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Theoretical Study on the Gas Phase Reaction of Allyl Bromide with Hydroxyl Radical
Computational and Theoretical Chemistry 1102 (2017) 114–126
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Theoretical Study on the Gas Phase Reaction of Allyl Bromide with Hydroxyl Radical Yunju Zhang a,⇑, Yuxi Sun a, Jingyu Sun b, Rongshun Wang c a
Key Laboratory of Photoinduced Functional Materials, Mianyang Normal University, Mianyang 621000, PR China Hubei Collaborative Innovation Center for Rare Metal Chemistry, Hubei Key Laboratory of Pollutant Analysis & Reuse Technology, College of Chemistry and Chemical Engineering, Hubei Normal University, Cihu Road 11, Huangshi, Hubei 435002, PR China c Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Renmin Road 5268, Changchun, Jilin 130024, PR China b
a r t i c l e
i n f o
Article history: Received 13 November 2016 Received in revised form 31 December 2016 Accepted 5 January 2017 Available online 6 January 2017 Keywords: OH Allyl bromide Reaction mechanism Rate constants Photolysis
a b s t r a c t Mechanisms and reaction channels of the allyl bromide (CH2@CHCH2Br) with OH reaction are studied using quantum chemistry. It is predicted that the H(or Br)-abstraction and addition/elimination mechanisms have been revealed on potential energy surface (PES). Direct H-abstract from the ACH2Br group of CH2@CHCH2Br leading to h-P1 (CH2CHCHBr + H2O) is dominant. As for addition/elimination mechanism, it is shown that the reaction is initiated by the addition of OH radical to the C@C bond of CH2@CHCH2Br to barrierlessly generate the intermediates IM1 and IM2, respectively. Multichannel RRKM theory and variational transition-state theory (VTST) are employed to evaluate the rate constants of temperature- and pressure-dependent. The calculated rate constants are in good agreement with the available experimental data. At 100 Torr with helium as bath gas, IM3 (CH2OHCHBrCH2) formed by collisional stabilization and the final products P1 (CH2OH + CH2CHBr) are the major product in the temperature range of 200– 700 K and 700–1000 K, respectively. The production of CH2@CHCHBr via hydrogen abstraction becomes dominant at high temperatures (T P 1000 K). Time-dependent DFT (TD-DFT) calculations indicate that IM1-IM4, IM6, IM8 and IM9 take photolysis easily in the sunlight at the wavelength of 333 nm, 244 nm, 327 nm, 313 nm, 298 nm, 305 nm and 428 nm, once they are generated. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Halogenated organic contaminants (HOCs) mainly include the fluorinated organic compounds (FOCs), chlorinated organic compounds (COCs) and brominated organic compounds (BOCs), which show the characteristics of persistent organic pollutants in environment. Chlorinated organic compounds and brominated organic compounds contain either chlorine or bromine atoms, and thus have ozone depletion potential (ODP) [1]. Because bromine atoms and brominated organic compounds are estimated to be 40–50 times more effective than chlorine atoms and chlorinated organic compounds in ozone destruction, brominated organic compounds are particularly problematic in processes related to climate changes and play a significant role in the depletion of the stratospheric ozone [2]. Allyl bromide is widely used in industrial and agricultural production as raw materials, solvents and so on, and it can be released into environment through a variety of wastewater streams. In addition to their environmental effects, a number of studies have reported that health effects have also been identified. ⇑ Corresponding author. http://dx.doi.org/10.1016/j.comptc.2017.01.005 2210-271X/Ó 2017 Elsevier B.V. All rights reserved.
For example, allyl bromide could irritate eyes, skin and respiratory system. Experimentally, the reactions involving allyl bromide (CH2@CHCH2Br) with many radicals and molecules have been investigated extensively, including reactions such as CH2@CHCH2Br with OH, Cl, NO3, O3 [3–6], respectively, which indicating that the dominant atmospheric loss pathway for allyl bromide may be reaction with OH radical. Up to date, only one experimental kinetic study have been reported the reaction of OH with CH2@CHCH2Br. In 2003, Albaladejo and Ballesteros [3] measured the rate constant to be of the reaction OH þ CH2 @CHCH2 Br ! products (3.6 ± 1.5) 1012 exp(3783 ± 964/RT) cm3 molecules1 s1 at P = 100 Torr and in the temperature range 228–388 K using the pulsed laser photolysis/laser-induced fluorescence technique. However, the detailed mechanisms of the degradation products of allyl bromide in atmosphere are unclear for the title reaction. Therefore, in order to detailed understand mechanistic and kinetic of the OH + CH2@CHCH2Br reaction and understand the chemical reactivity of CH2@CHCH2Br with OH in the atmospheric conditions, it is necessary to present the mechanistic and kinetic studies for the reaction of OH with CH2@CHCH2Br in this work.
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2. Computational methods Electronic structure calculations are performed with Gaussian 09 program package [7]. The optimized geometries and harmonic frequencies of all the stationary points are obtained at the M06-2X [8,9]/6-311++G(d,p) level. The nature of all stationary structure is verified by harmonic vibrational frequency calculations, namely, equilibrium species possess all real frequencies; transition states (TS) possess only one imaginary frequency. The zero-point energy (ZPE) corrections are obtained at the same level. The transition states were subjected to intrinsic reaction coordinate (IRC) [10,11] calculations to confirm connection with designated intermediates. To prove the energy prediction, the CCSD(T) [12] method with the cc-pVTZ basis set was used to calculate the single point energies based on the M06-2X/6-311++G(d,p) optimized geometries. We choose the important product channels to calculate the rate constants using the variational transition-state theory (VTST) and multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) theory [13]. In the section of the kinetic calculations, we employed the modified computer program written by Hou and Wang for the OH with allyl bromide reaction [14], and this methodology has been successfully used to deal with the complex reactions [15–19]. 3. Results and discussion The optimized structures of stationary points (the complex, intermediates, transition states, reactant and products) are listed in Figs. 1–3, along with the available experimental values, respectively. As seen in Fig. 3, the calculated bond lengths and angles at the M06-2X/6-311++G(d,p) level are in good agreement with experimental data [20], indicating that the M06-2X/6-311++G(d, p) method is suitable for predicting the geometry of the title reaction. To clarify the reaction mechanism, the potential energy surface (PES) for this reaction at CCSD(T)/cc-pVTZ//M06-2X/6-311++ G(d,p) is described in Fig. 4. The ZPE, relative energies, reaction enthalpies and Gibbs free energy for all the stationary points are listed in Table 1. Table S1 displays the harmonic vibrational frequencies and the moment of inertia (au) of all species, respectively. The frequencies of CH2CHOH, CH2CHBr, CH3CHO, CH2OH, CH2O, CH3, H2O, HOBr and OH are in agreement with experimental data [20]. Unless mentioned otherwise, the geometric parameters used in the discussion are the M06-2X/6-311++G(d,p) results, and the energies used are at the CCSD(T)/cc-pVTZ + ZPE level. 3.1. Reaction mechanism As the OH radical can have either abstraction or addition/elimination mechanism, two distinguishable type initial attacks have been revealed for the radical–molecule reaction OH + CH2@CHCH2Br, namely, the attack on H (or Br) atom and the addition to the C@C double bond (addition–isomerization–elimination). A detailed discussion on the title reaction mechanisms is given as follows. 3.1.1. Initial association The OH-allyl bromide surface is characterized by two bound intermediates, denoted as IM1 and IM2. The initial step involves the addition of the OH radical to the C atom of the C@C bond of CH2@CHCH2Br, generating the relatively stable radicals IM1 (CH2OHCHCH2Br) and IM2 (CH2CHOHCH2Br), respectively. The reaction coordinate is complicated by an initial energy minimum at CR1, which is a weakly bound complex with a 2.38 kcal/mol barrier to further rearrangement. This typical phenomenon is also proposed by Singleton and Cvetanovic et al [21]. Therefore, the reaction of OH with allyl bromide to form IM1 and IM2 is effectively without barrier. After formed the CR1, the oxygen atom of the
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OH radical should rotate and add to the carbon atom of C@C double bond in CH2@CHCH2Br via TS1 and TS2 to form IM1 and IM2, and the corresponding barrier heights are calculated to be 3.07 and 1.31 kcal/mol, respectively. The relative energy of TS1 is 1.76 kcal/mol higher than that of TS2, Moreover, the DG (298 K) data for the OH addition to the central-carbon atom (TS2) is 1.22 kcal/mol lower than that addition to the terminal-carbon atom (TS1) of the C@C double bond. These results indicate that the center Caddition is slightly preferred over the terminal C-addition addition. As seen in Fig. 4 and Table 1, the formation of IM1 and IM2 are thermodynamically favorable. In the following part, we will focus on discussing the formation pathways of various products which associated with IM1 and IM2, respectively. 3.1.2. The unimolecular reaction of IM1 3.1.2.1. The CH2OH radical formation channel. Clearly, from IM1 (29.32), there are two feasible pathways to form P1 (CH2OH + CH2CHBr). They can be written as follows
PathP1ð1ÞR ! CR1 ! IM1 ! IM3 ! P1ðCH2 OH þ CH2 CHBrÞ PathP1ð2ÞR ! CR1 ! I M1 ! IM4 ! P1ðCH2 OH þ CH2 CHBrÞ IM1 can undergo a 1,2-Br shift to form IM3 (CH2OHCHBrCH2) via transition state TS3 as shown in Path P1(1), or 1,2-H shift to form IM4 (CH2OHCH2CHBr) via transition state TS4 as shown in Path P1(2), respectively. Finally, both IM3 and IM4 can dissociate to P1 via CAC bond rupture corresponding transition state TS5 and TS6, respectively. For IM1 ? P1 conversion, two barriers must be surmounted in Path P1(1), which are 1.60 and 32.53 kcal/mol for the steps of IM1 ? IM3 and IM3 ? P1, respectively, it should be noted that the barrier of IM1 ? IM3 is the lowest barrier among all the subsequent reaction channels of IM1 and IM2; while in Path P1 (2), the barriers are 43.64 (IM1 ? IM4) and 28.13 (IM4 ? P1) kcal/mol, respectively. Due to the higher isomerization barrier, we expect that Path P1(2) should be less competitive with Path P1(1). 3.1.2.2. The CH2O radical formation channel. The hydrogen atom of the OH group in IM1 is migrating to the C-central atom via TS7 to form another intermediate IM5 (CH2OCH2CH2Br). The barrier height for IM1 ? IM5 is about 33.76 kcal/mol, which is 9.88 kcal/mol lower than TS4, and 32.16 kcal/mol higher than TS3. Subsequently, IM5 decomposes to form the final products P2 (CH2O + CH2CH2Br) via transition state TS8. The formation pathway of P2 can be written as
PathP2R ! CR1 ! IM1 ! IM5 ! P2ðCH2 O þ CH2 CH2 BrÞ The barrier height for this step is 17.12 kcal/mol. However, TS8 is still lower than the reactants by 6.04 kcal/mol and TS1 by 6.73 kcal/mol, which indicating that P2 is easily yielded once IM5 is formed by increasing temperatures. 3.1.2.3. The CH2Br radical formation channel from IM1. Starting from IM1, only one feasible channel is associated with the formation of CH2Br radical, which can be written as
PathP3ð1ÞR ! CR1 ! IM1 ! IM6 ! P3ðCH2 Br þ CH2CHOHÞ IM1 can isomerize to IM6 (CHOHCH2CH2Br) via a triangular structure transition state TS9. The barrier height of TS9 is 39.10 kcal/mol with respect to IM1, which is 5.34 kcal/mol higher than TS7 and 37.50 kcal/mol higher than TS3, as well as higher than TS1 9.09 kcal/mol. IM6, -30.36 kcal/mol relative to the initial reactants, breaks the CAC bond to give rise to P3 (CH2Br + CH2CHOH) via TS10 surmounting a 29.12 kcal/mol barrier height. Evidently, the ratedetermining step for the formation of P3 in Path P3(1) is the Hshift step, i.e., IM1 ? TS9 ? IM6, because the barriers for the entrance and decomposition steps TS1 and TS10 are both lower
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Fig. 1. Optimized geometries of species which connected to IM1 for the reaction of the CH2@CHCH2Br + OH reaction at M06-2X/6-311++(d,p) level.
