Theoretical study on the radical–radical reaction mechanism of CH2I + NO2

The mechanisms of CH₂I with NO₂ reaction were investigated on the singlet and triplet potential energy surfaces (PESs) by the UB3LYP method. The energetic information is further refined at the UCCSD(T) and UQCISD(T) levels of theory. Our results indicated that the title reaction is more favorable on the singlet PES thermodynamically, and less competitive on the triplet one. On the singlet PES, the title reaction is most likely to be initiated by the carbon-to-oxygen approach forming the adduct IM1 (H₂ICONO-trans) without any transition state, which can isomerizes to IM2 (H₂ICNO₂) and IM3 (H₂ICONO-cis), respectively. The most feasible pathway is the 1, 3-I shift with C–I and O–N bonds cleavage along with the N–I bond formation of IM1 lead to the product P1 (CH₂O + INO), which can further dissociate to give P3 (CH₂O + I + NO). The competitive pathway is 1, 3-H shift associated with O–N bond rupture of IM1 to form P2 (CHIO + HNO). The theoretically obtained major product CH₂O and adducts IM1 and IM2 are in good agreement with the kinetic detection in experiment. The similarities and discrepancies between CH₂I + NO₂ and CH₂Br + NO₂ reactions are discussed in terms of the electronegativity of halogen atom and the barrier height of the rate-determining process. The present study may be helpful for further experimental investigation of the title reaction.     

Theoretical study on the reaction mechanism of CH2SH + NO2

The mechanisms of CH₂SH with NO₂ reaction were investigated on the singlet and triplet potential energy surfaces (PES) at the BMC-CCSD//B3LYP/6-311 + G(d,p) level. The result shows that the title reaction is more favourable on the singlet PES thermodynamically, and it is less competitive on the triplet PES. On the singlet PES, the initial addition of CH₂SH with NO₂ leads to HSCH₂NO₂ (IM2) without any transition state, followed by a concerted step involving C–N fission and shift of H atom from S to O giving out CH₂S + trans-HONO, which is the major products of the title reaction. With higher barrier height, the minor products are CH₂S + HNO₂, formed by a similar concerted step from the initial adduct HSCH₂ONO (IM1). The direct abstraction route of H atom in SH group abstracted by O atom might be of some importance. It starts from the addition of the reactants to form a weak interaction molecular complex (MC3), subsequently, surmounts a low barrier height leading to another complex (MC2), which gives out CH₂S + trans-HONO finally. Other direct hydrogen abstraction channels could be negligible with higher barrier heights and less stable products.     

Theoretical study on the gas phase reaction of acrylonitrile with atomic hydrogen

The complex potential energy surface of the H + CH₂=CHCN reaction has been investigated at the BMC-CCSD level based on the geometric parameters optimized at the BHandHLYP/6-311++G(d,p) level. This reaction is revealed to be one of the significant loss processes of acrylonitrile. The BHandHLYP and M05-2X methods are employed to obtain initial geometries. The reaction mechanism confirms that H can attack on the C=C double bond or C and N atom of –CN group to form the chemically activated adducts IM1 (CH₃CHCN), IM2 (CH₂CH₂CN), IM3′ (CH₂=CHCHN) and IM5 (CH₂=CHCNH), and direct H-abstraction paths may also occur. Temperature- and pressure-dependent rate constants have been carried out using Rice–Ramsperger–Kassel–Marcus theory with tunneling correction. IM1 (CH₃CHCN) formed by collisional stabilization is the major product at the 760 Torr pressure of H₂ and in the temperature range (200–1,600 K); whereas the production of IM2 (CH₂CH₂CN) is the main channel at 1,600–3,000 K. The calculated rate constants are in good agreement with the experimental data.     

Ab initio studies of isomerization and dissociation reactions of methyl peroxynitrate

Using the CCSD(T)/cc-pVDZ//B3LYP/6-311G(2d,2p) method, we calculated the detailed potential energy surfaces (PESs) for the unimolecular isomerization and decomposition of methyl peroxynitrate (CH₃O₂NO₂). The results show that there are the two most stable isomers, IS1a and IS1b, which are a pair of mirror image isomers. From IS1a and IS1b, different isomerization and unimolecular decomposition reaction channels have been studied and discussed. Among them, the predominant thermal decomposition pathways are those leading to CH₃O₂ + NO₂ and cis-CH₃ONO + O₂. The former is the lowest-energy path through the direct O–N bond rupture in IS1a or IS1b. The PES along the O–N bond in IS1a has been scanned, where the energy of IS1a reaches maximum value of 23.5 kcal/mol when the O–N bond is stretched to about 2.8 Å. This energy is 2.7 kcal/mol larger than the O–N bond dissociation energy (BDE) and 2.8 kcal/mol larger than the experimental active energy. In addition, because the energy barriers of IS1a isomerization to IS2a are 23.8 kcal/mol, close to the 20.8 kcal/mol O–N BDE in IS1a or IS1b, the isomerization reaction may compete with the direct bond rupture dissociation reaction.     

