Theoretical study on the reaction mechanism of(CH_3)_3CO+CO

The global environment pollution includes pho-tochemical smog, acid rain and stratospheric ozonedepletion. The short-lived species/radicals in atmos-phere are closely related to these phenomena. Theshort-lived species/radicals bring the photochemicalsmog,…     

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.     

Theoretical study of stabling function of the NO to the (CH3)3CO · radical

The stabling function of the NO to the (CH₃)₃CO · radical has been theoretically investigated. Density functional theory (DFT) calculations are performed to optimize the geometries of relevant species. The single‐point energy is evaluated at CCSD(T)/6‐31++G** level. Three reaction channels of (CH₃)₃CO · + NO in the singlet state are considered. The calculations indicate that NO is a stable reagent of active radical (CH₃)₃CO. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Theoretical study on the mechanism of the (3)CH(2) + NO(2) reaction

The complex doublet potential energy surface of the CH(2)NO(2) system is investigated at the B3LYP/6-31G(d,p) and QCISD(T)/6-311G(d,p) (single-point) levels to explore the possible reaction mechanism of the triplet CH(2) radical with NO(2). Forty minimum isomers and 92 transition states are located. For the most relevant reaction pathways, the high-level QCISD(T)/6-311 + G(2df,2p) calculations are performed at the B3LYP/6-31G(d,p) geometries to accurately determine the energetics. It is found that the top attack of the (3)CH(2) radical at the N-atom of NO(2) first forms the branched open-chain H(2)CNO(2) a with no barrier followed by ring closure to give the three-membered ring isomer cC(H(2))ON-O b that will almost barrierlessly dissociate to product P(1) H(2)CO + NO. The lesser followed competitive channel is the 1,3-H-shift of a to isomer HCN(O)OH c, which will take subsequent cis-trans conversion and dissociation to P(2) OH + HCNO. The direct O-extrusion of a to product P(3) (3)O + H(2)CNO is even much less feasible. Because the intermediates and transition states involved in the above three channels are all lower than the reactants in energy, the title reaction is expected to be rapid, as is consistent with the measured large rate constant at room temperature. Formation of the other very low-lying dissociation products such as NH(2) + CO(2), OH + HNCO and H(2)O + NCO seems unlikely due to kinetic hindrance. Moreover, the (3)CH(2) attack at the end-O of NO(2) is a barrier-consumed process, and thus may only be of significance at very high temperatures. The reaction of the singlet CH(2) with NO(2) is also briefly discussed. Our calculated results may assist in future laboratory identification of the products of the title reaction.     

Theoretical Studies on Reaction Mechanism of CH3SO with NO

The potential energy surface （PES） of CH3SO radical with NO reaction has been studied at MP2/6-311G（2df, p） and QCISD/6-311G（2df, p） levels. Geometries of the reactants, transition states （TS） and products were optimized at B3LYP/6-311G （d,p） level. The geometries of the transition states were found for the first time. The calculated results show that the reaction can proceed via singlet-state or triplet-state PES. Because of the high energy barrier of triplet surface, the singlet surface reactions are dominant. The topological analysis of electron density shows that there are two kinds of structaral transition states （the bifurcation-type ring structure transition state and the T-shaped conflict structure transition state） in the titled reaction. The total electronic density of the reactants, TS and products and the spin electronic density on the triplet surface were also discussed in this paper.     

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 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     

Theoretical study on the mechanism of the CH2F + NO2 reaction

Despite the importance of the Fluoromethyl radicals in combustion chemistry, very little experimental information on their reactions toward stable molecules is available in the literature. Motivated by recent laboratory characterization about the reaction kinetics of Chloromethyl radicals with NO2, we carried out a detailed potential energy survey on the CH2F + NO2 reaction at the B3LYP/6-311G(d,p) and MC-QCISD (single-point) levels as an attempt toward understanding the CH2F + NO2 reaction mechanism. It is shown that the CH2F radical can react with NO2 to barrierlessly generate adduct a (H2FCNO2), followed by isomerization to b1 (H2FCONO-trans) which can easily interconvert to b2 (H2FCONO-cis). Subsequently, Starting from b (b1, b2), the most feasible pathway is the C--F and N--O1 bonds cleavage along with N--F bond formation of b (b1, b2) leading to P1 (CH2O + FNO), or the direct N--O1 weak-bond fission of b (b1, b2) to give P2 (CH2FO + NO), or the 1,3-H-shift associated with N--O1 bond rupture of b1 to form P3 (CHFO + HNO), all of which may have comparable contribution to the reaction CH2F + NO2. Much less competitively, b2 either take the 1,4-H-shift and O1--N bond cleavage to form product P4 (CHFO + HON) or undergo a concerted H-shift to isomer c2 (HFCONOH), followed by dissociation to P4. Because the rate-determining transition state (TSab1) in the most competitive channels is only 0.3 kcal/mol higher than the reactants in energy, the CH2F + NO2 reaction is expected to be rapid, and may thus be expected to significantly contribute to elimination of nitrogen dioxide pollutants. The similarities and discrepancies among the CH2X + NO2 (X = H, F, and Cl) reactions are discussed in terms of the electronegativity of halogen atom. The present article may assist in future experimental identification of the product distributions for the title reaction, and may be helpful for understanding the halogenated methyl chemistry.     

