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1.
J Hazard Mater ; 386: 121636, 2020 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-31753671

RESUMO

The elimination mechanisms and the dynamics of 2,5-dimethylbenzoquinone/2,6-dimethylbenzoquinone are performed by DFT under the presence of ·OH radical and TiO2-clusters. The rate coefficients, calculated within the atmospheric and combustion temperature range of 200-2000 K, agree well with the experimental data. The subsequent reactions including the bond cleavage of quinone ring, O2 addition or abstraction, the reactions of peroxy radical with NO yielding the precursor of organic aerosol are studied. Gaseous water molecule plays an important role in the transformation of alkoxy radical and exhibits a catalytic performance in the enol-ketone tautomerism. The lifetimes of 2,5-dimethylbenzoquinone/2,6-dimethylbenzoquinone are about 12.04-12.86 h at 298 K, which are in favor of the medium range transport of them in the atmosphere. Significantly, the water environment plays a negative role on the ·OH-degradation of dimethylbenzoquinone. Compared to the quinone ring, 2,5-dimethylbenzoquinone onto (TiO2)n clusters (n = 1-6) is easier to be absorbed by TiO2-clusters through its oxygen site because of its strong chemisorption, which indicates that TiO2-clusters are capable of trapping dimethylbenzoquinones effectively. The water environment could weaken the adsorption of 2,5-dimethylbenzoquinone onto (TiO2)n clusters (n = 1-6) by increasing the adsorption energy. This work reveals the removal of dimethylbenzoquinones and the formation of organic aerosol under polluted environments.

2.
Sci Total Environ ; 699: 134190, 2020 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-31670037

RESUMO

The initial reactions of organics with •OH are important to understand their transformations and fates in advanced oxidation processes in aqueous phase. Herein, the kinetics and mechanism of •OH-initiated degradation of ciprofloxacin (CIP), an antibiotic of fluoroquinolone class, are obtained using density functional and computational kinetics methods. All feasible mechanisms are considered, including H-abstraction, •OH-addition, and sequential electron proton transfer. Results showed that the H-abstraction is the dominant reaction pathway, and the product radicals P7H, P9H, and P10H are the dominating intermediates. The aqueous phase rate coefficients for the •OH-triggered reaction of ciprofloxacin are calculated from 273 K to 323 K to examine the temperature dependent effect, and the theoretical value of 6.07 × 109 M-1 s-1 at 298 K is close to the corresponding experimental data. Moreover, the intermediates P7H, P9H, and P10H could easily transform to several stable products in the presence of O2, HO2•, and •OH. The peroxy radical, which is generated from the incorporation of H-abstraction product radicals (P7H, P9H, and P10H) with O2, prefers to produce HO2• into the surrounding through direct concerted elimination rather than the indirect mechanism. In addition, the peroxy radical could react with HO2• via triplet and singlet routes, and the former is more favorable due to its smaller barrier compared with the latter. The hydroxyl-substituted CIP has higher activity than its parent compound in their reactions with •OH due to its lower barrier and faster rate. In addition, the -NHC(O)-containing compound IM3-P10-H-4 is harmful to aquatic fish and is the primary product in the •OH-rich environment according to the ecotoxicity assessment computations. This study can improve our comprehension on CIP transformation in complex water environments.

3.
J Mol Model ; 25(12): 346, 2019 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-31729561

RESUMO

The nitrate esters are important components of double-base propellants. Aromatic amines are recommended as the stabilizers to delay the decomposition of nitrate esters and increase their storage time. The decomposition mechanisms of alkyl, alkoxy dinitrate, and poly-fluoride nitrate esters and the stabilizing effect of aromatic amines including new designed phenols are studied at the level of B3LYP/6-31G**. Alkyl and alkoxyl dinitrate esters are likely to be transformed by hydrogen abstraction, which is consistent with that of mononitrate and trinitrate esters. However, for poly-fluoride nitrate esters, NO2 catalyzed self-decomposition is preferred. In addition, comparing with mononitrate and trinitrate esters, the order of their stability is mononitrates > dinitrates > trinitrates. Poly-fluoride nitrate esters have a poorer stability than non-fluorinated nitrate esters. Comparing with parent nitrate esters, the stability of new designed poly-fluoride oxygen-containing nitrate esters is slightly improved. Aromatic amines including new designed phenols are effective stabilizers of nitrate esters, especially when introduced hydroxyl in the para position, can enhance the effects of stabilizers. The rate constants for the decomposition of nitrate esters and the bimolecular reaction between stabilizers and NO2 are calculated by using traditional transition state theory. Graphical abstractComparison between the reaction energy barrier of nitrate esters and stabilizers with NO2.

