NH_2(~2B_1)与CH_4反应机理的理论研究

在密度泛函理论 B3LYP/6 -31 1 G*水平下 ,研究了 NH2 与 CH4的反应机理 .通过振动频率和内禀反应坐标 ( IRC)分析 ,对反应过渡态进行了确认 .在 QCISD( T) /6 -31 1 G*水平下进行了单点能计算 ,并进行了零点能校正 ,结果表明 ,反应 NH2 + CH4NH3 + CH3 是主要的反应通道 .     

Unimolecular reactivity of strong metal-cation complexes in the gas phase: ethylenediamine-Cu(+)

The gas-phase reactions between ethylenediamine (en) and Cu(+) have been investigated by means of mass spectrometry techniques. The MIKE spectrum reveals that the adduct ions [Cu(+)(H(2)NCH(2)CH(2)NH(2))] spontaneously decompose by loosing H(2), NH(3) and HCu, the loss of hydrogen being clearly dominant. The spectra of the fully C-deuterated species show the loss of HD, NH(3) and CuD but no losses of H(2), D(2), NH(2)D, NHD(2), ND(3) or CuH are observed. This clearly excludes hydrogen exchange between the methylene and the amino groups as possible mechanisms for the loss of ammonia. Conversely, methylene hydrogen atoms are clearly involved in the loss of molecular hydrogen. The structures and bonding characteristics of the Cu(+)(en) complexes as well as the different stationary points of the corresponding potential energy surface (PES) have been theoretically studied by DFT calculations carried out at B3LYP/6-311+G(2df,2p)//B3LYP/6-311G(d,p) level. Based on the topology of this PES the most plausible mechanisms for the aforementioned unimolecular fragmentations are proposed. Our theoretical estimates indicate that Cu(+) strongly binds to en, by forming a chelated structure in which Cu(+) is bridging between both amino groups. The binding energy is quite high (84 kcal mol(-1)), but also the products of the unimolecular decomposition of Cu(+)(en) complexes are strongly bound Cu(+)-complexes.     

Vibrational spectra and analysis of acetohydrazide CH3-CO-NH-NH2

The structural stability of acetohydrazide CH(3)-CO-NH-NH(2) was investigated by DFT-B3LYP and ab initio MP2 calculations with 6-311+G** basis set. The C-N rotational barrier in the molecule was calculated to be about 26 kcal/mol that suggested the planar sp(2) nature of the nitrogen atom of the central NH moiety. The N atom of the terminal NH(2) group was predicted to highly prefer the pyramidal sp(3) structure with an inversion barrier of about 7-8 kcal/mol. The molecule was predicted to have a trans-syn (N-H bond is trans with respect to CO bond and NH(2) moiety is syn to C-N bond) conformation as the lowest energy structure. The vibrational frequencies were computed at B3LYP level of theory and normal coordinate calculations were carried out for the trans-syn acetohydrazide. Complete vibrational assignments were made on the basis of normal coordinate analyses and experimental infrared and Raman data.     

Exploring the dynamics of reaction N((2)D)+C2H4 with crossed molecular-beam experiments and quantum-chemical calculations

We conducted the title reaction using a crossed molecular-beam apparatus, quantum-chemical calculations, and RRKM calculations. Synchrotron radiation from an undulator served to ionize selectively reaction products by advantage of negligibly small dissociative ionization. We observed two products with gross formula C(2)H(3)N and C(2)H(2)N associated with loss of one and two hydrogen atoms, respectively. Measurements of kinetic-energy distributions, angular distributions, low-resolution photoionization spectra, and branching ratios of the two products were carried out. Furthermore, we evaluated total branching ratios of various exit channels using RRKM calculations based on the potential-energy surface of reaction N((2)D)+C(2)H(4) established with the method CCSD(T)/6-311+G(3df,2p)//B3LYP/6-311G(d,p)+ZPE[B3LYP/6-311G(d,p)]. The combination of experimental and computational results allows us to reveal the reaction dynamics. The N((2)D) atom adds to the C=C π-bond of ethene (C(2)H(4)) to form a cyclic complex c-CH(2)(N)CH(2) that directly ejects a hydrogen atom or rearranges to other intermediates followed by elimination of a hydrogen atom to produce C(2)H(3)N; c-CH(2)(N)CH+H is the dominant product channel. Subsequently, most C(2)H(3)N radicals, notably c-CH(2)(N)CH, further decompose to CH(2)CN+H. This work provides results and explanations different from the previous work of Balucani et al. [J. Phys. Chem. A, 2000, 104, 5655], indicating that selective photoionization with synchrotron radiation as an ionization source is a good choice in chemical dynamics research.     

