Theoretical study of mechanism of cycloaddition reaction between dimethyl‐silylene carbene [(CH3)2SiC:] and formaldehyde

The mechanism of the cycloaddition reaction between singlet dimethyl‐silylene carbene and formaldehyde has been investigated with MP2/6‐31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by zero‐point energy and CCSD (T)//MP2/6‐31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The main products of first dominant reaction pathway are a planar four‐membered ring product (P4) and its H‐transfer product (P4.2). The main product of second dominant reaction pathway is a silicic bis‐heterocyclic compound (P5). © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical study of mechanism of cycloaddition reaction between dimethylmethylenesilylene and formaldehyde

The mechanism of cycloaddition reaction between singlet dimethylmethylenesilylene and formaldehyde has been investigated with MP2/6‐31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of different conformations are calculated by CCSD(T)//MP2/6‐31G* method. From the potential energy surface, it can be considered in thermodynamics and dynamics that reaction (1) and reaction (4) are the two dominant competitive reaction channels of cycloaddition reaction between dimethylmethylenesilylene and formaldehyde. The reaction process of reaction (1) is that: the two reactants (R1, R2) first form intermediates INT1a and INT1b through two reaction paths, a and b, which are barrier‐free exothermic reactions of 31.8 and 43.9 kJ/mol; then, INT1a and INT1b isomerize to a four‐membered ring product P1 via transition states TS1a and TS1b, with energy barriers of 26.3 and 24.4 kJ/mol. Reaction (4) also has two reaction paths, a and b, each of which consists of three steps are as follows: (i) the two reactants (R1, R2) first form intermediates INT3a and INT3b, which are barrier‐free exothermic reactions of 64.5 and 44.2 kJ/mol. (ii) INT3a and INT3b further react with formaldehyde (R2) to form intermediates INT4a and INT4b, through barrier‐free exothermic reactions of 22.9 and 22.2 kJ/mol. (iii) INT4a and INT4b then isomerize to form silapolycyclic product P4 via transition states TS4a and TS4b, with energy barriers of 39.7 and 29.3 kJ/mol. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Theoretical study of mechanism of cycloaddition reaction between dimethylmethylene carbene and formaldehyde

The cycloaddition mechanism of forming a polycyclic compound between singlet dimethylmethylene carbene(R1) and formaldehyde(R2) has been investigated with MP2/6‐31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated with CCSD(T)//MP2/6‐31G* method. From the potential energy profile, it can be predicted that the dominant reaction pathway of the cycloadditional reaction between singlet dimethylmethylene carbene and formaldehyde consists of two steps: (1) the two reactants(R1, R2) firstly form an energy‐enricheded intermediate (INT1a) through a barrier‐free exothermic reaction of ΔE = 11.3 kJ/mol. (2) Intermediate (INT1a) then isomerizes to a three‐membered product (P1) via a transition state (TS1a) with an energy barrier of 20.0 kJ/mol. The dominant reaction has an excellent selectivity and differs considerably from its competitive reactions in reaction rate. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Theoretical study of mechanism of cycloaddition reaction between singlet dichlorosilylene carbene (Cl<Subscript>2</Subscript>Si=C:) and formaldehyde

The mechanism of the cycloaddition reaction between singlet dichlorosilylene carbene (Cl₂Si=C:) and formaldehyde has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by Zero-point energy and CCSD (T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The first dominant reaction pathway consists of two steps: (1) the two reactants (R1, R2) firstly form a four-membered ring intermediate (INT4) through a barrier-free exothermic reaction of 387.9 kJ/mol; (2) intermediate (INT4) then isomerizes to H-transfer product (P4.2) via a transition state (TS4.2) with energy barrier of 4.7 kJ/mol. The second dominant reaction pathway as follows: on the basis of intermediate (INT4) created between R1 and R2, intermediate (INT4) further reacts with formaldehyde (R2) to form the intermediate (INT5) through a barrier-free exothermic reaction of 158.3 kJ/mol. Then, intermediate (INT5) isomerizes to a silicic bis-heterocyclic product (P5) via a transition state (TS5), for which the barrier is 40.1 kJ/mol.     