Insight into detailed mechanism of the atmospheric reaction of imidogen with hydroxyl: a computational study

The details of reaction mechanism of imidogen (NH) and hydroxyl radicals are explored at the UMP2(FC)/cc–pVDZ and PMP4(FC,SDTQ)/cc–pVQZ//UMP2 + ZPE levels, theoretically. The initial association between NH and OH radicals leads to the formation of the intermediates, NH…OH, HN…HO, cis HNOH, and trans HNOH, through the barrierless and exothermic processes. By starting from the initial intermediates, all possible paths for the formation of H + HNO, H₂ + NO, H₂O + ⁴N, H₂N + ³O, and H + ³HON products are investigated on potential energy surface. The results reveal that H₂O + ⁴N is the main product involved in the mechanism of hydrogen atom abstraction of NH by OH radical through the intermediate NH…OH.     

Computational study on the mechanisms and kinetics of the CH<Subscript>2</Subscript>=CHCH<Subscript>2</Subscript>I with OH reaction

The potential energy surface for the reaction of OH with CH₂═CHCH₂I has been studied at the CCSD(T)//M06-2X/6-311++G(d,p) level of theory. Three different reaction entrances were revealed, namely, terminal-C addition, central-C addition, and H-abstraction, leading to CH₂OHCHCH₂I (IM1), CH₂CHOHCH₂I (IM2), and H₂O?+?C₃H₄I, respectively. Several conceivable decomposition and isomerization channels were also examined for IM1 and IM2. The total and individual rate constants were calculated by using multichannel RRKM and TST theories over a wide range of temperatures (200–3000 K) and pressures(10^?14–10¹⁴ Torr).     

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 reaction mechanisms of CH2SH + NO reaction

The mechanisms for the CH₂SH + NO reaction were investigated on both of the singlet and triplet PES at the BMC-CCSD//B3LYP/6-311+G(d,p) level. The results indicate that the singlet PES is much lower than the triplet PES energetically; therefore, the reaction occurs on the singlet PES dominantly. The most favorable channel on the singlet PES takes place by a barrierless addition of N atom to CH₂SH radical to form HSCH₂NO. Subsequently, the rearrangement of the initial adduct HSCH₂NO (IM1) to form another intermediate IM3 via a four-center transition state, followed by the C–O bond fission in IM3 leading to the major product CH₂S + HNO. Due to high barriers, other product including HC(N)SH + HO, HON + CH₂S, and HNO + CHSH could be negligible. The direct abstraction channel was also determined to yield CH₂S + HON. With high barrier (33.3 kcal/mol), it is not competitive with the addition channel, in which all stationary points are lower than reactant energetically. While on the triplet PES, with the lowest barrier height (18.8 kcal/mol), the direct N-abstracted channel to form CH₂S + HNO is dominant. However, it is not competitive with the channels on the singlet PES. Our results are in good accordance with experimental conclusions that the reaction proceeds via addition mechanism.     

Ab initio and DFT Study of the Structural Properties and Thermochemistry of CH3S(O)2OONO2 Atmospheric Molecule and CH3S(O)2OO· Radical

The conformational properties of methanesulfonyl peroxynitrate, CH₃S(O)₂OONO₂ (MSPN), and its radical decomposition products CH₃S(O)₂OO· and CH₃S(O)₂O· were studied by ab initio and density functional methods. The dihedral angle around the S–O and the O–O single bond are calculated to be ?70.5° and ?97.8° (B3LYP/6‐311++G(3df,3pd)), respectively. The principal unimolecular dissociation pathways for MSPN were studied using complete basis set (CBS) methods. The reaction enthalpies for the channels CH₃S(O)₂OONO₂→ CH₃S(O)₂OO·+NO₂ and CH₃S(O)₂OONO₂→CH₃S(O)₂O·+NO₃ were computed to be 111.0 and 140.9 kJ/mol, respectively. The enthalpies of formation at 298 K for MSPN and CH₃S(O)₂OO radical were predicted to be ?358.2 and ?281.3 kJ/mol, respectively.     

