Maoxia He

Mechanical and Kinetic Studies of the Formation of Polyhalogenated Dibenzo-p-dioxins from Hydroxylated Polybrominated Diphenyl Ethers and Chlorinated Derivatives

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs),which may be generated from PBDEs, are more toxic than their matrix and have been detected in organisms. In this article, we have focused on the gas phase formation of polyhalogenated dibenzo-p-dioxins from several OH-PBDEs and their chlorinated derivatives. All of the geometries and frequencies are calculated at the MPWB1K/6-31+G(d,p) level of theory. The single point energy is obtained at the MPWB1K/6-311+G(3df,2p) level. Rate constants of each step have been calculated over a wide range of 200-2000 K using the canonical variational transition state (CVT) theory with small curvature tunneling (SCT) contribution. The rate equations are shown through Arrhenius formulas. The presence of chlorine atoms increases the reaction barrier for the formation of major products.

Quantum chemical study of alcoholysis mechanism of 1,2-thiazetidine 1,1-dioxide

The alcoholysis of 1,2-thiazetidine 1,1-dioxide has been investigated using ab initio and density functional theory at HF/6-31G*, MP2/6-31G*//HF/6-31G* and B3LYP/6- 31G* levels. The geometries, energies and frequencies of all stationary points were calculated in detail. Solvent effects have been considered by means of a polarizable continuum model (PCM). Our results indicate the alcoholysis of 1,2-thiazetidine 1,1-dioxide proceeds via concerted mechanism and stepwise mechanism. In the stepwise mechanism, two possible reaction pathways can be followed whilst one possible reaction pathway can be followed in the concerted mechanism. The most favorite pathway for alcoholysis of 1,2-thiazetidine 1,1-dioxide was found.

Theoretical investigation on the mechanisms and kinetics of OH-initiated photooxidation of dimethyl phthalate (DMP) in atmosphere

The atmospheric OH-initiated degradation mechanisms of dimethy phthalate (DMP) are analyzed at the MPWB1K/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) level of theory. The principal products detected experimentally are confirmed by this study while several major intermediates are reported for the first time. Additionally, the pathway scheme of hydroxylation reaction of DMP is proposed. The results about initial steps indicate that hydroxyl radical is most likely to be added to the ortho-carbon atom among additional reactions, while H atoms in methyl group are the most favorable to be abstracted by the OH radical. The rate constants of the elementary reactions over the temperature of 200-400 K were deduced using RRKM theory. The overall rate constant of the title reaction is 1.18×10(-12) cm(3) molecule(-1) s(-1) at 298 K and 760 Torr while H abstraction reactions predominate. According to the rate constants given at different temperatures, the Arrhenius equation is fitted. The atmospheric half life of DMP with respect to OH is estimated to be 6.8 days.

Mechanistic and kinetic study on the ozonolysis of n-butyl vinyl ether, i-butyl vinyl ether and t-butyl vinyl ether

Density functional theory (DFT) and ab initio method are employed to elucidate the mechanisms for O(3)-initiated oxidation of n-butyl vinyl ether (n-BVE) and its isomers (i-BVE and t-BVE). For each BVE, the reactions proceed via O(3) cycloaddition resulting in the formation of primary ozonides (POZs) and then two self-decomposition pathways of POZs are followed. Major products are identified to be formaldehyde and butyl formates (CH(3)CH(2)CH(2)CH(2)OCHO for n-BVE, (CH(3))(2)CHCH(2)OCHO for i-BVE and (CH(3))(3)COCHO for t-BVE). The total and individual rate constants for main product channels have been calculated using the modified multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) approach. At 298 K and 101 kPa, the calculated total rate constants are 2.50×10(-16), 3.41×10(-16) and 4.17×10(-16) cm(3) molecule(-1) s(-1) for n-BVE+O(3), i-BVE+O(3) and t-BVE+O(3), respectively, which are in perfect agreement with experimental results. The total rate coefficients are almost pressure independent in the range of 0.001-101 kPa but obviously positive temperature dependent over the whole study temperature range (200-400 K). Also, the favorable reaction pathways have been determined through the estimation of branching ratios. Moreover, the influence of alkoxy group structure on the reactivity of vinyl ethers was examined.

Computational study on the mechanisms and rate constants of the Cl-initiated oxidation of methyl vinyl ether in the atmosphere.

The Cl-initiated oxidation reactions of methyl vinyl ether (MVE) are analyzed by using the high-level composite method CBS-QB3. Detailed chemistry for the reactions of MVE with chlorine atoms is proposed according to the calculated thermodynamic data. The primary eight channels, including two Cl-addition reactions and six H-abstraction reactions, are discussed. In accordance with the further investigation of the two dominant additional routes, formyl chloride and formaldehyde are the major products. Over the temperature range of 200-400 K and the pressure range of 100-2000 Torr, the rate constants of primary reactions are calculated by employing the MESMER program. H-abstraction channels are negligible according to the value of rate constants. During the studied temperature range, the Arrhenius equation is obtained as ktot = 5.64 × 10(-11) exp(215.1/T). The total rate coefficient is ktot = 1.25 × 10(-10) cm(3) molecule(-1) s(-1) at 298 K and 760 Torr. Finally, the atmospheric lifetime of MVE with respect to Cl is estimated to be 2.23 h.

