Multicomponent QM study on the reaction of HOSO + NO2 with H2O: Nuclear quantum effect on structure and reaction energy profile

The hydrogen transfer reaction in the reaction of HOSO + NO₂ with and without H₂O have been investigated using multicomponent quantum-mechanics method, which can directly take nuclear quantum effect (NQE) of light nuclei into account. For the case of the reaction without H₂O, our calculation reveals that the reaction leading to trans-HONO is preferred. For the reaction with H₂O, water-non-mediated and water-mediated (hydrogen-relay) hydrogen transfer mechanism are investigated. The NQE of hydrogen nucleus lowers the relative energy of the stationary point structures and reduces the activation barrier of the reactions. The largest stabilization is found in the transition state structure of the hydrogen-relay type reaction. H/D isotope effects for the reactions are also analyzed. In particular, H/D isotope effect on the activation barrier is analyzed in detail with the aid of the active strain model.     

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 H<Subscript>2</Subscript>S activation by PtCH<Subscript>2</Subscript><Superscript>+</Superscript> in the gas phase

The reaction mechanism of the gas-phase PtCH₂ ⁺ with H₂S has been systematically investigated on the doublet and quartet potential energy surfaces at BPW91/6-311++G(2d, p)∪ SDD level. The Pt in PtCH₂ ⁺ prefers to attack S–H bond in H₂S. For PtCH₂ ⁺ + H₂S reaction, the potential energy surfaces (PESs), including three reaction pathways of hydrogen (including one and two hydrogen elimination) and methane elimination, have been explored and characterized. By contrast with hydrogen elimination, methane elimination reaction channel is energetically favorable, which is in good agreement with the experimental observation. The optimal S–H bond activation is the first step, followed by cleavage of Pt–C and Pt–S bond. About the path a and b, the lowering of activation barrier is mainly caused by the more stabilizing transition state interaction \(\varDelta E_{\text{int}}^{ \ne }\), which is the actual interaction energy between the deformed reactants in the transition state.     

Mechanism of the reaction NO + H<Subscript>2</Subscript> on the Pt(100)-hex surface under conditions of the spatially nonuniform distribution of reacting species

The interaction of hydrogen with NO_ads/1 × 1 islands produced by NO adsorption on the reconstructed surface Pt(100)-hex was studied by high-resolution electron energy loss spectroscopy (HREELS) and the temperature-programmed reaction (TPR) method. The islands are areas of the unreconstructed surface Pt(100)-1 × 1 saturated with NO_ads molecules. The hexagonal phase around these islands adsorbs much more hydrogen near room temperature than does the clean Pt(100)-hex surface. It is assumed that hydrogen is adsorbed on the hexagonal surface areas that are adjacent to, and are modified by, the NO_ads/1 × 1 islands. The reaction of adsorbed hydrogen atoms with NO_ads takes place upon heating and has the character of so-called surface explosion. The TPR peaks of the products of this reaction—nitrogen and water—occur at T _des ～ 365–370 K, their full width at half-maximum being ～5–10 K. In the case of the NO_ads/1 × 1 islands preactivated by heating in vacuo above the NO desorption onset temperature (375–425 K), after the admission of hydrogen at 300 K, the reaction proceeds in an autocatalytic regime and the product formation rate increases monotonically at its initial stage. In the case of activation at 375 K, during the initial, slow stage of the reaction (induction period), hydrogen reacts with nitric oxide molecules bound to structure defects (NO_def). After activation at 425 K, the induction period is characterized by the formation and consumption of imido species (NH_ads). It is assumed that NH_ads formation involves N_ads atoms that have resulted from NO_ads dissociation on defects upon thermal activation. The induction period is followed by a rapid stage of the reaction, during which hydrogen reacts with NO_{1 × 1} molecules adsorbed on 1 × 1 areas, irrespective of the activation temperature. After the completion of the reaction, the areas of the unreconstructed phase 1 × 1 are saturated with adsorbed hydrogen. The formation of H_ads is accompanied by the formation of a small amount of amino species (NH_2ads).     