Ab initio study of the potential energy surface and product branching ratios for the reaction of O(1D) with CH3CH2Br

The potential energy surface of O(¹D) + CH₃CH₂Br reaction has been studied using QCISD(T)/6‐311++G(d,p)//MP2/6‐311G(d,p) method. The calculations reveal an insertion‐elimination reaction mechanism of the title reaction. The insertion process has two possibilities: one is the O(¹D) inserting into C? Br bond of CH₃CH₂Br producing one energy‐rich intermediate CH₃CH₂OBr and another is the O(¹D) inserting into one of the C? H bonds of CH₃CH₂Br producing two energy‐rich intermediates, IM1 and IM2. The three intermediates subsequently decompose to various products. The calculations of the branching ratios of various products formed though the three intermediates have been carried out using RRKM theory at the collision energies of 0, 5, 10, 15, 20, 25, and 30 kcal/mol. CH₃CH₂O + Br are the main decomposition products of CH₃CH₂OBr. CH₃COH + HBr and CH₂CHOH + HBr are the main decomposition products for IM1; CH₂CHOH + HBr are the main decomposition products for IM2. As IM1 is more stable and more likely to form than CH₃CH₂OBr and IM2, CH₃COH + HBr and CH₂CHOH + HBr are probably the main products of the O(¹D) + CH₃CH₂Br reaction. Our computational results can give insight into reaction mechanism and provide probable explanations for future experiments. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical kinetic investigation of thermal decomposition of nitropropane

The thermal decomposition of nitropropane (CH₃CH₂CH₂NO₂) has been investigated at the CBS-QB3 level of theory. The pyrolysis of CH₃CH₂CH₂NO₂ mainly includes the simple bond ruptures mechanism, hydrogen abstraction processes, isomerization and secondary reactions. As a result, for the simple bond ruptures mechanism, the formation of \({\text{CH}}_{3} {\text{CH}}_{2} {\text{CH}}_{2}^{\cdot} +\,^{\cdot}{\text{NO}}_{2}\) products is dominant with the energy barrier of 49.77 kcal mol^?1. The process of H atom on the β–CH₂ abstracted by one O atom of NO₂ moiety in CH₃CH₂CH₂NO₂(CH₃CH₂CH₂NO₂ → CH₃CH=CH₂ + HONO) needs to overcome lower energy barrier than that of the rate-determining step (one of H atom on the α-CH₂ and γ-CH₃ abstracted of reaction) of the other hydrogen abstraction reactions. Therefore, we predict that the corresponding alkenes and HONO are the main products in the hydrogen abstraction reaction of nitroparaffin. Besides, the channel of the CH₃CH₂CHO + HNO formations (CH₃CH₂C(α)H₂NO₂ → CH₃CH₂C(α)H₂ONO → CH₃CH₂CHO + HNO), occurring through the H atom of C(α) abstracted by the N atom of NO₂ moiety after the isomerization reaction from CH₃CH₂CH₂NO₂ to CH₃CH₂CH₂ONO, is favorable in the isomerization secondary reactions. Rate constants and branching ratios are estimated by means of the conventional transition state theory with zero curvature tunneling over the temperature range of 400–1500 K. The calculation shows that the overall rate constant in the temperature of 400–1500 K is mainly dependent on the competitive channels of formations of CH₃CH=CH₂ + HONO and \({\text{CH}}_{3} {\text{CH}}_{2} {\text{CH}}_{2}^{\cdot} +\,^{\cdot}{\text{NO}}_{2}\) The three-parameter expression for the total rate constant is fitted to be k _total = 1.74 × 10^?13 T ^8.20exp(17038.7/T) (s^?1) between 400 and 1500 K.     

Cobalt(II) and nickel(II) complexes of quinoline‐2‐carboxyl­ate

The title complexes, trans‐di­aqua­bis­(quinoline‐2‐carboxyl­ato‐κ²N,O)­cobalt(II)–water–methanol (1/2/2), [Co(C₁₀H₆NO₂)₂(H₂O)₂]·2CH₄O·2H₂O, and trans‐di­aqua­bis­(quinoline‐2‐car­box­yl­ato‐κ²N,O)­nickel(II)–water–methanol (1/2/2), [Ni(C₁₀H₆NO₂)₂(H₂O)₂]·2CH₄O·2H₂O, are isomorphous and contain Co^II and Ni^II ions at centers of inversion. Both complexes have the same distorted octahedral coordination geometry, and each metal ion is coordinated by two quinoline N atoms, two carboxyl­ate O atoms and two water O atoms. The quinoline‐2‐carboxyl­ate ligands lie in trans positions with respect to one another, forming the equatorial plane, with the two water ligands occupying the axial positions. The complex mol­ecules are linked together by hydrogen bonding involving a series of ring patterns which include the uncoordinated water and methanol mol­ecules.     