than TS9. Moreover, due to higher isomerization barriers, this pathway should not play an important role at low and moderate temperatures, as confirmed by the kinetic calculation.
3.1.2.4. The H-atom formation channel from IM1. There are three feasible H-atom formation pathways from IM1, which can be depicted as
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Fig. 2. Optimized geometries of species which connected to IM1 for the reaction of the CH2@CHCH2Br + OH reaction at M06-2X/6–311++(d,p) level.
PathP4R ! CR1 ! IM1 ! P4ðH þ CHOHCHCH2 BrÞ
PathP5ð2ÞR ! CR1 ! IM1 ! IM6 ! P5ðH þ CH2 BrCH2 CHOÞ
PathP5ð1ÞR ! CR1 ! IM1 ! IM5 ! P5ðH þ CH2 BrCH2 CHOÞ
The IM1 ? IM5 and IM1 ? IM6 in Path P5(1) and Path P5(2) are two hydrogen migration processes, which are the same as that in
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Fig. 3. Optimized geometries of reactants and products for the reaction of the CH2@CHCH2Br + OH reaction at M06-2X/6-311++(d,p) level. Bond distances are in angstroms, and angles are in degrees. The values in italics are experimental data from ref 20.
Path P2 and Path P3(1), respectively. IM1, IM5 and IM6 can eliminate H atom to form two different products P4 (H + CHOHCHCH2Br) and P5 (H + CHOCH2CH2Br) via TS11, TS12 and TS13 via surmounting 35.66, 23.27 and 35.68 kcal/mol energy barriers, respectively. The relative energy of TS11 is 1.90 kcal/mol higher than that of the rate-determining transition state TS7 in Path P5(1), and is 3.44 kcal/mol lower than that of the rate-determining transition state TS9 in Path P5(2), respectively. Therefore, in view of the relative energies of rate-determining transition states and the simplicity, the pathway of Path P5(2) cannot compete with Path P4 and Path P5(1). 3.1.3. The unimolecular reaction of IM2 3.1.3.1. The CH2Br radical formation channel. For the CH2Br radical formation channels, two reaction scenarios are possible from IM2
Path P3ð2Þ R ! CR1 ! IM2 ! P3 ðCH2 Br þ CH2 CHOHÞ Path P6 R ! CR1 ! IM2 ! IM7 ! P6ðCH2 Br þ CH3 CHOÞ One is the direct decomposition of IM2 to the final products P3 via transition state TS14. This CAC bond fission barrier is quite low, i.e., 28.88 kcal/mol, which is the lowest barriers on the PES from IM2. Therefore, this formation of P3 channel should be the dominant pathway of IM2. The other minor reaction channel of IM2 involves the formation of another local minimum IM7 (CH3CHOCH2Br) via a 1,3-H shift transition state TS15. The barrier for this isomerization channel is 32.46 kcal/mol, which is 3.58 kcal/mol higher than that of TS14. After IM7 is formed, the CAC bond can dissociate to P6 (CH2Br + CH3CHO) involved transition state TS16. This cleavage process needs to surmount 15.56 kcal/mol barrier. TS16 is about
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Fig. 4. The profile of PES for the CH2@CHCH2Br + OH reaction at the CCSD(T)/cc-pVTZ//M06-2X/6-311++G(d,p) level, (a) terminal-C addition (b) central-C addition (c) abstraction, respectively.
8.98 kcal/mol lower than the reactants and 12.62 kcal/mol lower than TS15, therefore, once IM7 is generated, P6 is easily yielded by increasing temperatures. However, the rather higher isomer-
ization barrier of IM2 ? TS15 ? IM7 makes the pathway Path P6 far from competitive with pathway Path P3(2) under normal conditions.
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Table 1 Relative Energies(DE), Reaction Enthalpies(DH) and Gibbs Free Energy(DG) at 298 K for all the species in the CH2@CHCH2Br + OH reaction (energies in kcal/mol).
a b
Species
ZPE
DE a
DEb
DH0298 b
DG b
R:(CH2@CHCH2Br + OH) P1:(CH2OH + CH2CHBr) P2:(CH2O + CH2CH2Br) P3:(CH2Br + CH2CHOH) P4:(H + CHOHCHCH2Br) P5:(H + CHOCH2CH2Br) P6:(CH2Br + CH3CHO) P7:(CH3 + CH2BrCHO) P8:(CH3 + CHOHCHBr) P9:(H + CH2COHCH2Br) P10:(H + CH3COCH2Br) P11:(H + CH3COHCHBr) h-P1:(CH2CHCHBr + H2O) h-P2:(CH2CCH2Br + H2O) h-P3:(CHCHCH2Br + H2O) Br-P1:(CH2CHCH2 + HOBr) CR1 IM1 IM2 IM3 IM4 IM5 IM6 IM7 IM8 IM9 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 TS9 TS10 TS11 TS12 TS13 TS14 TS15 TS16 TS17 TS18 TS19 TS20 TS21 TS22 TS23 TS24 h-TS1 h-TS2 h-TS3 Br-TS1
0.00 50.21 49.79 50.08 48.41 47.89 49.35 48.40 49.00 47.98 47.51 47.57 49.67 49.47 49.79 49.76 51.69 54.55 53.61 54.32 54.33 54.26 54.53 53.36 53.86 54.01 51.76 51.94 54.23 51.16 51.60 51.93 51.68 51.94 51.33 51.82 49.34 49.16 48.87 51.53 51.16 51.78 51.38 50.80 51.13 48.98 48.80 50.92 48.44 49.09 48.74 48.63 48.26 51.12
0.00 6.82 15.04 10.36 1.86 8.07 20.06 15.66 11.82 2.91 13.48 6.96 32.28 12.86 6.18 7.13 4.77 33.50 32.50 34.73 30.86 26.59 34.22 27.69 33.63 45.79 0.76 2.54 32.74 10.04 1.14 3.14 2.18 8.70 1.72 3.97 3.35 3.15 1.88 2.61 1.78 11.03 9.44 8.88 2.52 4.54 5.49 1.54 3.27 0.08 0.12 2.58 4.68 12.68
0.00 5.67 13.92 9.45 1.21 6.70 20.14 15.99 11.06 0.61 11.68 4.76 31.42 10.28 4.12 7.36 2.38 29.32 28.82 30.52 27.97 23.16 30.36 24.54 30.91 40.10 0.69 1.07 27.72 14.32 2.01 0.16 4.44 6.04 9.78 1.24 6.34 0.11 5.32 0.06 3.64 8.98 7.24 11.78 0.58 6.62 3.10 6.82 0.78 2.10 0.69 3.58 5.98 11.75
0.00 5.78 13.95 9.54 1.20 6.67 20.02 15.69 10.88 0.62 11.48 4.58 31.22 9.82 3.79 5.60 2.64 30.35 29.87 31.66 28.96 24.52 31.55 25.49 31.90 40.82 0.08 2.03 29.09 13.34 1.13 0.71 2.96 7.17 8.55 2.04 5.31 1.09 4.30 0.80 2.10 9.98 8.23 10.42 1.39 5.52 4.14 5.70 1.63 1.02 0.09 2.90 5.36 11.15
0.00 8.04 15.90 11.92 4.06 4.06 22.98 16.70 11.48 2.34 9.26 1.92 32.02 11.28 4.98 11.14 5.21 20.93 19.87 21.40 19.42 14.41 21.49 16.26 22.12 31.88 8.69 7.47 18.66 22.86 10.52 8.34 13.35 2.52 18.46 6.60 15.14 8.90 13.89 8.50 12.93 0.62 1.36 20.87 8.02 15.60 5.54 15.70 7.59 11.16 8.28 11.44 13.81 19.93
M06-2X/6-311++G(d,p) level. CCSD(T)/cc-pVTZ//M06-2X/6-311++G(d,p) level.