CH2NH与O(3P)反应的量子化学及电子密度拓扑研究

采用B3LYP、MP2(full)和 QCISD 三种方法在6-311G(d, p)和aug-cc-pVDZ基组水平上对三线态O(3P)原子与CH2NH(s)的反应进行了详细的理论研究. 采用B3LYP和MP2(full)方法对反应势能面上的各驻点进行了几何构型优化, 通过振动频率分析证实了过渡态的真实性, 内禀反应坐标(IRC)跟踪验证了过渡态与反应物和产物的连接关系, 用上述三种方法计算得到了各反应通道的反应势垒. 对反应过程中的一些重要点进行了电子密度拓扑分析研究. 研究结果表明, O(3P)原子进攻CH2NH(s)中的N2原子和C1原子生成CH2NHO(t)和OCH2NH(t), CH2NHO(t)中N2上的H5可迁移到C1上异构化为CH3NO(t).     

Potassium cation affinities of matrix assisted laser desorption ionization matrices determined by threshold collision-induced dissociation: application to benzoic acid derivatives

Threshold collision-induced dissociation of K+(xBA) complexes with xenon is studied using guided ion beam mass spectrometry. The xBA ligands studied include benzoic acid and all of the mono- and dihydroxy-substituted benzoic acids: 2-, 3-, and 4-hydroxybenzoic acid and 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-dihydroxybenzoic acid. In all cases, the primary product corresponds to endothermic loss of the intact xBA ligand. The cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies (BDEs) for K+-xBA after accounting for the effects of multiple ion-neutral collisions, the kinetic and internal energy distributions of the reactants, and dissociation lifetimes. Density functional theory calculations at the B3LYP/6-31G* level of theory are used to determine the structures of the xBA ligands and their complexes with K+. Theoretical BDEs are determined from single-point energy calculations at the B3LYP/6-311+G(2d,2p) and MP2(full)/6-311+G(2d,2p) levels using B3LYP/6-31G* optimized geometries. Four favorable binding modes for the K+(xBA) complexes are found. In all complexes to an xBA ligand that does not have a 2-hydroxyl substituent, the most favorable binding mode corresponds to a single interaction with the carbonyl oxygen atom. Formation of a 4-membered ring via chelation interactions with both oxygen atoms of the carboxylic acid group is found to be the most favorable binding mode for all of the 2-hydroxy-substituted systems except K+(2,3-dihydroxybenzoic acid). In these complexes, a hydrogen-bonding interaction between the hydrogen atom of the carboxylic acid moiety and the oxygen atom of the 2-hydroxy substituent provides additional stabilization. Formation of a 5-membered chelation ring via interaction of K+ with the oxygen atoms of adjacent hydroxyl substituents is also favorable and corresponds to the ground-state geometry for the K+(23DHBA) complex. Formation of a 6-membered chelation ring via interaction of K+ with the carbonyl and 2-hydroxyl oxygen atoms is also quite favorable but does not correspond to the ground-state geometry for any of the systems examined here. The experimental BDEs determined here are in very good agreement with the calculated values.     