Theoretical study on the mechanism of cycloaddition reaction between dimethyl germylidene and formaldehyde

The cycloaddition mechanism of the reaction between singlet dimethyl germylidene and formaldehyde has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated with CCSD (T)//MP2/6-31G* method. From the potential energy profile, we predict that the cycloaddition reaction between singlet dimethyl germylidene and formaldehyde has two dominant reaction pathways. First dominant reaction pathway consists of three steps: (1) the two reactants (R1, R2) firstly form an intermediate INT1a through a barrier-free exothermic reaction of 43.0 kJ/mol; (2) INT1a then isomerizes to a four-membered ring compound P1 via a transition state TS1a with an energy barrier of 24.5 kJ/mol; (3) P1 further reacts with formaldehyde(R2) to form a germanic heterocyclic compound INT3, which is also a barrier-free exothermic reaction of 52.7 kJ/mol; Second dominant reaction pathway is as following: (1) the two reactants (R1, R2) firstly form a planar four-membered ring intermediate INT1b through a barrier-free exothermic reaction of 50.8 kJ/mol; (2) INT1b then isomerizes to a twist four-membered ring intermediate INT1.1b via a transition state TS1b with an energy barrier of 4.3 kJ/mol; (3) INT1.1b further reacts with formaldehyde(R2) to form an intermediate INT4, which is also a barrier-free exothermic reaction of 46.9 kJ/mol; (4) INT4 isomerizes to a germanic bis-heterocyclic product P4 via a transition state TS4 with an energy barrier of 54.1 kJ/mol.     

Theoretical studies of mechanism of cycloaddition reaction between germylidene and formaldehyde

Mechanism of the cycloadditional reaction between singlet germylidene (R1) and formaldehyde (R2) has been investigated with MP2/6‐31G* method, including geometry optimization, and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by CCSD(T)//MP2/6‐31G* method. From the potential energy profile, it can be predicted that the dominant reaction pathway of the cycloadditional reaction between singlet germylidene and formaldehyde is reaction (4) , which consists of three steps: the two reactants (R1, R2) first form an intermediate INT1b through a barrier‐free exothermic reaction of 28.1 kJ/mol; this intermediate reacts further with formaldehyde (R2) to give an intermediate INT4, which is also a barrier‐free exothermic reaction of 37.2 kJ/mol; subsequently, the intermediate INT4 isomerizes to a heteropolycyclic germanic compound P4 via a transition state TS4, for which the barrier is 18.6 kJ/mol. The dominant reaction has an excellent selectivity and differs considerably from its competitive reactions in thermodynamic property and reaction rate. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Theoretical investigation on mechanism for OH-initiated oxidation of CH2=C(CH3)CH2OH

The mechanism of the gas-phase reaction OH with CH₂=C(CH₃)CH₂OH (2-methyl-2-propen-1-ol) has been elucidated using high-level ab initio method, i.e., CCSD(T)/6-311++g(d,p)//MP2(full)/6-311++g(d,p). Various possible H-abstraction and addition–elimination pathways are identified. The calculations indicate that the addition–elimination mechanism dominates the OH+MPO221 reaction. The addition reactions between OH radicals and CH₂=C(CH₃)CH₂OH begin with the barrierless formation of a pre-reactive complex in the entrance channel, and subsequently the CH₂(OH)C(CH₃)CH₂OH (IM1) and the CH₂C(OH)(CH₃)CH₂OH (IM2) are formed by OH radicals’ electrophilic additions to the double bond. IM1 can easily rearrange to IM2 via a 1,2-OH migration. Subsequently, rearrangement of IM2 to form (CH₃)₂C(OH)CH₂O (IM11) followed by dissociation to HCHO + (CH₃)₂COH (P21) is the most favorable pathway. The decomposition of IM2 to CH₂OH + CH₂=C(OH)CH₃ (P16) is the secondary pathway. The other pathways are not expected to play any important role in forming final products.     