Tetrakis­(diethyl­amino)­phospho­nium bromide hemihydrate

The structure of the title compound, C₁₆H₄₀N₄P⁺·Br^?·0.5H₂O or [P{N(C₂H₅)₂}₄]Br·0.5H₂O, at 130 K has Z′ = 4 and is ionic, with Br not bonded to P. The P atoms are tetrahedral, with P—N distances in the range 1.628 (2)–1.6400 (19) Å. The N atoms are approximately planar. The water mol­ecules form cyclic hydrogen‐bonded [(H₂O)₂Br₂]^2? units about inversion centers, with O?Br distances in the range 3.425 (2)–3.611 (3) Å.     

Kinetics and Mechanism of the Oxidation of 4-Oxo-4-arylbutanoic Acids by N-bromophthalimide in Aqueous Acetic Acid Medium

The kinetics of oxidation of a series of substituted 4-oxobutanoic acids (Y–C₆H₄COCH₂CH₂COOH: Y = H, OCH₃, CH₃, C₆H₅, Cl, Br or NO₂) by N-bromophthalimide have been studied in aqueous acetic acid medium at 30 °C. The total reaction is second-order, first-order each in oxidant and substrate. The oxidation rate increases linearly with [H⁺], establishing the hypobromous acidium ion, H₂O⁺Br, as the reactive species. A variation in ionic strength has no effect on the reaction rate. The order of reactivity among the studied 4-oxoacids is: 4-methoxy > 4-methyl > 4-phenyl > 4-H > 4-Cl > 4-Br > 3-NO₂. The effect of changes on the electronic nature of the substrate reveals that there is a development of positive charge in the transition state. The activation parameters have been computed from Arrhenius and Eyring plots. Based on the kinetic results, a suitable mechanism has been proposed.     

Transference Numbers in the H2O + NaCl + MgCl2 System at T = 298.15 K,Determined in a Five-Compartment Hittorf Cell

The concentration range of transference number measurements with the Hittorf cell has been extended up to a total concentration of c _T = 3.4 mol·dm^?3 for the H₂O + NaCl + MgCl₂ ternary system at (298.15 ± 0.05) °C. This was achieved with a redesigned Hittorf cell, by dividing each of the anodic/cathodic compartments into two subcompartments: one with a low concentration of H₂O + NaCl for the electrode reaction and another one in contact with the middle compartment with the ternary solution to be measured. Measurements of the transference numbers were also made for the corresponding H₂O + NaCl and H₂O + MgCl₂ binary systems. The experimental details and the results are described.     

Synthesis and Crystal Structure of [La(phen)2(H2O)2(NO3)2]NO3 · 2(phen)(H2O) with phen = 1,10‐phenanthroline

The title compound [La(phen)₂(H₂O)₂(NO₃)₂](NO₃) · 2(phen)(H₂O) with phen = 1,10‐phenanthroline was prepared by the stoichiometric reaction of La(NO₃)₃ · 6 H₂O and 1,10‐phenanthroline monohydrate in a CH₃OH–H₂O solution. The crystal structure (triclinic, P 1 (no. 2), a = 11.052(2), b = 13.420(2), c = 16.300(2) Å, α = 78.12(1)°, β = 88.77(1)°, γ = 83.03(1)°, Z = 2, R = 0.0488, wR² = 0.1028) consists of [La(phen)₂(H₂O)₂(NO₃)₂]²⁺ complex cations, NO₃^– anions, phen and H₂O molecules. The La atom is 10‐fold coordinated by four N atoms of two bidentate chelating phen ligands and six O atoms of two H₂O molecules and two bidentate chelating NO₃^2– ligands with d(La–O) = 2.522–2.640 Å and d(La–N) = 2.689–2.738 Å. The intermolecular π‐π stacking interactions play an essential role in the formation of two different 2 D layers parallel to (001), which are formed by complex cations and uncoordinating phen molecules, respectively. The uncoordinated NO₃^– anions and H₂O molecules are sandwiched between the cationic and phen layers.     