烯丙基自由基(·C3H5)与一氧化氮(NO)反应势能面的理论研究

在CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPE水平上对反应·CHCHCH3+NO进行了计算, 并建立了其单重态的反应势能面. 在该反应中, 分别找到生成P1(CH3CHO+HCN), P2(CH3CHO+HNC), P3(CH3CN+HCHO), P4(CH3CCH+HNO)的4条产物通道, 其中·CHCHCH3和NO中的氮原子直接连接形成m1(trans-CH3CHCHNO), m1经过顺反异构形成m2(cis-CH3CHCHNO), m2再经过CCNO四元环合, 然后发生环解离, 最后生成产物P1(CH3CHO+HCN)是最可行的产物通道, 其余三条通道为次要产物通道. 该体系中生成P1的反应路径与同类体系·C2H3+NO的主要反应路径相类似, 两者的差别是前者为动力学可行的反应, 而后者为动力学不可行反应, 这使得·CHCHCH3+NO反应比·C2H3+NO反应更具有实际意义.     

H+HCNO反应势能面的理论研究

在CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPVE水平下, 对反应H＋HCNO进行了研究. 建立了反应势能面, 揭示了该反应的反应机理, 通过H迁移、N—O键或C—N键断裂等多步反应, 得到4种产物, 其中最主要产物为P1(HCN+OH).     

Vibrational analyses of vinylsulfonamide CH2CHSO2NH2

The structure and conformational stability of vinylsulfonamide CH2CHSO2NH2 were investigated by DFT-B3LYP/6-311+G** and ab initio MP2/6-311+G** calculations. From the calculations the molecule was predicted to exist predominantly in the gauche-syn (vinyl group nearly eclipses one of the SO bonds and the NH2 and the SO2 moieties eclipse each other) conformation with the possibility of low abundance of the cis-syn and the gauche-anti forms. The asymmetric potential function for the internal rotation about CS bond was determined for the molecule. The vibrational frequencies were computed at DFT-B3LYP level for the gauche-syn conformer of the molecule and its d2(C2H3SO2ND2) and d3(C2D3SO2NH2) deuterated species. Normal coordinate calculations were then carried out and the potential energy distributions were calculated for the molecule.     

氟原子与反式1,3-丁二烯分子反应动力学的理论研究

Theoretical studies of F atom reaction with trans-1,3-butadiene were carried out at the CCSD(T)/6-311G(d,p)/B3LYP/6-311G(d,p) levels. Energies and structures for all reactants, products and transition states were determined. Two reaction pathways involving the formation of the complexes CH2CHCHFCH2 and CH2CHCHCH2F were found in this reaction. Theoretical results suggest that the H atom channel observed in previous crossed beam experiment occurs likely via these two long-lived complex formation pathways. For the complex CH2CHCHFCH2 pathway, another reaction channel (C2H3+C2H3F) is also accessible. Relative importance of the C2H3+C2H3F channel versus the H formation channel via the same reaction pathway has also been estimated, suggesting that it would be difficult to observe the C2H3+C2H3F channel in a crossed molecular beam experiment. Theoretical analysis also shows that the HF formation proceeds via direct abstraction mechanisms, though it is likely a minor process in this reaction.     

Theoretical Investigation of CH3CF2O2+HOO Reaction

The reactions of CH3CF2O2 with HOO are important chemical cyclic processes of photochemical contamination. In this paper, the reaction pathways and reaction mechanism of CH3CF2O2+HOO are investigated extensively with the Gaussian 98 package at the B3LYP/6-311++G** basis sets. The use of vibrational mode analysis and electron population analysis to reveal the reaction mechanism is firstly reported. The study shows that CH3CF2CO2+HOO→IM1→TS1→CH3CF2O2H+O2 channel is the energetically most favorable, CH3CF2CO2H and O2 are the principal products, and the formation of CH3OH and CF2O is also possible.     

Theoretical Study of Reaction Mechanism of 1-Propenyl Radical with NO

The reaction system of 1-propenyl radical with NO is an ideal model for studying the intermolecular and intramolecular reactions of complex organic free radicals containing C=C double bonds. On the basis of the full optimization of all species with the Gaussian 98 package at the B3LYP/6-311++G** level, the reaction mechanism was elucidated extensively using the vibrational mode analysis. There are seven reaction pathways and five sets of small molecule end products: CH2O+CH3CN, CH2CHCN+H2O, CH3CHO+HCN, CH3CHO+HNC, and CH3CCH+HNO. The channel of C3H5￠+NO→ IM1→TS1→IM2→TS2→IM3→TS3→CH3CHO+HCN is thermodynamically most favorable.     