4.
Environ Sci Process Impacts ; 21(12): 2080-2092, 2019 Dec 11.
Artigo em Inglês | MEDLINE | ID: mdl-31599916

RESUMO

The oxidation mechanism of 4-hydroxy-3-hexanone (CH3CH2C(O)CH(OH)CH2CH3) initiated by NO3 radicals in the nighttime is investigated systematically by applying quantum theoretical methods. According to thermodynamic research, the process of H-abstraction on the -CH- group adjacent to the hydroxyl group is the most dominant pathway with the lowest activation energy. The analysis of Mulliken charge charts and molecular electrostatic potential maps illustrate that C-H bonds are the active sites of the reaction, and the calculated C-H bond dissociation energy of the CH3CH2C(O)CH(OH)CH2CH3 molecule further confirms that α-CH is the most easily activated. Individual rate constants for five H-abstraction pathways are calculated by canonical variational theory coupled with small curvature tunneling method over the temperature range of 260-330 K, and the branching ratios are also evaluated. A total rate constant of 1.18 × 10-15 cm3 per molecule per s is obtained at 298 K, which is in good agreement with the reported experimental value. A negative temperature dependence is observed in the titular reaction. The subsequent degradation processes of the advantageous product alkyl radical (CH3CH2C˙(OH)COCH2CH3) are carried out in a NO-rich environment, and propionic acid, NO2 and ozone are obtained as the major final products. The nighttime atmospheric lifetime of 4-hydroxy-3-hexanone is estimated to be around 19 days, indicating that it has impact at night. The titular reaction rate constants are fitted to a three-parameter Arrhenius formula.

5.
J Mol Graph Model ; 93: 107453, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31569010

RESUMO

The nocturnal reactions of CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 initiated by NO3 radicals are important sources of alkyl radicals and nitric acids. In this paper, the thermodynamics and kinetics of CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 induced by NO3 radical in gas phase are studied in detail by BHandHLYP method combined with 6-311G(d,p) basis set, and the single point correction is calculated by relatively accurate CCSD(T) method. In the temperature range of 200-400 K, the rate constants of title reactions are fitted to the three-parameter Arrhenius formula: k1 = 1.13 × 10-40T9.24exp(1675.99/T) k2 = 2.23 × 10-23T2.81exp(-4476.24/T) k3 = 5.63 × 1043T-19.20exp(-9344.12/T) All the rate constants calculated by the canonical variational transition state theory and the small curvature tunneling are basically consistent with the limited experimental data. By comparing the reaction rate constants of ethyl ether and its isomer methyl propyl ether with NO3 radical at 293 ±â€¯2 K, the higher the symmetry is, the faster the reaction rate of ether is. Thermodynamic calculations and kinetic data of the title reactions indicate that the H-abstraction reactions at the -OCH2- sites are the main reaction pathways. The thermodynamic and kinetic data of the reaction CH3CH2OCH2CH3, CHF2CF2OCH2CF3 with NO3 radical, showing that the reaction activity could be reduced due to the addition of fluorine atoms, which is further verified by the enthalpies, Gibbs free energies of the title reactions and C-H bond dissociation energies of the CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 molecules. The reaction thermodynamics and kinetics are determined, and the formation mechanisms of the products are proposed, which are crucial to determine the influence of CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 on air quality, as well as its atmospheric lifetime and durability. The atmospheric lifetimes of CH3CH2OCH2CH3, CHF2CF2OCH2CF3 and CF3CH2OCH3 are evaluated in the NO3-concentration range of 5 × 108-2 × 109 molecule cm-3 to fully consider the effects of different regions on their nocturnal migration. The radiation efficiency and global warming potentials (GWPs) have been reported. The products of title reaction CH3CH2OCHCH3, CF3CHOCF2CHF2 and CF3CHOCH3 are further oxidized into organic nitrates in the presence of O2 and NO. Organic nitrites can be isomerized into organic nitrates or degraded to form CH3C(O•)HOCH2CH3, CF3C(O•)HOCF2CHF2 and CH3C(O•)HOCF3 alkoxy radicals and NO2. This work provides deep insight into the night migration and transformation mechanism of the three ethers.