Computational study on the mechanisms and rate constants of the OH-initiated oxidation of ethyl vinyl ether in atmosphere.

The hydroxylation reactions of ethyl vinyl ether (EVE) in the present of O2 and NO are analyzed by using MPWB1K/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) level of theory. According to the calculated thermodynamic data, the detailed reaction mechanisms of EVE and OH are proposed. All of the ten possible reaction pathways are discussed. The major products of the title reaction are ethyl formate and formaldehyde, which is in accordance with experimental detection. The rate constants of the primary reactions over the temperature of 250-400K and the pressure range of 100-2000Torr are computed by employing MESMER program. At 298K and 760Torr, OH-addition channels are predominate and the total rate constant is ktot=4.53×10(-11)cm(3)molecule(-1)s(-1). The Arrhenius equation is obtained as ktot=6.27×10(-12)exp(611.5/T), according to the rate constants given at different temperatures. Finally, the atmospheric half life of EVE with respect to OH is estimated to be 2.13h.

THEORETICAL STUDY OF OH-INITIATED ATMOSPHERIC OXIDATION FOR PROPYL VINYL ETHER

This paper reports a theoretical study on the reaction of propyl vinyl ether (PVE, CH3CH2CH2OCH=CH2) with OH radicals in the presence of O2 and NOx. The reaction pathway has been studied with the density functional theory (DFT/B3LYP) at the 6-31G* level. The total energies of all geometries are corrected at the MP2/6-311+G** level. The profile of the potential energy surface was constructed. The possible channels involved in the reaction were discussed. The results show that six product pathways are energetically feasible for the degradation of PVE initiated by OH radicals in the atmosphere. The main products for this degradation reaction are propyl formate, formaldehyde, and glycolic acid propyl ester in which propyl formate and formaldehyde are mainly from the OH addition to C5 atom.

Computational investigations on the electronic and structural properties of the unsaturated silylenoid HP=SiLiF

The structures of unsaturated silylenoid HP=SiLiF were studied by density functional theory at the B3LYP/6-311+G(d,P) level. Four equilibrium structures, the three-membered ring (1), the four-membered ring (2), the “classical” silane (3), and the linear (4) structures, were located. Their energies are in the order of 4 > 3 > 1 > 2. To exploit the stability of HP=SiLiF, the insertions reaction of 2 and HP=Si into C-Cl have been investigated, respectively. The results show that the insertion of HP=Si is more favorable. To compare with the saturated silylenoid, the insertion reaction of H2SiLiF was also investigated. The calculations indicate that the insertion of HP=SiLiF (2) is more favorable. The unsaturated siylenoid HP=SiLiF has similar reaction characters to saturated silylenoid H2SiLiF and silylene HP=Si.

Electronic structures of bis- and monothiophene complexes with Fe, Co, Ni: a density functional theory study.

A density functional theory study for the bis- and monothiophene complexes of Fe, Co, and Ni (MT2 and MT, T = thiophene, M = Fe, Co, Ni) was performed to understand their coordination geometries, bonding properties, vibration spectra and singlet excited state spectra. The typical metal coordination exists in the complexes. The Fe-thiophene coordination has the highest stability, with Ni-thiophene being the second highest, and Co-thiophene the lowest. Bisthiophene complexes of Co and Ni prefer to homolytically dissociate to their monothiophene ones and free thiophene. Frequency calculation shows that the ligand-M-ligand asymmetric stretching vibration in bisthiophene complexes shows a strong absorption, at 435.2, 495.7, and 383 cm(-1) for Fe(eta4-T)2, Co(eta2-T)2 and Ni(eta2-T)2, respectively. The M-S stretching vibration in monothiophene complexes shows a strong absorption in the far-infrared region, at 209, 156, and 150 cm(-1) for Fe(eta4-T), Co(eta4-T) and Ni(eta5-T), respectively. The excited state spectra indicate that the characteristic absorption wavelengths of the complexes have a red shift of more than 12.40 eV compared to free thiophene, at 3.54, 1.64, 3.83, 2.75, 1.43, and 2.58 eV for Fe(eta4-T)2, Co(eta2-T)2, Ni(eta2-T)2, Fe(eta4-T), Co(eta4-T), and Ni(eta5-T), respectively.

Theoretical study on the mechanism of the gas phase reaction of methoxybenzene with ozone

Methoxybenzene (MB), is seen as a potential air pollutant which may cause environmental issues in the troposphere. Nevertheless, our understanding of its gas phase reaction is extraordinarily limited. In this study, the quantum chemical methods [M06-2X/aug-cc-pVDZ//M06-2X/6-31+g(d,p)] and Rice–Ramsperger–Kassel–Marcus (RRKM) theory are utilized in investigating the detailed mechanisms and rate constants for the ozonolysis of MB for the first time. The results show that O3-addition to the methoxy-substituted carbon dominates the entrance channel of MB with ozone and the total rate coefficient of the title reactions is calculated to be 2.67 × 10−21 cm3 per molecule per s at 298 K and 1 atm. The bimolecular rate constants show positive dependence on temperature (200–400 K) and negative dependence on pressure (10−3, 10−2, 10−1 and 1 atm). Moreover, the atmospheric lifetime of MB determined by O3 is available concerning the typical concentration of O3. This work aims to provide reference data for future experimental research on MB.