3.1.3.2. The CH3 radical formation channel. For the CH3 radical formation channels, two pathways are energetically possible, which can be depicted as:
Path P7 R ! CR1 ! IM2 ! IM7 ! P7ðCH3 þ CH2 BrCHOÞ Path P8 R ! CR1 ! IM2 ! IM8 ! P8ðCH3 þ CHOHCHBrÞ The formation of IM7 is the same as that in Path P6. Subsequently, IM7 can further decompose to form P7 (CH3 + CH2BrCHO) via TS17, as in Path P7. The barrier for the step of IM7 ? P7 conversion is 17.30 kcal/mol. This bond cleavage path is exothermic by 15.69 kcal/mol. Compared with the formation of P6, P7 are less
stable than P6. Furthermore, the barrier height of TS17 is 1.74 kcal/mol higher than of TS16. Therefore, the formation of P6 channel occurs more preferentially than the formation of P7 channel. In Path P8, IM2 can transform to IM8 (CH3CHOHCHBr) via a four-membered-ring transition state TS18. The barrier height is 40.60 kcal/mol, which is higher than TS14 by 11.72 kcal/mol and TS15 by 8.14 kcal/mol, respectively. IM8, 30.91 kcal/mol relative to the initial reactants, can break the CAC bond to give rise to P8 (CH3 + CHOHCHBr) via TS19. The barrier height is 30.33 kcal/mol, which is 13.03 kcal/mol higher than that of the IM7 ? P7 conversion. These results indicate that the Path P8 occurs less favorable than the Path P7.
Y. Zhang et al. / Computational and Theoretical Chemistry 1102 (2017) 114–126
3.1.3.3. The H-atom formation channel. There are four H-atom formation pathways through IM2 which can transform to the corresponding product.
Path P9R ! CR1 ! IM2 ! P9 ðH þ CH2 COHCH2 BrÞ Path P10ð1Þ R ! CR1 ! IM2 ! IM7 ! P10ðH þ CH3 COCH2 BrÞ Path P10ð2Þ R ! CR1 ! IM2 ! IM9 ! P10ðH þ CH3 COCH2 BrÞ Path P11 R ! CR1 ! IM2 ! IM8 ! P11ðH þ CH3 COHCHBrÞ For the above four H-elimination pathways, which have the same steps of R ? CR1 ? IM2, and subsequently, isomer IM2 transforms to three different of products via four different reaction pathways. (i) In Path P9, IM2 can take CAH bond rupture leading to P9 (H + CH2COHCH2Br) via TS20. The dissociation barrier is 35.44 kcal/mol. (ii) The formation pathways of IM7 have been discussed in previous sections (in Path P6). For brevity, we decide not to discuss them again. IM7 can dissociate to P10 (H + CH3COCH2Br) via the CAH bond rupture transition state TS21 as in Path P10(1). The relative energy of rate-determining transition states TS15 in Path P10(1) is 2.98 kcal/mol lower than that of TS20 in Path P9, while 3.58 kcal/-
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mol higher than that of TS14 in Path P3(2). Therefore, in view of the relative energies of rate-determining transition states and the simplicity, we can conclude that Path P9 is less competitive than pathways Path P3(2) and P10(1), and Path P3(2) has priority over the pathway Path P10(1). (iii) In Path P10(2), a successive 1,2-H-shift and dissociation steps (IM2 ? IM9 ? P10) can also lead to product P10 (H + CH3COCH2Br) via transition states TS22 and TS23. It is an H-shift-H-elimination mechanism. Two high barriers need to be surmounted from IM2 to P10, that is, 35.64 and 39.32 kcal/mol for IM2 ? IM9 and IM9 ? P10 conversion, respectively. Because the rate-determining energy barrier (39.32) of Path P10(2) is higher than of Path P10(1) (32.46). Therefore, pathway Path P10(2) should be less competitive than pathway Path P10(1). (iv) For Path P11, the formation of IM8 is the same as that in Path P8. Subsequently, IM8 undergoes a H-elimination process to produce P11 (H + CH3COHCHBr) via TS24. The barrier for IM8 ? P11 conversion is 33.01 kcal/mol. Yet, the rate-determining energy barrier for Path P11 is 40.60 kcal/mol, which is 5.16, 8.14 and 1.28 kcal/mol higher than that of Path P9, Path P10(1) and Path P10(2), respectively. Therefore, from the kinetic consideration, for the above mentioned four H-elimination pathways, the order of reaction competition abilities is Path P10(1) > Path P9 > Path P10(2) > Path P11.
Fig. 5. Brief description of the progression on PES for the CH2@CHCH2Br + OH reaction.
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3.2. H-abstraction and Br-abstraction pathways As shown in Fig. 5, there are four different direct H (or Br) abstract pathways. The most favorable channel is the forming of h-P1 (CH2CHCHBr + H2O) via h-TS1. The energy of h-TS1 is only 0.69 kcal/mol higher than the reactants. The second and three channels corresponds to hydrogen abstraction channel by OH from the center C atom of -CH and -CH2 groups of CH2@CHCH2Br, leading to h-P2 (CH2CCH2Br + H2O) and h-P3 (CHCHCH2Br + H2O) via transition states h-TS2 and h-TS3 with the barrier height of 3.58 and 5.98 kcal/mol which is 2.89 and 5.29 slightly higher than that of h-TS1. The last pathway is abstracting the Br atom of CH2@CHCH2Br by OH radical to form the final product Br-P1 (HOBr + CH2CHCH2) via transition state Br-TS1. The calculated barrier height for this process is 11.75 kcal/mol, which are 11.06, 8.17 and 5.77 kcal/mol higher than h-TS1, h-TS2 and h-TS3, respectively. Moreover, the Gibbs energies (DG) of h-P2, h-P3 and Br-P1 are 20.74, 27.04 and 43.16 kcal/mol higher than that of h-P1, respectively. Obviously, the most feasible abstract channel is the formation of h-P1 among these four abstract pathways.
Scheme 2.
Scheme 3.
kP2 ðT; PÞ ¼
3.3. Kinetic calculation The kinetic calculation for the important reaction routes of the OH + CH2@CHCH2Br reaction (Schemes 1–3) is calculated by using the variational transition-state theory (VTST) and multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) theory on the basis of energetics, frequencies and moments of inertia of various relevant species. The reaction paths including in Schemes 1–3 are considered in the following calculation: where ‘‘⁄” represents the vibrational excitation of the intermediate (IMj). Steady-state assumption for energized intermediate (IMj⁄) leads to the following expressions (the detailed calculation processes are given in the Supporting information (Note S1)): For Scheme 1:
kIM1 ðT; PÞ ¼
kIM3 ðT; PÞ ¼
kIM5 ðT; PÞ ¼
kP1 ðT; PÞ ¼
aa
– Q– t Qr
– Q– t Qr
aa
aa
– Q– t Qr
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – k6 ðEÞ – Na ðE– ÞeE =RT dE X4 0
ð6Þ
X 3 ¼ k4 ðEÞ=ðk5 ðEÞ þ k8 ðEÞ þ xÞ X 4 ¼ X 1 k3 ðEÞ X 2 k5 ðEÞ X 3 For Scheme 2:
ð1Þ
kIM2 ðT; PÞ ¼
ð2Þ
kP3 ðT; PÞ ¼
ð3Þ
kP9 ðT; PÞ ¼
– Q– t Qr
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – k7 ðEÞX 2 – Na ðE– ÞeE =RT dE X 4 0
aa
ð5Þ
X 2 ¼ k2 ðEÞ=ðk3 ðEÞ þ k7 ðEÞ þ xÞ
– Q– t Qr
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – X3x – Na ðE– ÞeE =RT dE X 4 0
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – k8 ðEÞX 3 – N a ðE– ÞeE =RT dE X 4 0
With the following definition:
eEa =RT
h Q CH2 @CHCH2 Br Q OH Z 1 – X2x – Na ðE– ÞeE =RT dE X4 0
– Q– t Qr
X 1 ¼ k1 ðEÞ þ k2 ðEÞ þ k4 ðEÞ þ k6 ðEÞ þ x
eEa =RT
h Q CH2 @CHCH2 Br Q OH Z 1 – x – N a ðE– ÞeE =RT dE X4 0
aa
kP4 ðT; PÞ ¼
aa
aa
– Q– t Qr
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – x – Na ðE– ÞeE =RT dE X1 0
aa
– Q– t Qr
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – k2 ðEÞ – Na ðE– ÞeE =RT dE X1 0
aa
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – k3 ðEÞ – Na ðE– ÞeE =RT dE X 1 0
X 1 ¼ k1 ðEÞ þ k2 ðEÞ þ k3 ðEÞ þ x
Scheme 1.