6.
Phys Chem Chem Phys ; 21(31): 17378-17392, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31355843

RESUMO

The oxidation mechanisms and dynamics of 3-methoxy-3-methyl-1-butanol (3M3M1B) initiated by ˙OH radicals were assessed by the density functional theory and canonical variational transition state theory. The effects of ubiquitous water on the title reactions were analyzed by utilizing an implicit solvation model in the present system. The results suggested that aqueous water played a negative role in the ˙OH-initiated degradation of 3M3M1B with an increase in the Gibbs free barriers. Meanwhile, the barriers were almost independent when explicit water molecules were involved in the gaseous phase, which could reduce the rate constant by approximately 3 orders of magnitude. The kinetic calculations showed that the rate constants were smaller by about 15, 9, 8, and 8 orders of magnitude for hydroxyl-, ammonia-, formic acid-, and sulfur acid-participating reactions, respectively, than that from an unassisted reaction. The results indicated that water, hydroxyl, ammonia, formic acid, or sulfur acid could not facilitate the title reaction when performed in the atmosphere. The investigations of the subsequent oxidation processes of the alkyl radical CH3OC(CH3)2CH2C·HOH indicated that CH3OC(CH3)2CH2CHO was the most favorable product by eliminating an HO2˙ radical. Additionally, the HO2˙ radical could serve as a self-catalyst to affect the above reaction through a double proton transfer process. With the introduction of NO, CH3OC(CH3)2CH2COOH and HNO2 were found to be the main products, which may be regarded as the new source of atmospheric nitrous acid. In the NO2-rich environment, the peroxynitrate of CH3OC(CH3)2CH2CH(OONO2)OH could be formed via the reaction of the CH3OC(CH3)2CH2CH(OO˙)OH radical with NO2. The degradation mechanism of CH3OC(CH3)2CH2CH(OONO2)OH in the presence of water, ammonia, and methylamine was demonstrated, and it was shown that water, ammonia, and methylamine could promote the formation of nitric hydrate and nitrate aerosol. The main species detected in the experiment were confirmed by a theoretical study. The atmospheric lifetimes of 3M3M1B in the temperature range of 217-298 K and altitude of 0-12 km were within the range of 6.83-8.64 h. This study provides insights into the transformation of 3M3M1B in a complex environment.

7.
Chemphyschem ; 19(20): 2751-2757, 2018 10 19.
Artigo em Inglês | MEDLINE | ID: mdl-29992730

RESUMO

Increased interest has been devoted to the discovery of multifunctional materials with desirable properties, as continuous performance enhancement of various devices mainly depends on high-performance materials. Now, density functional theory has become a powerful tool to design new materials and rationalize experimental observations. In this work, we explored the photophysical properties origin of chiral boron heptaaryldipyrromethene (heptaaryl-BODIPY), which has charming optoelectronic properties. At the same time, we designed the other five compounds on the basis of heptaaryl-BODIPY. The simulated electronic absorption and emission spectra of heptaaryl-BODIPY are in agreement with experimental ones, allowing us to reliably assign its electronic transition property. The designed compound 6 shows remarkably large first hyperpolarizability value up to 82.78×10-30  esu. For this kind of compounds, their NLO response values associate with not only position but also electronic nature of substituent groups. Moreover, electron reorganization energies of compounds 1-4 are comparable to tris(8-hydroxyquinolinato)aluminium(III) which is a typical electron transport material. Intriguingly, the studied compounds are the excellent fluorescent probe materials from the standpoint of large Stokes shift and high emission efficiency. Our work enables an opportunity for understanding the relationship between microelectronic structure and macroscopic performance of BODIPY derivatives.