Theoretical study on the mechanism of the cycloaddition reaction between stannylene and ethylene or formaldehyde

The mechanism of the cycloaddition reaction of singlet stannylene and ethylene or formaldehyde has been studied by using density functional theory. The geometrical parameters, harmonic vibrational frequencies and energies of stationary points for potential energy surface are calculated by RB3LYP/3–21G* method. The results show that the two reaction processes are both two steps: (1) stannylene and ethylene or formaldehyde form an energy‐rich intermediate complex respectively, which is an exothermal reaction with no barrier; (2) two intermediate complexes isomerize to the product, respectively, with the barriers of these two reactions being 52.97 and 45.15 kJ/mol at RB3LYP/3–21G* level.     

Theoretical study on the mechanism of cycloaddition reaction between dichlorogermylene silylene (Cl<Subscript>2</Subscript>Ge=Si:) and acetaldehyde

The mechanism of the cycloaddition reaction between singlet state dichlorogermylene silylene (Cl₂Ge=Si:) and acetaldehyde has been investigated with the MP2/cc-pvtz//MP2/6-31G* method. According to the potential energy profile, it can be predicted that the reaction has four competitive dominant reaction pathways. The presented rule of this reaction is that the 3p unoccupied orbital of Si: atom in dimethylgermylene silylene(Cl₂Ge=Si:) inserts the π orbital of acetaldehyde from the oxygen side, resulting in the formation of intermediate. In the intermediate and two reactants, two four-membered ring silylenes, with Si and O in the syn-position and opposite orientation, respectively, are generated, as the [2+2] cycloaddition reaction has occurred between the two bonding π orbital in dichlorogermylene silylene and acetaldehyde. Because of the unsaturated property of Si: atom in the two four-membered ring silylenes, they can further react with acetaldehyde to form two silicic bis-heterocyclic compounds. Simultaneity, the drive of ringlet tensility and unsaturated property of Si: atom in the four-membered ring silylene makes it isomerize into a distorted four-membered ring product and a Cl-transfer product and a H-transfer product, respectively.     

Theoretical study for the CH3C(O)(CH2)2OH + OH reaction

The mechanisms and the kinetics of the OH radical reaction with 4-hydroxy-2-butanone (4H2B) are investigated theoretically. Five hydrogen-abstraction channels are identified for the title reaction. The first potential energy profile of the title reaction is presented. The rate constants for each reaction channel are evaluated using transition state theory method in the temperature range of 200–1,000 K. Branching ratio of the title reaction is calculated and plotted. It is shown that the “in-plane hydrogen abstraction” from the methoxy end is the dominant channel, and the other hydrogen-abstraction channels play the minor role. The comparison between theoretical and experimental results is discussed. The three-parameter Arrhenius expression for the rate constants is also provided.     

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.     

硅烯与甲醛环加成反应的理论研究

本文用RHF/6-31G^*解析梯度方法研究了单重态硅烯与甲醛环加成反应的机理,用二级微扰方法对各构型的能量进行了相关能校正,并用统计热力学方法和过渡态理论计算了该反应在不同温度下的热力学函数的变化和动力学性质。结果表明,此反应历程由两步组成:1)硅烯与甲醛生成一中间配合物,是一无势垒的放热反应,2)中间配合物异构化为产物,此步势垒经零点能校正后只有51.4kJ·mol^-^1(MP2/6-31G^*//6-31G^*);从热力学和动力学的综合角度考虑,该反应在300～400K温度下进行为宜,如此,反应既有较大的自发趋势和平衡常数,又具有较快的反应速率。     

Direct detection of polyynes formation from the reaction of ethynyl radical (C2H) with propyne (CH3-C[triple bond]CH) and allene (CH2=C=CH2)