Theoretical study of the mechanism of CH2CO + CN reaction

The potential energy surface information of the CH₂CO + CN reaction is obtained at the B3LYP/6‐311+G(d,p) level. To gain further mechanistic knowledge, higher‐level single‐point calculations for the stationary points are performed at the QCISD(T)/6‐311++G(d,p) level. The CH₂CO + CN reaction proceeds through four possible mechanisms: direct hydrogen abstraction, olefinic carbon addition–elimination, carbonyl carbon addition–elimination, and side oxygen addition–elimination. Our calculations demonstrate that R→IM1→TS3→P3: CH₂CN + CO is the energetically favorable channel; however, channel R→IM2→TS4→P4: CH₂NC + CO is considerably competitive, especially as the temperature increases (R, IM, TS, and P represent reactant, intermediate, transition state, and product, respectively). The present study may be helpful in probing the mechanism of the CH₂CO + CN reaction. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

DFT investigation of the mechanism of CH2CO + O(3P) reaction

A detailed theoretical survey of the potential energy surface (PES) for the CH₂CO + O(³P) reaction is carried out at the QCISD(T)/6‐311+G(3df,2p)//B3LYP/6‐311+G(d,p) level. The geometries, vibrational frequencies, and energies of all stationary points involved in the reaction are calculated at the B3LYP/6‐311+G(d,p) level. More accurate energy information is provided by single‐point calculations at the QCISD(T)/6‐311+G(3df,2p) level. Relationships of the reactants, transition states, intermediates, and products are confirmed by the intrinsic reaction coordinate (IRC) calculations. The results suggest that P1(CH₂+CO₂) is the most important product. This study presents highlights of the mechanism of the title reaction. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

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.     

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 Studies of the Reaction Mechanisms of CH3S＋NO2

The potential energy surface for the CH3S NO2 reaction has been studied using the ab initio G3(MP2) method. A variety of possible complexes and saddle points along the minimum energy reaction paths have been characterized at UMP2 (full)/6-31G(d) level. The calculations reveal dominating reaction mechanisms of the title reaction: CH3S NO2 firstly produce intermediate CH3SONO,then break up into CH3SO NO. The results are valuable to understand the atmospheric sulfur compounds oxidation mechanism.     

Theoretical study on the reaction mechanism of the methyl radical with nitrogen oxides

The radical-molecule reaction mechanism of CH3 with NOx (x = 1, 2) has been explored theoretically at the B3LYP/6-311Gd,p and MC-QCISD (single-point) levels of theory. For the singlet potential energy surface (PES) of the CH3 + NO2 reaction, it is found that the carbon to middle nitrogen attack between CH3 and NO2 can form energy-rich adduct a (H3CNO2) with no barrier followed by isomerization to b1 (CH3ONO-trans), which can easily convert to b2 (CH3ONO-cis). Subsequently, starting from b (b1, b2), the most feasible pathway is the direct N-O bond cleavage of b (b1, b2) leading to P1 (CH3O + NO) or the 1,3-H-shift and N-O bond rupture of b1 to form P2 (CH2O + HNO), both of which may have comparable contribution to the reaction CH3 + NO2. Much less competitively, b2 can take a concerted H-shift and N-O bond cleavage to form product P3 (CH2O + HON). Because the intermediates and transition states involved in the above three channels are all lower than the reactants in energy, the CH3 + NO2 reaction is expected to be rapid, as is consistent with the experimental measurement in quality. For the singlet PES of the CH3 + NO reaction, the major product is found to be P1 (HCN + H2O), whereas the minor products are P2 (HNCO + H2) and P3 (HNC +H2O). The CH3 + NO reaction is predicted to be only of significance at high temperatures because the transition states involved in the most feasible pathways lie almost above the reactants. Compared with the singlet pathways, the triplet pathways may have less contributions to both reactions. The present study may be helpful for further experimental investigation of the title reactions.     