8.
Sci Rep ; 7: 40264, 2017 01 09.
Artigo em Inglês | MEDLINE | ID: mdl-28067283

RESUMO

In this study, the mechanistic and kinetic analysis for reactions of CF3OCH(CF3)2 and CF3OCF2CF2H with OH radicals and Cl atoms have been performed at the CCSD(T)//B3LYP/6-311++G(d,p) level. Kinetic isotope effects for reactions CF3OCH(CF3)2/CF3OCD(CF3)2 and CF3OCF2CF2H/CF3OCF2CF2D with OH and Cl were estimated so as to provide the theoretical estimation for future laboratory investigation. All rate constants, computed by canonical variational transition state theory (CVT) with the small-curvature tunneling correction (SCT), are in reasonable agreement with the limited experimental data. Standard enthalpies of formation for the species were also calculated. Atmospheric lifetime and global warming potentials (GWPs) of the reaction species were estimated, the large lifetimes and GWPs show that the environmental impact of them cannot be ignored. The organic nitrates can be produced by the further oxidation of CF3OC(•)(CF3)2 and CF3OCF2CF2• in the presence of O2 and NO. The subsequent decomposition pathways of CF3OC(O•)(CF3)2 and CF3OCF2CF2O• radicals were studied in detail. The derived Arrhenius expressions for the rate coefficients over 230-350 K are: k T(1) = 5.00 × 10-24T3.57 exp(-849.73/T), k T(2) = 1.79 × 10-24T4.84 exp(-4262.65/T), kT(3) = 1.94 × 10-24 T4.18 exp(-884.26/T), and k T(4) = 9.44 × 10-28T5.25 exp(-913.45/T) cm3 molecule-1 s-1.

9.
J Mol Graph Model ; 72: 156-167, 2017 03.
Artigo em Inglês | MEDLINE | ID: mdl-28092834

RESUMO

The NO3-initiated reactions of CH3OCH3 and CH3OCH2CH3 have been investigated by the BHandHLYP method in conjunction with the 6-311G(d,p) basis set. Thermodynamic and kinetic data are further refined using the comparatively accurate CCSD(T) method. According to the values of reaction enthalpies (ΔHr,298θ) and reaction Gibbs free energies (ΔGr,298θ) from CH3OCH2CH3 with NO3 system, we find that H-abstraction pathway from the α-CH2 group is more exothermic. It is further confirmed by the calculated CH bond dissociation energy of CH3OCH2CH3 molecule. All the rate constants, computed through means of canonical variational transition state with small-curvature tunneling correction, are fitted to the three-parameter expressions k1=1.54×10-23T3.34exp(-1035.53/T) and k2=3.55×10-26T4.31exp(-281.24/T)cm3molecule-1s-1 and branching ratios are computed over the temperature range 200-600K. The branching ratios are also discussed. The atmospheric lifetimes of CH3OCH3 and CH3OCH2CH3 determined by the NO3 radical are about 270 and 29days, respectively.


Assuntos
Atmosfera/química , Éteres/química , Modelos Moleculares , Nitratos/química , Elétrons , Cinética , Conformação Molecular , Estereoisomerismo , Termodinâmica , Vibração
10.
Chemosphere ; 171: 49-56, 2017 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-28002766

RESUMO

In this work, the density functional and high-level ab initio theories are adopted to investigate the mechanisms and kinetics of reaction of (CH3)3CC(O)X (X = F, Cl, and Br) with atomic chlorine. Rate coefficients for the reactions of chlorine atom with (CH3)3CC(O)F (k1), (CH3)3CC(O)Cl (k2), and (CH3)3CC(O)Br (k3) are calculated using canonical variational transition state theory coupled with small curvature tunneling method over a wide range of temperatures from 250 to 1000 K. The dynamic calculations are performed by the variational transition state theory with the interpolated single-point energies method at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311++G(d,p) level of theory. Computed rate constant is in good line with the available experimental value. The rate constants for the title reactions are in this order: k1