The reactions of the ethynyl radical (C(2)H) with propyne and allene are studied at room temperature using an apparatus that combines the tunability of the vacuum ultraviolet radiation of the Advanced Light Source at Lawrence Berkeley National Laboratory with time-resolved mass spectrometry. The C(2)H radical is prepared by 193-nm photolysis of CF(3)CCH and the mass spectrum of the reacting mixture is monitored in time using synchrotron-photoionization with a dual-sector mass spectrometer. Analysis using photoionization efficiency curves allows the isomer-specific detection of individual polyynes of chemical formula C(5)H(4) produced by both reactions. The product branching ratios are estimated for each isomer. The reaction of propyne with ethynyl gives 50-70% diacetylene (H-C[triple bond]C-C[triple bond]C-H) and 50-30% C(5)H(4), with a C(5)H(4)-isomer distribution of 15-20% ethynylallene (CH(2)=C=CH-C[triple bond]CH) and 85-80% methyldiacetylene (CH(3)-C[triple bond]C-C[triple bond]CH). The reaction of allene with ethynyl gives 35-45% ethynylallene, 20-25% methyldiacetylene and 45-30% 1,4-pentadiyne (HC[triple bond]C-CH(2)-C[triple bond]CH). Diacetylene is most likely not produced by this reaction; an upper limit of 30% on the branching fraction to diacetylene can be derived from the present experiment. The mechanisms of polyynes formation by these reactions as well as the implications for Titan's atmospheric chemistry are discussed.     

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,…     

Ab initio study of mechanism of forming bis-heterocyclic compound with Si and Ge between silylene germylene (H2Si=Ge:) and formaldehyde

The mechanism of the cycloaddition reaction between singlet state silylene germylene (H₂Si=Ge:) and formaldehyde has been investigated with the CCSD(T)//MP2/cc-pvtz method, from the potential energy profile, it could be predicted that the reaction has one dominant reaction pathway. The reaction rules presented is that [2?+?2] cycloaddition reaction between two reactants firstly generates a Si-heterocyclic four-membered ring germylene. Because of the 4p unoccupied orbital of the Ge atom in (the) Si-heterocyclic four-membered ring germylene and the ?? orbital of formaldehyde forming a ??????p donor?Cacceptor bond, the Si-heterocyclic four-membered ring germylene further combines with formaldehyde to form an intermediate. Because the Ge atom in intermediate happens sp ³ hybridization after transition state, then, intermediate isomerizes to a bis-heterocyclic compound with Si and Ge via a transition state.     

Xenon Trioxide Adducts of O-Donor Ligands; [(CH3)2CO]3XeO3, [(CH3)2SO]3(XeO3)2, (C5H5NO)3(XeO3)2, and [(C6H5)3PO]2XeO3

Xenon trioxide (XeO₃) forms adducts with triphenylphosphine oxide, dimethylsulfoxide, pyridine-N-oxide, and acetone by coordination of the ligand oxygen atoms to the Xe^VI atom of XeO₃. The crystalline adducts were characterized by low-temperature, single-crystal X-ray diffraction, and Raman spectroscopy. Unlike solid XeO₃, which detonates when mechanically or thermally shocked, solid (C₅H₅NO)₃(XeO₃)₂, [(C₆H₅)₃PO]₂XeO₃, and [(CH₃)₂SO]₃(XeO₃)₂ are insensitive to mechanical shock. The [(CH₃)₂SO]₃(XeO₃)₂ adduct slowly decomposes over several days to (CH₃)₂SO₂, Xe, and O₂. All three complexes undergo rapid deflagration when ignited by a flame. Both [(C₆H₅)₃PO]₂XeO₃ and (C₅H₅NO)₃(XeO₃)₂ are room-temperature stable and the [(CH₃)₂CO]₃XeO₃ complex dissociates at room temperature to form a stable solution of XeO₃ in acetone. The xenon coordination sphere of [(C₆H₅)₃PO]₂XeO₃, a distorted square-pyramid, provides the first example of a five-coordinate XeO₃ complex with only two Xe- - -O adduct bonds. The xenon coordination spheres of the remaining adducts are distorted octahedra, comprised of three Xe- - -O secondary bonds that are approximately trans to the primary Xe−O bonds of XeO₃. Quantum-chemical calculations were used to assess the nature of the Xe- - -O adduct bonds, which are described as predominantly electrostatic bonds between the nucleophilic oxygen atoms of the bases and the σ-holes of the electrophilic xenon atoms.     