ð8Þ
– Q– t Qr
With the following definition:
ð4Þ
ð7Þ
ð9Þ
Y. Zhang et al. / Computational and Theoretical Chemistry 1102 (2017) 114–126
The microcanonical rate constant is calculated using the RRKM theory as follows:
ki ðEÞ ¼ ai C i N i ðE– i Þ=hqj ðEj Þ
ð7Þ
In the above equations, aa is the statistical factor for the reaction path a, and ai is the statistical factor (degeneracy) for the ith reaction path; Ea is the energy barrier for the reaction step a. Q OH and Q CH2 @CHCH2 Br are the total partition function of OH and CH2– @CHCH2Br, respectively; Q – t and Q r are the translational and rotational partition functions of entrance transition state, respectively; N a ðE– Þ is the number of state for the association transition state with excess energy E– above the association barrier. ki ðEÞ is the energy-specific rate constant for the ith channel and Ci is the ratio of the overall rotational partition function of the TSi and IMj; N i ðE– i Þ is the number of states at the energy above the barrier height for transition state i; qj ðEj Þ is the density of states at energy Ej of the intermediate. The density of states and the number of states are
123
calculated using the extended Beyer-Swinehart algorithm [22,23]. Where x = bcZLJ[M] and bc is the collision efficiency, which is calculated using Troe’s weak collision approximation [22] with the energy transfer parameter hDEi, The simple expression for collisional energy transfer (hDEi) [24,25] is
bc 1 bc1=2
ffi
hDEi F E kT
This expression holds nearly exactly at the weak collision limit hDEi FEkT for all collision models [24,25]. The factor FE is set to 1.0 empirically. The average energy transfer per collision, i.e., hDEi, is unknown and cannot be calculated quantitatively. In consideration of the experimental rate constants, it is found that the values around 100 cm1 for hDEi should be reasonable to calculate the rate constants. ZLJ is the Lennard-Jones collision frequency. The collision efficiency is estimated using the Lennard-Jones potential (V(r) = 4e[(r/r)12 (r/r)6]) by fitting the interaction energies calculated at the M06-2X/6-311++G(d,p) level for IM1. . .He and
Fig. 6. Arrhenius plots of the total and individual rate constants for the CH2@CHCH2Br + OH reaction at 100 Torr He.
Fig. 7. Branching ratios for the CH2@CHCH2Br + OH reaction, which correspond to Fig. 3 with a pressure of 100 Torr He.
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Y. Zhang et al. / Computational and Theoretical Chemistry 1102 (2017) 114–126
IM2. . .He. It is estimated that (e = 42.38 K, r = 2.82 Å) for IM1. . .He and (e = 27.81 K, r = 2.86 Å) for IM2. . .He, and [M] is the concentration of the bath gas M (He). The weak collision approximation is used for the intermediate. The rate coefficients for the direct hydrogen abstraction routes can be readily obtained using the conventional transition-state theory, viz.:
kabs ðTÞ ¼ j1
kB T Q– TS eE1 =ðRTÞ h Q CH2 @CHCH2 Br Q OH
where j1 is the tunneling factor, kB and h are Boltzmann and Planck constants, respectively. Q – TS , Q CH2 @CHCH2 Br and Q OH are the h-TS1 (hTS2 or h-TS3), CH2@CHCH2Br and OH partition functions, respectively. E1 is the energy barrier of h-TS1 (h-TS2 or h-TS3). The unsymmetrical Eckart potential model is employed to estimate j1 [26,27]. The rate coefficients are calculated as a function of temperature in the range of 200–3000 K. Arrhenius plots of the total and individual rate constants at the whole temperature range and at the pressure of 100 Torr, He are shown in Fig. 6, together with some of the available experimental data for comparison between our computed and the available experimental data. The calculated results reveal that our calculated total rate constants at 228– 388 K are in good agreement with the available experimental val-
ues. The product branching ratios for the title reaction are shown in Fig. 7. As can be seen from Fig. 7, the fraction of the IM3 depends strongly on temperature. i.e., from 96.7 at 200 K, 37.1% at 700 K, and decreasing to 2.28% at 1200 K. Temperature-dependence of the fraction of the H-abstract (from CH2Br group) and P1 (CH2OH + CH2CHBr) are more complicated. For H-abstract, first, it sharply rises with temperature and reaches a maximum of 66.3% at about T = 2200 K, and then almost linearly decreases when temperature increase further. Similar changes occur for P1, the fraction of P1 sharply rises with increasing temperatures first at 200–900 K, from 0 at 200 K up to maximal point of 44.9% at 900 K, but drops at T P 1000 K, from 44.1% at 1000 K down to 1.45% at 3000 K. From Fig. 7, we can see that P1 is dominant products at 700–1000 K; h-P1 and IM3 are the major products at T P 1000 K and 200– 700 K, respectively. Meanwhile, we have also provided the rate constants in the temperature range of 200–3000 K at atmospheric pressure P = 760 Torr as presented in Fig. S1, At T = 298 K and P = 760 Torr, the total rate constant is 1.77 1011 cm3 molecule1 s1. For practical use, the predicted total and important individual rate constants are fitted to a modified three parameter Arrhenius expression. The rate constants for the total (ktot) and the formations of kIM1, kIM2, kIM3, kh-TS1 and kP1 in units of cm3 molecule1 s1 are presented, respectively, as follows:
K tot ¼ 5:46 1014 T 3:27 expð6:08=TÞð200 6 T 6 500Þ K tot ¼ 8:79 1012 T 0:99 expð0:76=TÞð500 < T 6 3000Þ K IM1 ¼ 4:53 1017 T 3:76 expð2:14=TÞð200 6 T 6 3000Þ K IM2 ¼ 1:58 106 T 2:58 expð119:95=TÞð200 6 T 6 500Þ K IM2 ¼ 5:62 1012 T 1:36 expð2569:62=TÞð500 6 T 6 3000Þ K IM3 ¼ 3:15 109 T 1:02 expð171:32=TÞð200 6 T 6 3000Þ K hTS1 ¼ 2:14 1014 T 1:25 expð3289:26=TÞð1000 6 T 6 3000Þ kP1 ¼ 1098:88T 3:92 expð5561:20=TÞð200 6 T 6 1400Þ kP1 ¼ 5:04 107 T 1:46 expð346:04=TÞð1400 < T 6 3000Þ
Fig. 8. Calculated overall rate coefficients for the CH2@CHCH2Br + OH reaction in a pressure range of 1014–1014 Torr of He bath gas at T = 298 K, 1000 K and 3000 K, respectively.
No pressure-dependence studies for the CH2@CHCH2Br + OH reaction were reported previously. The total rate constant and branching ratio have been calculated in the wide pressure range of
Fig. 9. Branching ratios for the CH2@CHCH2Br + OH reaction n a pressure range of 1014–1014 Torr of He bath gas at T = 298 K, 1000 K and 3000 K, respectively.