Assuntos
Cloro/química , Hidrocarbonetos Clorados/química , Óxido Nítrico/química , Oxigênio/química , Atmosfera , Aquecimento Global , Cinética , Oxirredução , Temperatura Ambiente
11.
J Phys Chem A ; 121(1): 226-237, 2017 Jan 12.
Artigo em Inglês | MEDLINE | ID: mdl-27958733

RESUMO

The effects on the hydrolysis of NO2 in the presence of methylamine and dimethylamine molecules were investigated by theoretical calculations of a series of the molecular clusters 2NO2-mH2O-CH3NH2 (m = 1-3) and 2NO2-mH2O-(CH3)2NH (m = 1, 2). With methylamine included in the clusters, the energy barrier is reduced by 3.2 kcal/mol from that with ammonia, and the corresponding products may form without an energy barrier. The results show that amines have larger effects than ammonia in promoting the hydrolysis of NO2 on thermodynamics. The additional water molecules can stabilize the transition states and the product complexes, and we infer that adding more water molecules in the reactions mainly act as solvent and promoting to form the methylamine nitrate (CH3NH3+NO3-). In addition, the interactions of CH3NH2 and (CH3)2NH on the hydration of HNO3 are also more effective than NH3, and the NH4NO3, CH3NH3NO3, and (CH3)2NH2NO3 complexes tend to form the larger aerosols with the increasing of water molecules. The equilibrium geometries, harmonic vibrational frequencies, and intensities of both HONO-CH3NH2 and HONO-NH3 complexes were investigated. Calculations predict that the binding energies of both HONO-CH3NH2 complexes are larger than HONO-NH3 complexes, and the OH stretching vibrational frequencies and intensities are most affected. The natural bond orbital analysis was performed to describe the donor-acceptor interactions on a series of complexes in the reactions 2NO2 + H2O + CH3NH2 and 2NO2 + H2O + (CH3)2NH, as well as the complexes of HONO-NH3 and HONO-CH3NH2. The results show that the interactions with amines are relatively larger, and the higher stabilization energies between CH3NH2 and HONO are found.

12.
Environ Sci Pollut Res Int ; 23(23): 23467-23484, 2016 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-27614635

RESUMO

Multichannel gas-phase reactions of CH3OCH2CH2Cl/CH3CH2OCH2CH2Cl with chlorine atom and hydroxyl radical have been investigated using ab initio method and canonical variational transition-state dynamic computations with the small-curvature tunneling correction. Further energetic information is refined by the coupled-cluster calculations with single and double excitations (CCSD)(T) method. Both hydrogen abstraction and displacement processes are carried out at the same level. Our results reveal that H-abstraction from the -OCH2- group is the dominant channel for CH3OCH2CH2Cl by OH radical or Cl atom, and from α-CH2 of the group CH3CH2- is predominate for the reaction CH3CH2OCH2CH2Cl with Cl/OH. The contribution of displacement processes may be unimportant due to the high barriers. The values of the calculated rate constants reproduce remarkably well the available experiment data. Standard enthalpies of formation for reactants and product radicals are calculated by isodesmic reactions. The Arrhenius expressions are given within 220-1200 K. The atmospheric lifetime, ozone depleting potential (ODP), ozone formation potential (OFP), and global warming potential (GWP) of CH3OCH2CH2Cl/CH3CH2OCH2CH2Cl are investigated. Meanwhile, the atmospheric fate of the alkoxy radicals are also researched using the same level of theory. To shed light on the atmospheric degradation, a mechanistic study is obtained, which indicates that reaction with O2 is the dominant path for the decomposition of CH3OCH(O•)CH2Cl, the C-C bond scission reaction is the primary reaction path in the consumption of CH3CH(O•)OCH2CH2Cl in the atmosphere. HIGHLIGHTS: Ab initio method and canonical variational transition-state theory are employed to study the kinetic nature of hydrogen abstraction reactions of CH3OCH2CH2Cl/CH3CH2OCH2CH2Cl with Cl atom and OH radical and fate of alkoxy radicals (CH3OCH(O•)CH2Cl/CH3CH(O•)OCH2CH2Cl).