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 study on reaction mechanism of the fluoromethylene radical with nitrogen dioxide

The complex doublet potential energy surface for the reaction of 1CHF with NO2, including 14 minimum isomers and 30 transition states, is explored theoretically at the B3LYP/6-311G(d,p) and CCSD(T)/6-311G(d,p) (single-point) levels of theory. The initial association between 1CHF and NO2 is found to be the carbon-to-middle-nitrogen attack forming an energy-rich adduct a (HFCNO2) with no barrier, followed by concerted O-shift and C--N bond rupture leading to product P2 (NO + HFCO), which is the most abundant. In addition, a can take a 1,3-H-shift to isomer b (FCN(O)OH) followed by the dissociation to form the second feasible product P4 (OH + FCNO). The least favorable pathway is that b undergoes a concerted OH-shift to form d (HO(F)CNO), which will dissociate to product P5 (HF+OCNO) via side HF-elimination. The secondary dissociation of P5 may form product P7 (HF+NO+CO) easily. Furthermore, the 1CHF attack at the end-O of NO2 is a barrier-consumed process, and thus may only be of significance at high temperatures. The comparison with the analogous reactions 1CHCl + NO2 is discussed. The present study may be helpful for probing the mechanism of the title reaction and understanding the halogenated carbine chemistry.     

1-氟-1,1- 二氯乙烷与氟原子反应的理论研究

利用密度泛函理论研究了CH3CCl2F与F原子的反应机理.在MPW1K水平下计算了反应物、过渡态和产物的几何构型和频率,并进一步利用内禀反应坐标理论获得了反应的最小能量路径;在G3(MP2)水平下对所有驻点进行了单点能量校正.结果表明,CH3CCl2F与F原子的反应存在两个H迁移反应通道:CH2H′CCl 2F+F→C...     

Computational study of the reaction of the methylsulfonyl radical,CH3S(O)2, with NO2

The mechanism of the reaction between the methylsulfonyl radical, CH₃S(O)₂, and NO₂ is examined using density functional theory and ab initio calculations. Two stable association intermediates, CH₃SNO₂ and CH₃S(O)ONO, may be formed through the attack of the nitrogen or the oxygen atom of NO₂ radical to the S atom. Interisomerization and decomposition of these intermediates are investigated using high level energy methods and specifically, CCSD(T), CBS‐QB3, and G3//B3LYP. The computational investigation indicates that the lowest energy reaction pathway leads to the products CH₃S(O)₃ + NO, through the decomposition of the most stable association adduct CH₃S(O)ONO. This result fully supports the relevant assumption of Ray et al. (Ray et al., J. Phys. Chem. 1996, 100, 8895], on which the experimental evaluation of the rate constant was based, namely that CH₃S(O)₃ + NO are the most probable products of the reaction CH₃S(O)₂ + NO₂. © 2014 Wiley Periodicals, Inc.     

Theoretical study on the mechanism of the 1CHCl + NO reaction

The complex doublet potential energy surface of the CHClNO system, including 31 minimum isomers and 84 transition states, is investigated at the QCISD(T)/6-311G(d, p)//B3LYP/6-31G(d, p) level in order to explore the possible reaction mechanism of the singlet CHCl with NO. Various possible isomerization and dissociation channels are probed. The initial association between 1CHCl and NO at the terminal N-site can almost barrierlessly lead to the chainlike adducts HClCNO a (a1, a2) followed by the direct Cl-extrusion to product P9 Cl + HCNO, which is the most feasible channel. Much less competitively, a (a1, a2) undergoes a ring-closure leading to the cyclic isomer c-C(HCl)NO d followed by a concerted Cl-shift and N-O cleavage of d to form the branched isomers ClNC(H)O f (f1, f2). Eventually, f (f1, f2) may take a direct H-extrusion to produce P7 H + ClNCO or a concerted 1,2-H-shift and Cl-extrusion to form P1 Cl + HNCO. The low-lying products P2 HCl + NCO, P3 Cl + HOCN, P14 HCO + 3NCl, P6 ClO + HCN, and P13 ClNC + OH may have the lowest yields observed. Our calculations show that the product distributions of the title reaction are quite different from those of the analogous 1CHF + NO reaction, yet are similar to those of another analogous 3CH2 + NO reaction. The similarities and discrepancies among the three reactions are discussed in terms of the substitution effect. The present article may assist in future experimental identification of the product distributions for the title reaction and may be helpful for understanding the halogenated carbene chemistry.     

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.