Energy barriers to gas-phase unimolecular decomposition of trinitrotoluenes

Alternative versions of gas-phase unimolecular decomposition of six isomeric trinitrotoluenes, in particular homolytic dissociation of C_arom–NO₂ and C_arom–CH₃ bonds, nitro–nitrite rearrangement, intramolecular hydrogen transfer from the methyl group to nitro group with formation of aci-trinitrotoluenes, and formation of various bicyclic intermediates, have been simulated at the B3LYP/6-31+G(2df,p) level of theory. Except for 3,4,5-trinitrotoluene, the most energetically favorable for all other examined trinitrotoluenes is intramolecular hydrogen transfer. 3,4,5-Trinitrotoluene preferentially decomposes via formation of [6 + 4]-bicyclic intermediates or homolytic dissociation of the C_arom–NO₂ bond.     

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.     

Vibrational spectra and structure of trinitromethane

The vibrational spectrum of trinitromethane was interpreted in terms of the additive interatomic interaction model on the basis of experimental infrared and Raman spectra of HC(NO₂)₃, DC(NO₂)₃, HC(¹⁵NO₂)₃ and normal coordinate analysis. The frequency assignment results were used in discussing its structure. It was shown that the symmetry of trinitromethane is below C₃ in the liquid state.     

Dual-level direct dynamics studies on the reactions of tetramethylsilane with chlorine and bromine atoms

The multiple-channel reactions Cl + Si(CH₃)₄ and Br + Si(CH₃)₄ are investigated by direct dynamics method. The minimum energy path 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 channel are calculated by the improved canonical variational transition state theory with small-curvature tunneling correction over the temperature range 200–3,000 K. The theoretical three-parameter expression k ₁(T) = 9.97 × 10^?13 T ^0.54exp(613.22/T) and k ₂(T) = 1.16 × 10^?17 T ^2.30exp(?3525.88/T) (in unit of cm³ molecule^?1 s^?1) are given. Our calculations indicate that hydrogen abstraction channel is the major channel due to the smaller barrier height among feasible channels considered.     

Synthesis and nitration of 3-R-4-(2,2,2-trinitroethyl)aminofuroxans

Simple methods for the synthesis of 3-R-4-(2,2,2-trinitroethyl)aminofuroxans were developed based on the Mannich reaction of N,N′-bis(3-R-furoxan-4-yl)methylenediamines with trinitromethane or 3-R-4-aminofuroxans with trinitroethanol or with CH₂O and trinitromethane. The Mannich bases obtained were studied in the nitration reaction, which showed their ability to form nitramines depending on substituents on the furoxan ring.     

A Theoretical Investigation on Intramolecular Hydrogen Bond: The ESIPT Mechanism of dmahf Sensor

The properties of intramolecular hydrogen bond of a new photochemical sensor 4′-N,N-dimethylamino-3-hydroxyflavone (dmahf) has been investigated in detail. Using Atoms-In-Molecule method, we have demonstrated that the intramolecular hydrogen bond was formed in the ground state (S₀ state). The calculated dominating bond lengths and angles involved in hydrogen bond demonstrates that the intramolecular hydrogen bond can be strengthened in the first excited state (S₁ state). In addition, the variation of hydrogen bond of dmahf has been also testified based on infrared vibrational spectra. Further, hydrogen bonding strengthening manifests the tendency of excited state intramolecular proton transfer process. According to the calculated results of potential energy curves along O–H coordinate, the potential energy barrier of about 7.49 kcal/mol is discovered in the S₀ state. However, a lower potential energy barrier of 1.61 kcal/mol has been found in the S₁ state, which demonstrates that the proton transfer process is more likely to happen in the S₁ state than the S₀ state. In other words, the proton transfer reaction can be facilitated based on the photoexcitation effectively. In turn, through the process of radiative transition, the proton-transfer form dmahf-keto regresses to the ground state with the fluorescence of 578 nm.     

The C—H⋯O hydrogen bond. An ab initio study of nitrosomethane and its hydrogen bonded dimer

In order to study the short C—H?O contact which has been found in several nitroso compounds, a series of ab initio calculations have been performed on nitrosomethane and it's cyclic “hydrogen bonded” dimer. A potential function for the C—H?O contact has been found and the effect of this contact upon the NO and CN bonds has been studied. The potential is shallow with a minimum of only ?2.65 kcal mol^?1 for each contact and the equilibrium C?O distance is 3.524, A. These results indicate that the C—H?O bond is better described as a van der Waal's type contact than a hydrogen bond. The equilibrium length of the NO bond (R_NO) changes in a regular manner with variations in the C?O (R_HYD) distance, i.e. when R_HYD becomes shorter R_NO becomes longer. However, the variations in the CN bond lengths, which in the nitrosomethane monomer molecule is a long and weak bond, are anomalous.     