Assuntos
Álcoois/química , Cloro/química , Hidrocarbonetos Clorados/química , Hidrogênio/química , Radical Hidroxila/química , Poluentes Atmosféricos/química , Poluição do Ar , Simulação por Computador , Hidrogênio/isolamento & purificação , Cinética , Modelos Químicos , Conformação Molecular , Termodinâmica
13.
Dalton Trans ; 45(17): 7285-93, 2016 05 07.
Artigo em Inglês | MEDLINE | ID: mdl-27009569

RESUMO

Chiral transition metal complexes not only have large nonlinear optical (NLO) response but also meet the non-centrosymmetric requirement of second-order NLO materials. Therefore, chiral transition metal complexes become very active in the NLO area. Recently, the second-order NLO response of chiral dinuclear Re(i) complex 2 has been found to be 1.5 times larger than that of KH2PO4 (KDP) based on experimental measurement. However, its NLO origin has not been determined and a structure-property relationship has not been established at the microscopic level, which are very important to further improve the performance. It is found that charge transfer from metal to ligand is mainly responsible for its NLO origin. Based on complex 2, the designed complexes have remarkably large second-order NLO activity. For instance, the designed complex 9 has a very large second-order NLO response value (115.81 × 10(-30) esu), which is about 668 times larger than the organic molecule urea. Moreover, time-dependent density functional theory (TDDFT) calculations have been used to investigate their UV-Vis/CD spectra. The simulated circular dichroism (CD) spectra of the complex 2 are in good agreement with the experimental ones, which can be used to assign the absolute configurations (ACs) of chiral dinuclear Re(i) complexes with high confidence. The electronic absorption wavelengths, electron transition properties, and the second-order NLO responses strongly depend on the nature of substituent, different ligands (pyridine and isoquinoline) and their combinations. Based on NBO analysis, the interactions between [Re(CO)3Cl] fragments and ligands are of n →σ* character.

14.
Chemphyschem ; 16(8): 1768-76, 2015 Jun 08.
Artigo em Inglês | MEDLINE | ID: mdl-25872761

RESUMO

The mechanism and kinetics of the reactions of CF(3)COOCH(2)CH(3), CF(2)HCOOCH(3), and CF(3)COOCH(3) with Cl and OH radicals are studied using the B3LYP, MP2, BHandHLYP, and M06-2X methods with the 6-311G(d,p) basis set. The study is further refined by using the CCSD(T) and QCISD(T)/6-311++G(d,p) methods. Seven hydrogen-abstraction channels are found. All the rate constants, computed by a dual-level direct method with a small-curvature tunneling correction, are in good agreement with the experimental data. The tunneling effect is found to be important for the calculated rate constants in the low-temperature range. For the reaction of CF(3)COOCH(2)CH(3) +Cl, H-abstraction from the CH(2) group is found to be the dominant reaction channel. The standard enthalpies of formation for the species are also calculated. The Arrhenius expressions are fitted within 200-1000 K as kT(1) =8.4×10(-20) T (2.63) exp(381.28/T), kT(2) =2.95×10(-21) T (3.13) exp(-103.21/T), kT(3) =1.25×10(-23) T (3.37) exp(791.98/T), and kT(4) =4.53×10(-22) T (3.07) exp(465.00/T).