烯丙基自由基(·C3H5)与氧气(O2)反应机理的理论计算

用量子化学计算方法对CH3CH=·CH与O2气的反应机理进行了理论研究, 在B3LYP/6-311G(d,p) 水平下优化稳定分子结构和寻找过渡态, 并在此构型的基础上, 采用CCSD(T)/6-311G(d,p)方法得到各驻点的高级单点能量. 找到主要路径R(CH3CH=·CH+O2)→m1(trans-CH3CH=CHOO)→m2(形成COO三元环)→m3(C—C键断裂,同时生成CH3CH—O—CHO)→P2(C—O键断裂生成CH3CHO+CHO); 并与C2H3等共轭体系进行了对比.     

A theoretical study of hydration effects on the prototropic tautomerism of selenouracils

The prototropic tautomerism of 2-, 4-selenouracil and 2,4-diselenouracil has been studied using density functional theory (DFT) methods, at the B3LYP/6-311 + G(3df,2p)//B3LYP/6-31G(d,p) level. The relative stability order of selenouracil tautomers does not resemble that of uracil tautomers, but it is similar to that of thiouracils, even though the energy gaps between the different tautomers of selenouracils are smaller than for thiouracils. The tautomerism activation barriers are high enough as to conclude that only the oxo-selenone or the diselenone structures should be found in the gas phase. The specific interaction with one water molecule reduces these barriers by a half, but still the oxo-selenone form is always the most stable tautomer. The addition of a second water molecule has a relatively small effect, as well as bulk effects, evaluated by means of a continuum-polarized model. For isolated 2- and 4-selenouracils, the more favorable tautomerization process corresponds to a hydrogen transfer towards the selenium atom, the activation barriers for transfer towards the oxygen atom being much higher. This situation changes when specific and bulk effects are included, and the latter process becomes the more favorable one. For 2,4-diselenouracil the more favorable tautomerization, in the gas phase, corresponds to the H shift from N1 to the Se atom at C2, while solvation effects favor the transfer from N3 to the Se atom at C4.     

H-Atom abstraction from CH(3)NHNH(2) by NO(2): CCSD(T)/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) and CCSD(T)/6-311+G(2df,p)//CCSD/6-31+G(d,p) calculations

Stationary points of paths for H atom abstraction from CH(3)NHNH(2) (monomethylhydrazine) by NO(2) were characterized via CCSD(T)/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) and CCSD(T)/6-311+G(2df,p)//CCSD/6-31+G(d,p) calculations. Five transition states connecting CH(3)NHNH(2)-NO(2) complexes to a manifold that includes CH(3)NHNH-HONO, CH(3)NNH(2)-HONO, CH(3)NNH(2)-HNO(2), and CH(3)NHNH-HNO(2) complexes were identified. Transition states that connect CH(3)NHNH-HONO, CH(3)NNH(2)-HONO, CH(3)NNH(2)-HNO(2), and CH(3)NHNH-HNO(2) complexes to each other via H atom exchange and/or hindered internal rotation were also identified. The high point in the minimum energy path from the CH(3)NHNH(2) + NO(2) reactant asymptote to the manifold of HONO-containing product states is a transition state 8.6 kcal/mol above the reactant asymptote. From a kinetics standpoint, this value is considerably higher than the 5.9 kcal/mol value that was estimated for it based on theoretical results for H atom abstraction from NH(3) by NO(2).     

CH3 CH2 +N(4S)反应机理的理论研究

The reaction for CH3CH2+N(4S) was studied by ab initio method. The geometries of the reactants, intermediates, transition states and products were optimized at MP2/6-311+G(d,p) level. The corresponding vibration frequencies were calculated at the same level. The single point calculations for all the stationary points were carried out at the QCISD(T)/ 6-311+G(d,p) level using the MP2/6-311+G(d,p) optimized geometries. The results of the theoretical study indicate that the major products are the CH2CH2+3NH and H2CN＋CH3, and the minor products are the CH3CHN+H in the reaction. The majority of the products CH2CH2+3NH are formed via a direct hydrogen abstraction channel. The products H2CN＋CH3 are produced via an addition/dissociation channel. The products CH3CHN+H are produced via an addition/dissociation channel.     