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Y. Zhang et al. / Computational and Theoretical Chemistry 1102 (2017) 114–126 Table 2 The parameters for the first 10 excited states of all the intermediates in the title reaction. Species parameters
Excited state 1 2
3
4
5
6
7
8
9
10
CR1
k (nm) f Excitation energies(eV)
3019.22 0.0000 0.4106
329.77 0.0007 3.7598
292.99 0.0712 4.2316
263.11 0.0114 4.7123
241.37 0.0057 5.1368
238.02 0.0003 5.2090
219.94 0.0000 5.6372
215.28 0.0000 5.7592
202.38 0.0049 6.1262
197.27 0.0020 6.2849
IM1
k(nm) f Excitation energies(eV)
333.76 0.0003 3.7148
332.29 0.0017 3.7312
266.49 0.0014 4.6525
257.91 0.0369 4.8073
239.00 0.0340 5.1875
217.07 0.0023 5.7117
214.91 0.0141 5.7691
209.51 0.0004 5.9178
208.13 0.0118 5.9572
206.72 0.0058 5.9976
IM2
k(nm) f Excitation energies(eV)
244.00 0.0009 5.0814
231.03 0.0167 5.3666
228.16 0.0013 5.4342
221.43 0.0011 5.5992
216.67 0.0068 5.7223
209.58 0.0007 5.9158
207.66 0.0017 5.9705
202.27 0.0142 6.1298
200.33 0.0012 6.1889
197.15 0.0064 6.2889
IM3
k(nm) f Excitation energies(eV)
327.32 0.0011 3.7878
317.37 0.0003 3.9066
271.59 0.0360 4.5651
237.03 0.0044 5.2307
226.91 0.0108 5.4640
217.76 0.0581 5.6937
208.15 0.0055 5.9564
205.98 0.0007 6.0191
204.39 0.0024 6.0659
199.06 0.1039 6.2285
IM4
k(nm) f Excitation energies(eV)
313.48 0.0036 3.9551
258.84 0.0000 4.7900
243.31 0.0018 5.0958
228.69 0.0020 5.4214
224.86 0.0104 5.5140
222.38 0.0521 5.5754
213.69 0.0177 5.8021
199.29 0.0001 6.2212
195.31 0.0001 6.3480
194.37 0.0049 6.3787
IM5
k(nm) f Excitation energies(eV)
3193.25 0.0001 0.3883
338.18 0.0007 3.6662
268.22 0.0042 4.6225
262.03 0.0037 4.7316
221.15 0.0001 5.6064
217.74 0.0001 5.6941
208.45 0.0191 5.9479
202.62 0.0004 6.1190
199.57 0.0010 6.2125
190.49 0.0036 6.5087
IM6
k(nm) f Excitation energies(eV)
298.65 0.0046 4.1514
278.97 0.0041 4.4444
263.99 0.0065 4.6966
243.15 0.0204 5.0991
238.36 0.0032 5.2016
222.02 0.0008 5.5844
220.31 0.0003 5.6278
216.80 0.0012 5.7188
211.64 0.0030 5.8583
211.00 0.0026 5.8761
IM7
k(nm) f Excitation energies(eV)
3529.40 0.0001 0.3513
355.72 0.0014 3.4854
289.89 0.0004 4.2769
285.12 0.0025 4.3485
220.88 0.0047 5.6133
218.60 0.0140 5.6717
217.47 0.0015 5.7013
201.70 0.0014 6.1470
199.72 0.0022 6.2078
198.47 0.0057 6.2470
IM8
k(nm) f Excitation energies(eV)
305.91 0.0025 4.0530
262.98 0.0009 4.7145
241.58 0.0013 5.1322
227.33 0.0145 5.4540
220.91 0.0324 5.6125
214.33 0.0052 5.7847
202.38 0.0032 6.1262
200.95 0.0042 6.1700
199.02 0.0006 6.2299
193.66 0.0002 6.4021
IM9
k(nm) f Excitation energies(eV)
428.97 0.0003 2.8903
420.28 0.0003 2.9500
329.02 0.0399 3.7683
306.59 0.0118 4.0439
254.42 0.0006 4.8732
240.54 0.1041 5.1545
235.72 0.1786 5.2599
228.10 0.0161 5.4354
223.36 0.0890 5.5508
210.88 0.0001 5.8794
1014–1014 Torr at the selected temperatures 298, 1000 and 3000 K, respectively. The calculated results were listed in Figs. 8 and 9, respectively. It can be seen from Fig. 8 that there was a typical falloff behavior for the complex forming reactions. With the temperature increasing, the falloff range shifts to the low pressure. At 298 K, the falloff region for the total rate constants is 103 to 101 Torr. At 1000 and 3000 K, the falloff region moves to lower pressures (106 to 102 Torr and 109 to 104 Torr, respectively). Meanwhile, the individual rate constants are sensitive to the pressure. Fig. 9 reveals that at 298 K, the major products are IM3 (CH2OHCHBrCH2) at lower and moderate pressures (e.g., P < 102 Torr), at the higher pressures, the stabilization of intermediate IM1(CH2OHCHCH2Br) becomes dominant; at 1000 K, the production of P1(CH2OH + CH2CHBr) and h-P1 (CH2CHCHBr + H2O) are the major reaction channel at P < 1 Torr, h-P1 (CH2CHCHBr + H2O) and IM3 are the major products at 1–104 Torr, At higher pressure, the dominant channel is the stabilization of the IM1(CH2OHCHCH2Br) and h-P1 (CH2CHCHBr + H2O); the hydrogen abstraction channel from the ACH2Br group of CH2@CHCH2Br is the dominant channel at the whole pressure range at 3000 K, respectively. All of these theoretical predictions must await future experimental verification. 3.4. UV–visible spectroscopy The Ultraviolet visible spectra analysis of the important species in the OH + CH2@CHCH2Br reaction has been conducted using the time dependent density functional theory (TD-DFT) at the M062X/6-311++G(d,p) level based on the ground-state optimized structures. The fluorescent properties of a molecule can be influenced by its light-absorption process. There are many stable intermediates generated in the title reaction. In order to get their
photolysis information in the sunlight, the calculated wavelength of absorption (k), oscillator strength (f) and the excitation energies for first ten excited states of are illustrated in Table 2. It is well known that when the excitation energies above 4.13 eV (about 300 nm), the compound is regarded to be photolyzed in the sunlight. It can be seen from Table 2 that the first excitations of IM1 (CH2(OH)CHCH2Br), IM2(CH2CH(OH)CH2Br), IM3(CH2OHCHBrCH2), IM4(CH2OHCH2CHBr), IM6 (CHOHCH2CH2Br), IM8 and IM9, happen at 333 nm (3.7148 eV), 244 nm (5.0814 eV), 327 nm (3.7878 eV), 313 nm (3.9551 eV), 298 nm (4.1514 eV), 305 nm (4.0530 eV) and 428 nm (2.8903 eV), respectively. Moreover, all the oscillator strengths of the excited states of the above species are above 0.0002, which indicated that they could easily undergo photolysis in the sunlight. Therefore, they have received significant attention in the photochemistry of the brominated organic compounds produced by CH2@CHCH2Br + OH reaction, specifically their wave-length dependence.
4. Conclusions The potential energy surfaces (PES) for the CH2@CHCH2Br + OH reaction were systematically characterized at both the M06-2X and CCSD(T) levels. The calculated results revealed that the CH2@CHCH2Br + OH reaction takes place via the abstraction and addition/elimination mechanisms. The barrierless interaction of the two reactants leads to a pre-reactive complex, which bifurcates into two different pathways leads to two energy-rich adducts (IM1 and IM2) with excess energy, which can react further to decomposition or rearrangements. The variational transition state theory and the RRKM theory is employed to calculated the kinetics
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of the title reaction over the temperature range of 200–3000 K and the pressure range of 1014–1014 Torr. It is concluded that the stabilization of the adduct IM3 (CH2OHCHBrCH2) and P1 (CH2OH + CH2CHBr) dominate the reaction at 200–700 K and 700–1000 K, respectively. The rate constant shows a weak temperature dependence. The abstraction pathway from the ACH2Br group of CH2@CHCH2Br becomes dominant at higher temperatures. The rate constant shows a strong temperature dependence. Meanwhile, the total rate constant exhibits an obvious falloff behavior. Timedependent DFT (TD-DFT) calculations indicate that IM1-IM4, IM6, IM8 and IM9 take photolysis easily in the sunlight, once they are generated. Acknowledgments This work is supported by the National Natural Science Foundation of China (No. 21507027), the Youth Fund Project of HuBei Provincial Department of Education (Q20132501) and Hubei Key Laboratory of Pollutant Analysis & Reuse Technology Open Fund (PA160204). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.comptc.2017.01. 005. References [1] W.T. Tsai, Environmental risk assessment of hydrofluoroethers (HFEs), J. Hazard. Mater. 119 (2005) 69–78. [2] Scientific Assessment of ozone depletion, World Meteorological Organization. Report No. 25, Geneva, Switzerland, 1991. [3] J. Albaladejo, B. Ballesteros, E. Jimenez, Y. Diaz de Mera, E. Martinez, Gas-phase OH radical-initiated oxidation of the 3-halopropenes studied by PLP-LIF in the temperature range 228–388 K, Atmos. Environ. 37 (2003) 2919–2926. [4] J. Albaladejo, A. Notario, C.A. Cuevas, B. Ballesteros, E. Martinez, A pulsed laser photolysis-resonance fluorescence kinetic study of the atmospheric Cl atominitiated oxidation of propene and a series of 3-halopropenes at room temperature, J. Atmos. Chem. 45 (2003) 35–50. [5] R. Atkinson, S.M. Aschmann, M.A. Goodman, Kinetics of the gas-phase reactions of NO3 radicals with a series of alkynes, haloalkenes, and abunsaturated aldehydes, Int. J. Chem. Kinet. 19 (1987) 299–307. [6] Y. Gai, M. Ge, W. Wang, Kinetic studies of O3 reactions with 3-bromopropene and 3-iodopropene in the temperature range 288–328 K, Atmos. Environ. 43 (2009) 3467–3471.
[7] M.J. Frisch, G.W. Trucks, H.B. Schlegel, P.W.M. Gill, B.G. Johnson, M.A. Robb, J.R. Cheeseman, T.A. Keith, G.A. Petersson, J.A. Pople, et al., Gaussian 09, Gaussian Inc., Wallingford, CT, 2010. [8] Y. Zhao, D.G. Truhlar, The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functional, Theor. Chem. Account. 120 (2008) 215–241. [9] Y. Zhao, D.G. Truhlar, Density functionals with broad applicability in chemistry, Acc. Chem. Res. 41 (2008) 157–167. [10] C. Gonzalez, H. Bernhard Schlegel, An improved algorithm for reaction path following, J. Chem. Phys. 90 (1989) 2154–2161. [11] C. Gonzalez, H.B. Schlegel, An improved algorithm for reaction path following, J. Chem. Phys. 90 (1989) 2154–2161 (Reaction path following in massweighted internal coordinates. J. Phys.Chem. 94 (1990) 5523-5527). [12] K. Raghavachari, G.W. Trucks, J.A. Pople, M. Head-Gordon, A fifth-order perturbation comparison of electron correlation theories, Chem. Phys. Lett. 157 (1989) 479–483. [13] K.A. Holbrook, M.J. Pilling, S.H. Robertson, Unimolecular Reactions, Wiley, Chichester, UK, 1996. [14] H. Hou, B.S. Wang, Ab initio study of the reaction of propionyl (C2H5CO) radical with oxygen (O2), J. Chem. Phys. 127 (2007) 054306–054314. [15] H. Hou, B.S. Wang, Y.S. Gu, Ab initio mechanism and multichannel RRKMTST rate constant for the reaction of Cl(2P) with CH2CO (Ketene), J. Phys. Chem. A 104 (2000) 320. [16] Y.J. Zhang, K. Chao, J.Y. Sun, Z.M. Su, X.M. Pan, J.P. Zhang, R.S. Wang, Theoretical study on the gas phase reaction of allyl alcohol with hydroxyl radical, J. Phys. Chem. A 117 (2013) 6629–6640. [17] S.H. Mousavipour, S. Ramazani, Z. Shahkolahi, Multichannel RRKM-TST and direct-dynamics VTST study of the reaction of hydroxyl radical with furan, J. Phys. Chem. A 113 (2009) 2838–2846. [18] Y.J. Zhang, K. Chao, X.M. Pan, J.P. Zhang, Z.M. Su, R.S. Wang, Mechanism and kinetic study of 3-fluoropropene with hydroxyl radical reaction, J. Mol. Graph. Model. 48 (2014) 18–27. [19] J.Y. Sun, R.S. Wang, B.H. Wang, Theoretical study on the gas phase reaction of acrylonitrile with a hydroxyl radical, Phys. Chem. Chem. Phys. 13 (2011) 16585–16595. [20] NIST Computational Chemistry Comparison and Benchmark Database.