15.
J Phys Chem A ; 119(8): 1256-66, 2015 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-25629584

RESUMO

Reactions of (CF3)2CFOCH3 and (CF3)2CFOCHO with hydroxyl radical and chlorine atom are studied at the B3LYP and BHandHLYP/6-311+G(d,p) levels along with the geometries and frequencies of all stationary points. This study is further refined by CCSD(T) and QCISD(T)/6-311+G(d,p) methods in the minimum energy paths. For the reaction (CF3)2CFOCH3 + OH, two hydrogen abstraction channels are found. The total rate constants for the reactions (CF3)2CFOCH3 + OH/Cl and (CF3)2CFOCHO + Cl are followed by means of the canonical variational transition state with the small-curvature tunneling correction. The comparison between the hydrogen abstraction rate constants by hydroxyl and chlorine atom is discussed. Calculated rate constants are in reasonable agreement with the available experiment data. The standard enthalpies of formation for the reactants, (CF3)2CFOCH3 and (CF3)2CFOCHO, and two products, (CF3)2CFOCH2 and (CF3)2CFOCO, are evaluated by a series of isodesmic reactions. The Arrhenius expressions for the title reactions are given as follows: k1= 1.08 × 10(-22) T(3.38) exp(-213.31/T), k2= 3.55 × 10(-22) T(3.61) exp(-240.26/T), and k3= 3.00 × 10 (-19) T(2.58) exp(-1294.34/T) cm(3) molecule(-1) s(-1).

16.
J Mol Model ; 20(9): 2419, 2014 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-25129661

RESUMO

The reaction of CHF2OCF2CHFCl with atomic chlorine was studied using B3LYP/6-311G(d,p), BHandHLYP/6-311G(d,p), and M06-2X/6-311G(d,p) methods and further using CCSD(T) and QCISD(T) methods. Two hydrogen abstraction channels were found for the title reaction. Dynamics calculations were followed by means of canonical variational transition state with the small-curvature tunneling correction between 220 and 2,000 K. Our rate constant k = 2.90 × 10(-15) cm(3) molecule(-1) s(-1) is in reasonable agreement with the available data (3.20 ± 0.32) × 10(-15) cm(3) molecule(-1) s(-1) at 296 K. The three-parameter Arrhenius expression (in the unit of cm(3) molecule(-1) s(-1)) for the title reaction is given as k (T) = 1.38 × 10 (-19) T (2.57) exp (-2622.95/T).

17.
Dalton Trans ; 43(25): 9655-60, 2014 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-24839638

RESUMO

Recently, a new sulfide cluster fullerene, Sc2S@Cs (10528)-C72 containing two pairs of fused pentagons has been isolated and characterized (Chen et al., J. Am. Chem. Soc., 2012, 134, 7851). Inspired by this investigation, we propose a question: what properties will be influenced by the interaction between the encapsulated V-shaped polar molecule and C72? To answer this question, four encapsulated metallic fullerenes (EMFs) M2N@C72 (M = Sc or Y, N = S or O) along with pristine Cs-C72 (10528) were investigated by quantum chemistry methods. The results show that the Egap (3.01-3.14 eV) of M2N@C72 are significantly greater than that of pristine Cs-C72 (10528) (2.34 eV). This indicates that the stabilities of these EMFs increase by encapsulating the V-shaped polar molecule into the fullerene. Furthermore, the natural bond orbital (NBO) charge analysis indicates electron transfer from M2N to C72 cage, which plays a crucial role in enhancing first hyperpolarizability (ßtot). The ßtot follows the order of 1174 au (Y2O@C72) ≈ 1179 au (Sc2O@C72) > 886 au (Y2S@C72) ≈ 864 au (Sc2S@C72) > 355 au (C72). This indicates that the ßtot of M2N@C72 is more remarkable than that of pristine Cs-C72 (10528) due to the induction effect of the encapsulated molecule. Compared with sulfide cluster fullerenes (Y2S@C72 and Sc2S@C72), oxide cluster fullerenes (Sc2O@C72 and Y2O@C72) show much larger ßtot due to the small ionic radius and the large electronegativity of oxygen. In contrast, the metal element (scandium and yttrium) has a slight influence on the ßtot. Thus, oxide cluster fullerenes are candidates to become promising nonlinear optical materials with higher performance.