ε-六硝基六氮杂异伍兹烷(CL-20)热解机理的理论研究

运用量子化学中非限制性Hartree-Fock自洽场(UHF-SCF) PM3分子轨道(MO)方法, 计算研究六硝基六氮杂异伍兹烷(HNIW或CL-20)的最稳定ε晶型化合物的气相热解引发反应. 求得可能的四种不同热解反应通道的过渡态、活化能和位能曲线, 发现其热解引发步骤为五元环上侧链N—NO₂键的均裂. 在过渡态附近相关原子电荷发生突变.     

Molecular structures of trinitromethane derivatives

The molecular structures of trinitromethane derivatives XC(NO₂)₃ (X = F, Cl, Br, NC, NF₂, N₃) were studied using the density functional approach. The rules for changing the configurations of substituents in these compounds were revealed. Acceptability of the method employed for the calculations of trinitromethane derivatives is discussed.     

Microwave-assisted dissolution of ceramic uranium dioxide in TBP–HNO3 complex

Microwave-assisted dissolution of ceramic uranium dioxide in tri-n-butyl phosphate (TBP)–HNO₃ complex was investigated. The research on dissolution of ceramic uranium dioxide in TBP–HNO₃ inclusion complex under microwave heating showed the efficiency of the use of this method. Nitric acid present in the inclusion complex participates both dissolution of UO₂, and oxidation of U(IV)–U(VI), the resulting UO₂(NO₃)₂ extracted with tri-n-butyl phosphate. Dissolution rate depends on both temperature of microwave dissolution process, and concentration of nitric acid present in the inclusion complex. The most intensive dissolution process is when the concentration of nitric acid ≥2 mol/L and the temperature of 120 °C. From the experimental data obtained by two kinetic models activation energies were calculated. At the average activation energy of UO₂ dissolution in TBP–HNO₃ complex equal 70 kJ/mol, and reaction order is close to one, i.e. the reaction takes place in an area close to kinetic.     

Aquabromo(6‐carboxypyridine‐2‐carboxylato‐O,N,O′)mercury(II)

The title compound, [HgBr(C₇H₄NO₄)(H₂O)], was obtained by the reaction of an aqueous solution of mercury(II) bromide and pyridine‐2,6‐di­carboxylic acid (picolinic acid, dipicH₂). The shortest bond distances to Hg are Hg—Br 2.412 (1) Å and Hg—N 2.208 (5) Å; the corresponding N—Hg—Br angle of 169.6 (1)° corresponds to a slightly distorted linear coordination. There are also four longer Hg—O interactions, three from dipicH^? [2.425 (4) and 2.599 (4) Å within the asymmetric unit, and 2.837 (4) Å from a symmetry‐related mol­ecule] and one from the bonded water mol­ecule [2.634 (4) Å]. The effective coordination of Hg can thus be described as 2+4. The mol­ecules are connected to form double‐layer chains parallel to the y axis by strong O—H?O hydrogen bonds between carboxylic acid groups of neighbouring mol­ecules, and by weaker hydrogen bonds involving both H atoms of the water mol­ecule and the O atoms of the carboxylic acid groups.     

Photochemical Reaction Mechanisms of 2‐Nitrobenzyl Compounds in Solution,I. 2‐Nitrotoluene: Thermodynamic and Kinetic Parameters of the aci‐Nitro Tautomer

The largely reversible, light‐induced tautomerization of 2‐nitrotoluene ( 1 ) to the quinonoid aci‐nitro tautomer aci‐ 1 was studied by flash photolysis as a benchmark for comparison with the widely used nitrobenzyl phototriggers (`caged compounds'). The pH‐rate profile for the decay of aci‐ 1 in aqueous solution exhibits downward curvature at pH 3 – 4, which is attributed to pre‐equilibrium ionization of the nitronic acid aci‐ 1 to its anion 1 ⁻ (pK_a=3.57). Two regions of upward curvature, at pH ca. 6 and <0 (H₀≈−1), each indicate a change in the reaction mechanism. The elementary reactions that dominate between the curved regions are assigned on the basis of kinetic isotope effects and the observation of general acid catalysis: Hydronium ions regenerate 2‐nitrotoluene by C‐protonation of 1 ⁻ in the pH range of 0 – 6, and H₂O is the proton source at pH>6. A hird, irreversible Nef‐type isomerization of aci‐ 1 prevails in highly acidic solutions (pH<0). The equilibrium constant for the thermal tautomerization of 1 to aci‐ 1 is estimated as pK_T=17.0±0.2 based on kinetic data.     