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Computational and Theoretical Chemistry journal homepage: www.elsevier.com/locate/comptc
Theoretical Study on the Gas Phase Reaction of Allyl Bromide with Hydroxyl Radical Yunju Zhang a,⇑, Yuxi Sun a, Jingyu Sun b, Rongshun Wang c a
Key Laboratory of Photoinduced Functional Materials, Mianyang Normal University, Mianyang 621000, PR China Hubei Collaborative Innovation Center for Rare Metal Chemistry, Hubei Key Laboratory of Pollutant Analysis & Reuse Technology, College of Chemistry and Chemical Engineering, Hubei Normal University, Cihu Road 11, Huangshi, Hubei 435002, PR China c Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Renmin Road 5268, Changchun, Jilin 130024, PR China b
a r t i c l e
i n f o
Article history: Received 13 November 2016 Received in revised form 31 December 2016 Accepted 5 January 2017 Available online 6 January 2017 Keywords: OH Allyl bromide Reaction mechanism Rate constants Photolysis
a b s t r a c t Mechanisms and reaction channels of the allyl bromide (CH2@CHCH2Br) with OH reaction are studied using quantum chemistry. It is predicted that the H(or Br)-abstraction and addition/elimination mechanisms have been revealed on potential energy surface (PES). Direct H-abstract from the ACH2Br group of CH2@CHCH2Br leading to h-P1 (CH2CHCHBr + H2O) is dominant. As for addition/elimination mechanism, it is shown that the reaction is initiated by the addition of OH radical to the C@C bond of CH2@CHCH2Br to barrierlessly generate the intermediates IM1 and IM2, respectively. Multichannel RRKM theory and variational transition-state theory (VTST) are employed to evaluate the rate constants of temperature- and pressure-dependent. The calculated rate constants are in good agreement with the available experimental data. At 100 Torr with helium as bath gas, IM3 (CH2OHCHBrCH2) formed by collisional stabilization and the final products P1 (CH2OH + CH2CHBr) are the major product in the temperature range of 200– 700 K and 700–1000 K, respectively. The production of CH2@CHCHBr via hydrogen abstraction becomes dominant at high temperatures (T P 1000 K). Time-dependent DFT (TD-DFT) calculations indicate that IM1-IM4, IM6, IM8 and IM9 take photolysis easily in the sunlight at the wavelength of 333 nm, 244 nm, 327 nm, 313 nm, 298 nm, 305 nm and 428 nm, once they are generated. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Halogenated organic contaminants (HOCs) mainly include the fluorinated organic compounds (FOCs), chlorinated organic compounds (COCs) and brominated organic compounds (BOCs), which show the characteristics of persistent organic pollutants in environment. Chlorinated organic compounds and brominated organic compounds contain either chlorine or bromine atoms, and thus have ozone depletion potential (ODP) [1]. Because bromine atoms and brominated organic compounds are estimated to be 40–50 times more effective than chlorine atoms and chlorinated organic compounds in ozone destruction, brominated organic compounds are particularly problematic in processes related to climate changes and play a significant role in the depletion of the stratospheric ozone [2]. Allyl bromide is widely used in industrial and agricultural production as raw materials, solvents and so on, and it can be released into environment through a variety of wastewater streams. In addition to their environmental effects, a number of studies have reported that health effects have also been identified. ⇑ Corresponding author. http://dx.doi.org/10.1016/j.comptc.2017.01.005 2210-271X/Ó 2017 Elsevier B.V. All rights reserved.
For example, allyl bromide could irritate eyes, skin and respiratory system. Experimentally, the reactions involving allyl bromide (CH2@CHCH2Br) with many radicals and molecules have been investigated extensively, including reactions such as CH2@CHCH2Br with OH, Cl, NO3, O3 [3–6], respectively, which indicating that the dominant atmospheric loss pathway for allyl bromide may be reaction with OH radical. Up to date, only one experimental kinetic study have been reported the reaction of OH with CH2@CHCH2Br. In 2003, Albaladejo and Ballesteros [3] measured the rate constant to be of the reaction OH þ CH2 @CHCH2 Br ! products (3.6 ± 1.5) 1012 exp(3783 ± 964/RT) cm3 molecules1 s1 at P = 100 Torr and in the temperature range 228–388 K using the pulsed laser photolysis/laser-induced fluorescence technique. However, the detailed mechanisms of the degradation products of allyl bromide in atmosphere are unclear for the title reaction. Therefore, in order to detailed understand mechanistic and kinetic of the OH + CH2@CHCH2Br reaction and understand the chemical reactivity of CH2@CHCH2Br with OH in the atmospheric conditions, it is necessary to present the mechanistic and kinetic studies for the reaction of OH with CH2@CHCH2Br in this work.
Y. Zhang et al. / Computational and Theoretical Chemistry 1102 (2017) 114–126
2. Computational methods Electronic structure calculations are performed with Gaussian 09 program package [7]. The optimized geometries and harmonic frequencies of all the stationary points are obtained at the M06-2X [8,9]/6-311++G(d,p) level. The nature of all stationary structure is verified by harmonic vibrational frequency calculations, namely, equilibrium species possess all real frequencies; transition states (TS) possess only one imaginary frequency. The zero-point energy (ZPE) corrections are obtained at the same level. The transition states were subjected to intrinsic reaction coordinate (IRC) [10,11] calculations to confirm connection with designated intermediates. To prove the energy prediction, the CCSD(T) [12] method with the cc-pVTZ basis set was used to calculate the single point energies based on the M06-2X/6-311++G(d,p) optimized geometries. We choose the important product channels to calculate the rate constants using the variational transition-state theory (VTST) and multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) theory [13]. In the section of the kinetic calculations, we employed the modified computer program written by Hou and Wang for the OH with allyl bromide reaction [14], and this methodology has been successfully used to deal with the complex reactions [15–19]. 3. Results and discussion The optimized structures of stationary points (the complex, intermediates, transition states, reactant and products) are listed in Figs. 1–3, along with the available experimental values, respectively. As seen in Fig. 3, the calculated bond lengths and angles at the M06-2X/6-311++G(d,p) level are in good agreement with experimental data [20], indicating that the M06-2X/6-311++G(d, p) method is suitable for predicting the geometry of the title reaction. To clarify the reaction mechanism, the potential energy surface (PES) for this reaction at CCSD(T)/cc-pVTZ//M06-2X/6-311++ G(d,p) is described in Fig. 4. The ZPE, relative energies, reaction enthalpies and Gibbs free energy for all the stationary points are listed in Table 1. Table S1 displays the harmonic vibrational frequencies and the moment of inertia (au) of all species, respectively. The frequencies of CH2CHOH, CH2CHBr, CH3CHO, CH2OH, CH2O, CH3, H2O, HOBr and OH are in agreement with experimental data [20]. Unless mentioned otherwise, the geometric parameters used in the discussion are the M06-2X/6-311++G(d,p) results, and the energies used are at the CCSD(T)/cc-pVTZ + ZPE level. 3.1. Reaction mechanism As the OH radical can have either abstraction or addition/elimination mechanism, two distinguishable type initial attacks have been revealed for the radical–molecule reaction OH + CH2@CHCH2Br, namely, the attack on H (or Br) atom and the addition to the C@C double bond (addition–isomerization–elimination). A detailed discussion on the title reaction mechanisms is given as follows. 3.1.1. Initial association The OH-allyl bromide surface is characterized by two bound intermediates, denoted as IM1 and IM2. The initial step involves the addition of the OH radical to the C atom of the C@C bond of CH2@CHCH2Br, generating the relatively stable radicals IM1 (CH2OHCHCH2Br) and IM2 (CH2CHOHCH2Br), respectively. The reaction coordinate is complicated by an initial energy minimum at CR1, which is a weakly bound complex with a 2.38 kcal/mol barrier to further rearrangement. This typical phenomenon is also proposed by Singleton and Cvetanovic et al [21]. Therefore, the reaction of OH with allyl bromide to form IM1 and IM2 is effectively without barrier. After formed the CR1, the oxygen atom of the