Assuntos
Fulerenos/química , Compostos Organometálicos/química , Escândio/química , Ítrio/química , Modelos Moleculares , Estrutura Molecular , Fenômenos Ópticos , Oxigênio/química , Teoria Quântica , Sulfetos/química
18.
J Chem Phys ; 140(8): 084309, 2014 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-24588171

RESUMO

The reaction of allyl chloride with the hydroxyl radical has been investigated on a sound theoretical basis. This is the first time to gain a conclusive insight into the reaction mechanism and kinetics for important pathways in detail. The reaction mechanism confirms that OH addition to the C=C double bond forms the chemically activated adducts, IM1 (CH2CHOHCH2Cl) and IM2 (CH2OHCHCH2Cl) via low barriers, and direct H-abstraction paths may also occur. Variational transition state model and multichannel RRKM theory are employed to calculate the temperature-, pressure-dependent rate constants. The calculated rate constants are in good agreement with the experimental data. At 100 Torr with He as bath gas, IM6 formed by collisional stabilization is the major products in the temperature range 200-600 K; the production of CH2CHCHCl via hydrogen abstractions becomes dominant at high temperatures (600-3000 K).


Assuntos
Compostos Alílicos/química , Gases/química , Radical Hidroxila/química , Teoria Quântica , Pressão , Temperatura Ambiente
19.
J Mol Graph Model ; 48: 18-27, 2014 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-24366002

RESUMO

Potential energy surface for the reaction of hydroxyl radical (OH) with 3-fluoropropene (CH2CHCH2F) has been studied to evaluate the reaction mechanisms, possible products and rate constants. It has been shown that the CH2CHCH2F with OH reaction takes place via a barrierless addition/elimination and hydrogen abstraction mechanism. It is revealed for the first time that the initial step for the barrierless additional process involves a pre-reactive loosely bound complex (CR1) that is 1.60 kcal/mol below the energy of the reactants. Subsequently, the reaction bifurcates into two different pathways to form IM1 (CH2CHOHCH2F) and IM2 (CH2OHCHCH2F), which can decompose or isomerize to various products via complicated mechanisms. Variational transition state model and multichannel RRKM theory are employed to calculate the temperature-, pressure-dependent rate constants and branching ratios. At atmospheric pressure with He as bath gas, IM1 formed by collisional stabilization is dominated at T≤600 K; whereas the direct hydrogen abstraction leading to CH2CHCHF and H2O are the major products at temperatures between 600 and 3000 K, with estimated contribution of 72.9% at 1000 K. Furthermore, the predicted rate constants are in good agreement with the available experimental values.


Assuntos
Alcanos/química , Hidrocarbonetos Fluorados/química , Radical Hidroxila/química , Simulação por Computador , Cinética , Modelos Químicos , Modelos Moleculares , Termodinâmica
20.
J Phys Chem A ; 117(30): 6629-40, 2013 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-23865514

RESUMO

The complex potential energy surface of allyl alcohol (CH2CHCH2OH) with hydroxyl radical (OH) has been investigated at the G3(MP2)//MP2/6-311++G(d,p) level. On the surface, two kinds of pathways are revealed, namely, direct hydrogen abstraction and addition/elimination. Rice-Ramsperger-Kassel-Marcus theory and transition state theory are carried out to calculate the total and individual rate constants over a wide temperature and pressure region with tunneling correction. It is predicted that CH2CHOHCH2OH (IM1) formed by collisional stabilization is dominate in the temperature range (200-440 K) at atmospheric pressure with N2 (200-315 K at 10 Torr Ar and 100 Torr He). The production of CH2CHCHOH + H2O via direct hydrogen abstraction becomes dominate at higher temperature. The kinetic isotope effect (KIE) has also been calculated for the title reaction. Moreover, the calculated rate constants and KIE are in good agreement with the experimental data.


Assuntos
Gases/química , Hidrogênio/química , Radical Hidroxila/química , Modelos Químicos , Propanóis/química , Pressão Atmosférica , Simulação por Computador , Cinética , Temperatura Ambiente , Termodinâmica
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