Theoretical study of mechanism of cycloaddition reaction between dichloro‐germylene carbene (Cl2GeC:) and aldehyde

The mechanism of the cycloaddition reaction between singlet dichloro‐germylene carbene and aldehyde has been investigated with MP2/6‐31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by zero‐point energy and CCSD (T)//MP2/6‐31G* method. From the potential energy profile, it can be predicted that the reaction has two competitive dominant reaction pathways. The channel (A) consists of four steps: (1) the two reactants (R1, R2) first form an intermediate INT2 through a barrier‐free exothermic reaction of 142.4 kJ/mol; (2) INT2 then isomerizes to a four‐membered ring compound P2 via a transition state TS2 with energy barrier of 8.4 kJ/mol; (3) P2 further reacts with aldehyde (R2) to form an intermediate INT3, which is also a barrier‐free exothermic reaction of 9.2 kJ/mol; (4) INT3 isomerizes to a germanic bis‐heterocyclic product P3 via a transition state TS3 with energy barrier of 4.5 kJ/mol. The process of channel (B) is as follows: (1) the two reactants (R1, R2) first form an intermediate INT4 through a barrier‐free exothermic reaction of 251.5 kJ/mol; (2) INT4 further reacts with aldehyde (R2) to form an intermediate INT5, which is also a barrier‐free exothermic reaction of 173.5 kJ/mol; (3) INT5 then isomerizes to a germanic bis‐heterocyclic product P5 via a transition state TS5 with an energy barrier of 69.4 kJ/mol. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Schwermetall-π-Komplexe. IX. Die Kettenpolymere [(1,2- (CH3)2C6H4BiCl3)2], [(1,3) (CH3)2C6H4BiCl3)2] und [(1,4- (CH3)2C6H4BiCl3)2]

Heavy Metal π-Complexes. IX. The Chain Polymers [(1,2- (CH₃)₂C₆H₄BiCl₃)₂], [(1,3- (CH₃)₂C₆H₄BiCl₃)₂] and [(1,4- (CH₃)₂C₆H₄BiCl₃)₂] In the crystal structures of the three solid state complexes (C₆H₄(CH₃)₂BiCl₃ (C₆H₄(CH₃)₂ = o-xylene: 1 , m-xylene: 2 , p-xylene: 3 ) quasi-dimeric units of almost undistorted, arene coordinated BiCl₃ fragments can be found that are further associated via additional Bi? Cl contacts to form one-dimensional polymeric chains. Whereas the chains of 2 and 3 are constituted by Bi₂Cl₂ four-membered rings only, further Cl-bridging in 1 leads to additional trigonal-bipyramidal arrangements with Bi atoms exhibiting coordination numbers of 3 + 3 + 1 and 3 + 2 + 1, respectively (prim. + sec. Cl contacts + arene). The arene-metal bonding is characterized by Bi-arene distances in the range from 297 – 306 pm, including ring slippages of 24 –41 pm and 73 pm with the Bi atoms being six and seven coordinated, respectively. The direction of this slipping with respect to the arene's methylation sites cannot be understood in terms of electronic influences but is shown to be caused by steric demands. The values IP₁ of the arenes prove to determine the colours of the complexes.     

Gold-Stickstoff-Heterocyclen. Synthese,Eigenschaften und Struktur von [(CH3)2AuNH2]4 und [(CH3)2AuN(CH3)2]2

Gold Nitrogen Heterocycles. Synthesis, Properties, and Structure of [(CH₃)₂AuNH₂]₄ and [(CH₃)₂AuN(CH₃)₂]₂ Dimethyl gold iodide reacts with alkali metal amides to form Au-N heterocycles. KNH₂ yields the eight-membered ring [(CH₃)₂AuNH₂]₄, whereas with LiN(CH₃)₂ the four-membered ring [(CH₃)₂AuN(CH₃)₂]₂ is obtained. The light sensitive, cyclic gold amides are stable against hydrolysis and do not react with Lewis bases. [(CH₃)₂AuN(CH₃)₂]₂ crystallizes monoclinic in the space group P2₁/c with Z = 2. The molecules exhibit the symmetry D_2h. Symmetrical amido bridges form a planar Au-N heterocyclus with distances Au-N = 214 pm.