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OH radical should rotate and add to the carbon atom of C@C double bond in CH2@CHCH2Br via TS1 and TS2 to form IM1 and IM2, and the corresponding barrier heights are calculated to be 3.07 and 1.31 kcal/mol, respectively. The relative energy of TS1 is 1.76 kcal/mol higher than that of TS2, Moreover, the DG (298 K) data for the OH addition to the central-carbon atom (TS2) is 1.22 kcal/mol lower than that addition to the terminal-carbon atom (TS1) of the C@C double bond. These results indicate that the center Caddition is slightly preferred over the terminal C-addition addition. As seen in Fig. 4 and Table 1, the formation of IM1 and IM2 are thermodynamically favorable. In the following part, we will focus on discussing the formation pathways of various products which associated with IM1 and IM2, respectively. 3.1.2. The unimolecular reaction of IM1 3.1.2.1. The CH2OH radical formation channel. Clearly, from IM1 (29.32), there are two feasible pathways to form P1 (CH2OH + CH2CHBr). They can be written as follows
PathP1ð1ÞR ! CR1 ! IM1 ! IM3 ! P1ðCH2 OH þ CH2 CHBrÞ PathP1ð2ÞR ! CR1 ! I M1 ! IM4 ! P1ðCH2 OH þ CH2 CHBrÞ IM1 can undergo a 1,2-Br shift to form IM3 (CH2OHCHBrCH2) via transition state TS3 as shown in Path P1(1), or 1,2-H shift to form IM4 (CH2OHCH2CHBr) via transition state TS4 as shown in Path P1(2), respectively. Finally, both IM3 and IM4 can dissociate to P1 via CAC bond rupture corresponding transition state TS5 and TS6, respectively. For IM1 ? P1 conversion, two barriers must be surmounted in Path P1(1), which are 1.60 and 32.53 kcal/mol for the steps of IM1 ? IM3 and IM3 ? P1, respectively, it should be noted that the barrier of IM1 ? IM3 is the lowest barrier among all the subsequent reaction channels of IM1 and IM2; while in Path P1 (2), the barriers are 43.64 (IM1 ? IM4) and 28.13 (IM4 ? P1) kcal/mol, respectively. Due to the higher isomerization barrier, we expect that Path P1(2) should be less competitive with Path P1(1). 3.1.2.2. The CH2O radical formation channel. The hydrogen atom of the OH group in IM1 is migrating to the C-central atom via TS7 to form another intermediate IM5 (CH2OCH2CH2Br). The barrier height for IM1 ? IM5 is about 33.76 kcal/mol, which is 9.88 kcal/mol lower than TS4, and 32.16 kcal/mol higher than TS3. Subsequently, IM5 decomposes to form the final products P2 (CH2O + CH2CH2Br) via transition state TS8. The formation pathway of P2 can be written as
PathP2R ! CR1 ! IM1 ! IM5 ! P2ðCH2 O þ CH2 CH2 BrÞ The barrier height for this step is 17.12 kcal/mol. However, TS8 is still lower than the reactants by 6.04 kcal/mol and TS1 by 6.73 kcal/mol, which indicating that P2 is easily yielded once IM5 is formed by increasing temperatures. 3.1.2.3. The CH2Br radical formation channel from IM1. Starting from IM1, only one feasible channel is associated with the formation of CH2Br radical, which can be written as
PathP3ð1ÞR ! CR1 ! IM1 ! IM6 ! P3ðCH2 Br þ CH2CHOHÞ IM1 can isomerize to IM6 (CHOHCH2CH2Br) via a triangular structure transition state TS9. The barrier height of TS9 is 39.10 kcal/mol with respect to IM1, which is 5.34 kcal/mol higher than TS7 and 37.50 kcal/mol higher than TS3, as well as higher than TS1 9.09 kcal/mol. IM6, -30.36 kcal/mol relative to the initial reactants, breaks the CAC bond to give rise to P3 (CH2Br + CH2CHOH) via TS10 surmounting a 29.12 kcal/mol barrier height. Evidently, the ratedetermining step for the formation of P3 in Path P3(1) is the Hshift step, i.e., IM1 ? TS9 ? IM6, because the barriers for the entrance and decomposition steps TS1 and TS10 are both lower
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Fig. 1. Optimized geometries of species which connected to IM1 for the reaction of the CH2@CHCH2Br + OH reaction at M06-2X/6-311++(d,p) level.
than TS9. Moreover, due to higher isomerization barriers, this pathway should not play an important role at low and moderate temperatures, as confirmed by the kinetic calculation.
3.1.2.4. The H-atom formation channel from IM1. There are three feasible H-atom formation pathways from IM1, which can be depicted as
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Fig. 2. Optimized geometries of species which connected to IM1 for the reaction of the CH2@CHCH2Br + OH reaction at M06-2X/6–311++(d,p) level.
PathP4R ! CR1 ! IM1 ! P4ðH þ CHOHCHCH2 BrÞ
PathP5ð2ÞR ! CR1 ! IM1 ! IM6 ! P5ðH þ CH2 BrCH2 CHOÞ
PathP5ð1ÞR ! CR1 ! IM1 ! IM5 ! P5ðH þ CH2 BrCH2 CHOÞ
The IM1 ? IM5 and IM1 ? IM6 in Path P5(1) and Path P5(2) are two hydrogen migration processes, which are the same as that in
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Fig. 3. Optimized geometries of reactants and products for the reaction of the CH2@CHCH2Br + OH reaction at M06-2X/6-311++(d,p) level. Bond distances are in angstroms, and angles are in degrees. The values in italics are experimental data from ref 20.
Path P2 and Path P3(1), respectively. IM1, IM5 and IM6 can eliminate H atom to form two different products P4 (H + CHOHCHCH2Br) and P5 (H + CHOCH2CH2Br) via TS11, TS12 and TS13 via surmounting 35.66, 23.27 and 35.68 kcal/mol energy barriers, respectively. The relative energy of TS11 is 1.90 kcal/mol higher than that of the rate-determining transition state TS7 in Path P5(1), and is 3.44 kcal/mol lower than that of the rate-determining transition state TS9 in Path P5(2), respectively. Therefore, in view of the relative energies of rate-determining transition states and the simplicity, the pathway of Path P5(2) cannot compete with Path P4 and Path P5(1). 3.1.3. The unimolecular reaction of IM2 3.1.3.1. The CH2Br radical formation channel. For the CH2Br radical formation channels, two reaction scenarios are possible from IM2
Path P3ð2Þ R ! CR1 ! IM2 ! P3 ðCH2 Br þ CH2 CHOHÞ Path P6 R ! CR1 ! IM2 ! IM7 ! P6ðCH2 Br þ CH3 CHOÞ One is the direct decomposition of IM2 to the final products P3 via transition state TS14. This CAC bond fission barrier is quite low, i.e., 28.88 kcal/mol, which is the lowest barriers on the PES from IM2. Therefore, this formation of P3 channel should be the dominant pathway of IM2. The other minor reaction channel of IM2 involves the formation of another local minimum IM7 (CH3CHOCH2Br) via a 1,3-H shift transition state TS15. The barrier for this isomerization channel is 32.46 kcal/mol, which is 3.58 kcal/mol higher than that of TS14. After IM7 is formed, the CAC bond can dissociate to P6 (CH2Br + CH3CHO) involved transition state TS16. This cleavage process needs to surmount 15.56 kcal/mol barrier. TS16 is about
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Fig. 4. The profile of PES for the CH2@CHCH2Br + OH reaction at the CCSD(T)/cc-pVTZ//M06-2X/6-311++G(d,p) level, (a) terminal-C addition (b) central-C addition (c) abstraction, respectively.
8.98 kcal/mol lower than the reactants and 12.62 kcal/mol lower than TS15, therefore, once IM7 is generated, P6 is easily yielded by increasing temperatures. However, the rather higher isomer-
ization barrier of IM2 ? TS15 ? IM7 makes the pathway Path P6 far from competitive with pathway Path P3(2) under normal conditions.
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Table 1 Relative Energies(DE), Reaction Enthalpies(DH) and Gibbs Free Energy(DG) at 298 K for all the species in the CH2@CHCH2Br + OH reaction (energies in kcal/mol).