Isomerization and fragmentation reactions of gaseous dimethyl phenylarsane radical cations and methyl phenylarsenium cations. A study by tandem mass spectrometry and density functional theory calculations

The unimolecular reactions of the radical cation of dimethyl phenylarsane, C6H5As(CH3)2, 1*+ and of the methyl phenylarsenium cation, C6H5As+CH3, 2+, in the gas phase were investigated using deuterium labeling and methods of tandem mass spectrometry. Additionally, the rearrangement and fragmentation processes were analyzed by density functional theory (DFT) calculations at the level UBHLYP/6- 311+G(2d,p)//UBHLYP/5-31+G(d). The molecular ion 1*+ decomposes by loss of a .CH3 radical from the As atom without any rearrangement, in contrast to the behavior of the phenylarsane radical cation. In particular, no positional exchange of the H atoms of the CH3 group and at the phenyl ring is observed. The results of DFT calculations show that a rearrangement of 1*+ by reductive elimination of As and shift of the CH3 group is indeed obstructed by a large activation barrier. The MIKE spectrum of 2+ shows that this arsenium cation fragments by losses of H2 and AsH. The fragmentation of the trideuteromethyl derivative 2-d3+ proves that all H atoms of the neutral fragments originate specifically from the methyl ligand. Identical fragmentation behavior is observed for metastable m-tolyl arsenium cation, m-CH3C6H4As+H, 2tol+. The loss of AsH generates ions C7H7+ which requires rearrangement in 2+ and bond formation between the phenyl and methyl ligands prior to fragmentation. The DFT calculations confirm that the precursor of this fragmentation is the benzyl methylarsenium cation 2bzl+, and that 2bzl+ is also the precursor ion fo the elimination of H2. The analysis of the pathways for rearrangements of 2+ to the key intermediate 2bzl+ by DFT calculations show that the preferred route corresponds to a 1,2-H shift of a H atom from the CH3 ligand to the As atom and a shift of the phenyl group in the reverse direction. The expected rearrangement by a reductive elimination of the As atom, which is observed for the phenylarsenium cation and for halogeno phenyl arsenium cations, requires much more activation enthalpy.     

类硅烯H2C＝SiLiBr与RH (R＝F, OH, NH2)的插入反应

采用DFT B3LYP和QCISD方法研究了类硅烯H2C＝SiLiBr与RH (R＝F, OH, NH2)的插入反应. 在B3LYP/6- 311＋G(d,p)水平上优化了反应势能面上的驻点构型. 结果表明, H2C＝SiLiBr与HF, H2O或NH3发生插入反应的机理相同. QCISD/6-311＋＋G(d,p)//B3LYP/6-311＋G(d,p)计算的三个反应的势垒分别为148.62, 164.42和165.07 kJ•mol－1, 反应热分别为－69.63, －43.02和－28.27 kJ•mol－1. 相同条件下发生插入反应时, 反应活性都是H—F＞H—OH＞H—NH2.     

硫原子上亲核取代反应的密度泛函理论研究

在B3LYP/6-311 G(2df,p)的水平上,对反应X- CH3SCl(X=F,Cl,Br,I)进行了理论研究.计算结果表明:X-(X=Cl,Br,I)与CH3SCl作用时,实际发生的是在硫原子上而不是在碳原子上的亲核取代反应,而且属于加成-消去机理.但是F-与CH3SCl作用则容易发生脱质子反应.     

C6H5—H…X分子间氢键的理论计算

利用密度泛函理论B3LYP方法, 在6-311+G(3df,2p)水平上对C6H5—H…X型分子间氢键进行了几何构型优化、氢键相互作用能、电子密度分布等计算. 其中C6H6为质子供体, HCOH、H2O、NH3、CH2NH和HCN为质子受体. 从电荷布居分析、自然键轨道等角度详细地讨论了C6H5—H…X 体系中, 共轭π键、O和N的不同键型结构对氢键形成的影响以及孤电子对与C—H 反键轨道之间的相互作用(n→σ*)等.