Five solvates of a multicomponent pharmaceutical salt formed by berberine and diclofenac

A multicomponent pharmaceutical salt formed by the isoquinoline alkaloid berberine (5,6‐dihydro‐9,10‐dimethoxybenzo[g]‐1,3‐benzodioxolo[5,6‐a]quinolizinium, BBR) and the nonsteroidal anti‐inflammatory drug diclofenac {2‐[2‐(2,6‐dichloroanilino)phenyl]acetic acid, DIC} was discovered. Five solvates of the pharmaceutical salt form were obtained by solid‐form screening. These five multicomponent solvates are the dihydrate (BBR–DIC·2H₂O or C₂₀H₁₈NO₄⁺·C₁₄H₁₀Cl₂NO₂^?·2H₂O), the dichloromethane hemisolvate dihydrate (BBR–DIC·0.5CH₂Cl₂·2H₂O or C₂₀H₁₈NO₄⁺·C₁₄H₁₀Cl₂NO₂^?·0.5CH₂Cl₂·2H₂O), the ethanol monosolvate (BBR–DIC·C₂H₅OH or C₂₀H₁₈NO₄⁺·C₁₄H₁₀Cl₂NO₂^?·C₂H₅OH), the methanol monosolvate (BBR–DIC·CH₃OH or C₂₀H₁₈NO₄⁺·C₁₄H₁₀Cl₂NO₂^?·CH₃OH) and the methanol disolvate (BBR–DIC·2CH₃OH or C₂₀H₁₈NO₄⁺·C₁₄H₁₀Cl₂NO₂^?·2CH₃OH), and their crystal structures were determined. All five solvates of BBR–DIC (1:1 molar ratio) were crystallized from different organic solvents. Solvent molecules in a pharmaceutical salt are essential components for the formation of crystalline structures and stabilization of the crystal lattices. These solvates have strong intermolecular O…H hydrogen bonds between the DIC anions and solvent molecules. The intermolecular hydrogen‐bond interactions were visualized by two‐dimensional fingerprint plots. All the multicomponent solvates contained intramolecular N—H…O hydrogen bonds. Various π–π interactions dominate the packing structures of the solvates.     

(M)‐ and (P)‐8‐[(1S,2R)‐2‐hydroxy‐1‐methyl‐2‐phenylethyl]‐8‐methyl‐8,9‐dihydro‐7H‐dinaphth[2,1‐c:1′,2′‐e]azepinium bromide solvates

The title compounds are diastereoisomers with antipodean axial chirality. The M isomer crystallizes as a (1/3) acetone solvate, C₃₂H₃₀NO⁺·Br^?·3C₃H₆O, while the P isomer crystallizes as a (1/1) di­chloro­methane solvate, C₃₂H₃₀NO⁺·Br^?·CH₂Cl₂. In each structure, O—H?Br hydrogen bonds link the cations and anions to give ion pairs. The seven‐membered azepinium ring adopts the usual twisted‐boat conformation and its ring strain causes a slight curvature of the plane of each naphthyl ring.     

Theoretical study on the gas phase reaction mechanism of acetylene with nitrous oxide

The reaction mechanism of C₂H₂ and N₂O on the singlet potential energy surface is investigated in this study, at the B3LYP/6-311++G(3df,3pd), MP2/6-311++G(d,p), and CCSD(T) levels of theory. We have obtained three kinds of products in both methods, B3LYP and MP2, which have enough thermodynamic stability. The results reveal that the product P1, CH₂CO + N₂, is spontaneous and exothermic with ?86.176 and ?83.149 kcal/mol in Gibbs free energy and enthalpy of reaction at the MP2 level, respectively. Hence, the product P1 is thermodynamically the most favored adduct of the C₂H₂ + N₂O gas phase reaction at atmospheric pressure and 298.15 K temperature.     

Semiconductor Photocatalysts for Non-oxidative Coupling,Dry Reforming and Steam Reforming of Methane

Methane is one of the promising alternatives of petroleum, which should be used for not only a fuel but also a resource for hydrogen and more useful chemicals as with the petroleum. However, the selective methane conversion to them is still difficult in contrast to the combustion. Three types of photocatalytic reactions for methane conversion, i.e., the photocatalytic non-oxidative coupling of methane (2CH₄ → C₂H₆ + H₂), the photocatalytic dry reforming of methane (CH₄ + CO₂ → 2CO + 2H₂) and the photocatalytic steam reforming of methane (CH₄ + 2H₂O → 4H₂ + CO₂), can take place around room temperature or at a mild condition such as 473 K using photoenergy and semiconductor photocatalyst. In the present short review, the details of each photocatalytic reaction and the design concept of the semiconductor photocatalysts for each photocatalytic methane conversion were summarized and discussed.