Release of nitric oxide from nitrated fatty acids: Insights from computational chemistry

Nitrated fatty acids (NO₂‐FAs) exhibit a variety of important biological attributes, including a nitric oxide (˙NO) donor and a cell‐signaling molecule. We investigated the mechanisms of fatty‐acid nitration, and the release of ˙NO from NO₂‐FAs. NO₂‐FAs are formed effectively by the addition of ˙NO₂, followed by either hydrogen abstraction or addition of a second NO₂. The latter reaction results in a vicinal nitronitrite ester form of FA, which isomerizes into vicinal nitrohydroxy FA via hydronium ion catalysis. The nitrohydroxy FAs exist in equilibria with NO₂‐FAs. Nitration of conjugated linoleic acid (cLA) was proved to be significantly more efficient than that of LA. In a nonaqueous environment, release of ˙NO from nitrite ester (ONO‐FA) was facilitated by ˙NO₂. Furthermore, the release of ˙NO from NO₂‐cLA is the most favorable in the nitrite ester mechanism. In an aqueous environment, the modified Nef reaction was shown to be feasible. In addition, the release of ˙NO from 10‐ and 12‐NO₂‐LA involves a larger reaction barrier and is more endergonic than those from 9‐ and 13‐NO₂‐LA.     

Halogen migration vs. hydrogen halogenide elimination in reactions of 1-chloro-2,2,2-trifluoroethansulfonyl chloride and 1,2,2,2-tetrafluoroethansulfonyl fluoride with amines: theoretical and experimental investigation

A simple and useful method has been proposed for preparing of 1-chloro-2,2,2-trifluoroethan sulfonylchloride. By aminolysis of 1-chloro-2,2,2-trifluoroethansulfonylchloride the chlorine migration proceeds forming the corresponding salts of 1,1-dichloro-2,2,2-trifluoroethansulfinic acid. This process as well as the alternative reaction, elimination of hydrogen halogenide, has been studied using quantum chemistry (DFT and MP2) methods. As the calculation data indicate, an intermediately formed anion undergo intramolecular chlorine migration via a three-membered cyclic transition state. The latter is characterized by the low activation energy (ΔE = 27.0 kcal/mol). The barrier of activation in the case of 1,2,2,2-tetrafluoroethansulfonylfluoride is considerably higher (ΔE = 41.6 kcal/mol). The structures of the 1,1-dichloro-2,2,2-trifluoroethan sulfinic acid and 1,1,2,2,2-pentafluoroethansulfinic acid anions can be considered as donor-acceptor complexes of perhalogenoalkyl anions with SO₂.     

The removal of styrene using a dielectric barrier discharge (DBD) reactor and the analysis of the by-products and intermediates

As a kind of volatile organic compound, styrene is a typical industrial pollutant with high toxicity and odorous smell. In this study, the removal of malodorous styrene simulation waste gas was carried out in a self-made wire-tube dielectric barrier discharge reactor. The decomposition efficiency of the reaction was investigated under different applied voltages and flow rates. The results showed that nearly 99.6 % of styrene could be removed with a concentration of 3,600 mg/m³ and the applied voltage of 10.8 kV. However, the selectivity of CO₂ and CO showed that the mineralization efficiency of styrene was less than 25 %. The by-products of the reaction, including O₃, NO _x and other intermediates, were also detected and analyzed under different applied voltages. The relationships between the applied voltage and the quantity of final product (CO₂) and by-products (intermediate organics, NO _x , O₃) were investigated. The reaction mechanism was also described according to the bond energy and the intermediates that formed.     

A hydrogen‐bonded heterodimer of 1‐(4‐hexyloxyphenyl)pyridin‐4(1H)‐one with 4‐cyano­benzoic acid

The two components of the title heterodimer, C₁₇H₂₁NO₂·C₈H₅NO₂, are linked end‐to‐end via O—H⋯O(=C) and C—H⋯O(=C) hydrogen‐bond inter­actions. Additional lateral C—H⋯O inter­actions link the dimers in a side‐by‐side fashion to produce wide infinite mol­ecular ribbons. Adjacent ribbons are inter­connected viaπ–π stacking and C—H⋯π(arene) inter­actions. This structure represents the first evidence of robust hydrogen‐bond formation between the moieties of pyridin‐4(1H)‐one and benzoic acid.