3自由基是否也能象氮氢自由基一样,在异氰酸(HNCO)分解反应中起作用。1　计算方法用量子化学MP2方法,在6 311++G 水平上计算了CH3自由基与HNCO反应的反应物、产物、中间体和过渡态的几何构型,用QCISD(T)方法在6 311++G 水平上计算了它们的能量。通过振动分析确定…     

Theoretical studies on the reaction mechanism of CH2CH radical with HNCO

The reaction mechanism of CH₂CH radical with HNCO has been investigated systematically by density functional theory (DFT). The geometries and harmonic frequencies of reactants, intermediates, transition states, and products have been optimized with the B3LYP at different levels. At the same time, AIM is performed to calculate the charge density of some bonding critical points and the charges of some atoms. Nine feasible reaction pathways have been investigated. The results indicated that the main pathway is CH₂CH + HNCO → IMA1 → TSA1 → CH₂CH₂ + NCO, which is characterized by hydrogen atom transferring. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Lead-promoted Barbier-type reaction of aldehydes with propargyl bromides in aqueous media

This paper reports that the reaction of the propargyl bromides with aldehydes promoted by powdered lead in aqueous media.The selectivity and possible mechanism of these reactions are discussed.The yields of products for reaction of propargyl bromide are 31~71%.The ratios of al-lenyl alcohol and homopropargyl alcohol are 1:1.5 to 1:3.The product for reaction of phenyl propargyl bromide is allenyl alcohol and the yields are 52~84%.     

掺杂聚丙炔醇的电性能和表征

聚丙炔醇（ＰＯＨＰ）经碘、硫酸、三氯化铁、盐酸掺杂，其电导率可提高六个数量级，硫酸、三氯化铁、盐酸掺杂ＰＯＨＰ都显示良好的稳定性。通过红外光谱、光电子能谱、顺磁共振的研究。对掺杂ＰＯＨＰ的电荷转移过程及可能存在的栽流子进行了研究。     

CH3S与CO反应机理的理论研究

在G3(MP2)//B3LYP/6-311 G(d,p)水平上,对CH3S自由基与CO气相反应的微观机理进行了理论研究.结果表明:该反应共存在3个反应通道,产物分别为CH3 OCS,CH2S HCO和CH2S HOC.由于形成产物CH3 OCS的活化势垒较低,因此为主要反应通道,这与实验观察到的结果是一致的.