a b
Species
ZPE
DE a
DEb
DH0298 b
DG b
R:(CH2@CHCH2Br + OH) P1:(CH2OH + CH2CHBr) P2:(CH2O + CH2CH2Br) P3:(CH2Br + CH2CHOH) P4:(H + CHOHCHCH2Br) P5:(H + CHOCH2CH2Br) P6:(CH2Br + CH3CHO) P7:(CH3 + CH2BrCHO) P8:(CH3 + CHOHCHBr) P9:(H + CH2COHCH2Br) P10:(H + CH3COCH2Br) P11:(H + CH3COHCHBr) h-P1:(CH2CHCHBr + H2O) h-P2:(CH2CCH2Br + H2O) h-P3:(CHCHCH2Br + H2O) Br-P1:(CH2CHCH2 + HOBr) CR1 IM1 IM2 IM3 IM4 IM5 IM6 IM7 IM8 IM9 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 TS9 TS10 TS11 TS12 TS13 TS14 TS15 TS16 TS17 TS18 TS19 TS20 TS21 TS22 TS23 TS24 h-TS1 h-TS2 h-TS3 Br-TS1
0.00 50.21 49.79 50.08 48.41 47.89 49.35 48.40 49.00 47.98 47.51 47.57 49.67 49.47 49.79 49.76 51.69 54.55 53.61 54.32 54.33 54.26 54.53 53.36 53.86 54.01 51.76 51.94 54.23 51.16 51.60 51.93 51.68 51.94 51.33 51.82 49.34 49.16 48.87 51.53 51.16 51.78 51.38 50.80 51.13 48.98 48.80 50.92 48.44 49.09 48.74 48.63 48.26 51.12
0.00 6.82 15.04 10.36 1.86 8.07 20.06 15.66 11.82 2.91 13.48 6.96 32.28 12.86 6.18 7.13 4.77 33.50 32.50 34.73 30.86 26.59 34.22 27.69 33.63 45.79 0.76 2.54 32.74 10.04 1.14 3.14 2.18 8.70 1.72 3.97 3.35 3.15 1.88 2.61 1.78 11.03 9.44 8.88 2.52 4.54 5.49 1.54 3.27 0.08 0.12 2.58 4.68 12.68
0.00 5.67 13.92 9.45 1.21 6.70 20.14 15.99 11.06 0.61 11.68 4.76 31.42 10.28 4.12 7.36 2.38 29.32 28.82 30.52 27.97 23.16 30.36 24.54 30.91 40.10 0.69 1.07 27.72 14.32 2.01 0.16 4.44 6.04 9.78 1.24 6.34 0.11 5.32 0.06 3.64 8.98 7.24 11.78 0.58 6.62 3.10 6.82 0.78 2.10 0.69 3.58 5.98 11.75
0.00 5.78 13.95 9.54 1.20 6.67 20.02 15.69 10.88 0.62 11.48 4.58 31.22 9.82 3.79 5.60 2.64 30.35 29.87 31.66 28.96 24.52 31.55 25.49 31.90 40.82 0.08 2.03 29.09 13.34 1.13 0.71 2.96 7.17 8.55 2.04 5.31 1.09 4.30 0.80 2.10 9.98 8.23 10.42 1.39 5.52 4.14 5.70 1.63 1.02 0.09 2.90 5.36 11.15
0.00 8.04 15.90 11.92 4.06 4.06 22.98 16.70 11.48 2.34 9.26 1.92 32.02 11.28 4.98 11.14 5.21 20.93 19.87 21.40 19.42 14.41 21.49 16.26 22.12 31.88 8.69 7.47 18.66 22.86 10.52 8.34 13.35 2.52 18.46 6.60 15.14 8.90 13.89 8.50 12.93 0.62 1.36 20.87 8.02 15.60 5.54 15.70 7.59 11.16 8.28 11.44 13.81 19.93
M06-2X/6-311++G(d,p) level. CCSD(T)/cc-pVTZ//M06-2X/6-311++G(d,p) level.
3.1.3.2. The CH3 radical formation channel. For the CH3 radical formation channels, two pathways are energetically possible, which can be depicted as:
Path P7 R ! CR1 ! IM2 ! IM7 ! P7ðCH3 þ CH2 BrCHOÞ Path P8 R ! CR1 ! IM2 ! IM8 ! P8ðCH3 þ CHOHCHBrÞ The formation of IM7 is the same as that in Path P6. Subsequently, IM7 can further decompose to form P7 (CH3 + CH2BrCHO) via TS17, as in Path P7. The barrier for the step of IM7 ? P7 conversion is 17.30 kcal/mol. This bond cleavage path is exothermic by 15.69 kcal/mol. Compared with the formation of P6, P7 are less
stable than P6. Furthermore, the barrier height of TS17 is 1.74 kcal/mol higher than of TS16. Therefore, the formation of P6 channel occurs more preferentially than the formation of P7 channel. In Path P8, IM2 can transform to IM8 (CH3CHOHCHBr) via a four-membered-ring transition state TS18. The barrier height is 40.60 kcal/mol, which is higher than TS14 by 11.72 kcal/mol and TS15 by 8.14 kcal/mol, respectively. IM8, 30.91 kcal/mol relative to the initial reactants, can break the CAC bond to give rise to P8 (CH3 + CHOHCHBr) via TS19. The barrier height is 30.33 kcal/mol, which is 13.03 kcal/mol higher than that of the IM7 ? P7 conversion. These results indicate that the Path P8 occurs less favorable than the Path P7.
Y. Zhang et al. / Computational and Theoretical Chemistry 1102 (2017) 114–126
3.1.3.3. The H-atom formation channel. There are four H-atom formation pathways through IM2 which can transform to the corresponding product.
Path P9R ! CR1 ! IM2 ! P9 ðH þ CH2 COHCH2 BrÞ Path P10ð1Þ R ! CR1 ! IM2 ! IM7 ! P10ðH þ CH3 COCH2 BrÞ Path P10ð2Þ R ! CR1 ! IM2 ! IM9 ! P10ðH þ CH3 COCH2 BrÞ Path P11 R ! CR1 ! IM2 ! IM8 ! P11ðH þ CH3 COHCHBrÞ For the above four H-elimination pathways, which have the same steps of R ? CR1 ? IM2, and subsequently, isomer IM2 transforms to three different of products via four different reaction pathways. (i) In Path P9, IM2 can take CAH bond rupture leading to P9 (H + CH2COHCH2Br) via TS20. The dissociation barrier is 35.44 kcal/mol. (ii) The formation pathways of IM7 have been discussed in previous sections (in Path P6). For brevity, we decide not to discuss them again. IM7 can dissociate to P10 (H + CH3COCH2Br) via the CAH bond rupture transition state TS21 as in Path P10(1). The relative energy of rate-determining transition states TS15 in Path P10(1) is 2.98 kcal/mol lower than that of TS20 in Path P9, while 3.58 kcal/-
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mol higher than that of TS14 in Path P3(2). Therefore, in view of the relative energies of rate-determining transition states and the simplicity, we can conclude that Path P9 is less competitive than pathways Path P3(2) and P10(1), and Path P3(2) has priority over the pathway Path P10(1). (iii) In Path P10(2), a successive 1,2-H-shift and dissociation steps (IM2 ? IM9 ? P10) can also lead to product P10 (H + CH3COCH2Br) via transition states TS22 and TS23. It is an H-shift-H-elimination mechanism. Two high barriers need to be surmounted from IM2 to P10, that is, 35.64 and 39.32 kcal/mol for IM2 ? IM9 and IM9 ? P10 conversion, respectively. Because the rate-determining energy barrier (39.32) of Path P10(2) is higher than of Path P10(1) (32.46). Therefore, pathway Path P10(2) should be less competitive than pathway Path P10(1). (iv) For Path P11, the formation of IM8 is the same as that in Path P8. Subsequently, IM8 undergoes a H-elimination process to produce P11 (H + CH3COHCHBr) via TS24. The barrier for IM8 ? P11 conversion is 33.01 kcal/mol. Yet, the rate-determining energy barrier for Path P11 is 40.60 kcal/mol, which is 5.16, 8.14 and 1.28 kcal/mol higher than that of Path P9, Path P10(1) and Path P10(2), respectively. Therefore, from the kinetic consideration, for the above mentioned four H-elimination pathways, the order of reaction competition abilities is Path P10(1) > Path P9 > Path P10(2) > Path P11.
Fig. 5. Brief description of the progression on PES for the CH2@CHCH2Br + OH reaction.
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3.2. H-abstraction and Br-abstraction pathways As shown in Fig. 5, there are four different direct H (or Br) abstract pathways. The most favorable channel is the forming of h-P1 (CH2CHCHBr + H2O) via h-TS1. The energy of h-TS1 is only 0.69 kcal/mol higher than the reactants. The second and three channels corresponds to hydrogen abstraction channel by OH from the center C atom of -CH and -CH2 groups of CH2@CHCH2Br, leading to h-P2 (CH2CCH2Br + H2O) and h-P3 (CHCHCH2Br + H2O) via transition states h-TS2 and h-TS3 with the barrier height of 3.58 and 5.98 kcal/mol which is 2.89 and 5.29 slightly higher than that of h-TS1. The last pathway is abstracting the Br atom of CH2@CHCH2Br by OH radical to form the final product Br-P1 (HOBr + CH2CHCH2) via transition state Br-TS1. The calculated barrier height for this process is 11.75 kcal/mol, which are 11.06, 8.17 and 5.77 kcal/mol higher than h-TS1, h-TS2 and h-TS3, respectively. Moreover, the Gibbs energies (DG) of h-P2, h-P3 and Br-P1 are 20.74, 27.04 and 43.16 kcal/mol higher than that of h-P1, respectively. Obviously, the most feasible abstract channel is the formation of h-P1 among these four abstract pathways.
Scheme 2.
Scheme 3.
kP2 ðT; PÞ ¼
3.3. Kinetic calculation The kinetic calculation for the important reaction routes of the OH + CH2@CHCH2Br reaction (Schemes 1–3) is calculated by using the variational transition-state theory (VTST) and multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) theory on the basis of energetics, frequencies and moments of inertia of various relevant species. The reaction paths including in Schemes 1–3 are considered in the following calculation: where ‘‘⁄” represents the vibrational excitation of the intermediate (IMj). Steady-state assumption for energized intermediate (IMj⁄) leads to the following expressions (the detailed calculation processes are given in the Supporting information (Note S1)): For Scheme 1:
kIM1 ðT; PÞ ¼
kIM3 ðT; PÞ ¼
kIM5 ðT; PÞ ¼
kP1 ðT; PÞ ¼
aa
– Q– t Qr
– Q– t Qr
aa
aa
– Q– t Qr
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – k6 ðEÞ – Na ðE– ÞeE =RT dE X4 0
ð6Þ
X 3 ¼ k4 ðEÞ=ðk5 ðEÞ þ k8 ðEÞ þ xÞ X 4 ¼ X 1 k3 ðEÞ X 2 k5 ðEÞ X 3 For Scheme 2:
ð1Þ
kIM2 ðT; PÞ ¼
ð2Þ
kP3 ðT; PÞ ¼
ð3Þ
kP9 ðT; PÞ ¼
– Q– t Qr
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – k7 ðEÞX 2 – Na ðE– ÞeE =RT dE X 4 0
aa
ð5Þ
X 2 ¼ k2 ðEÞ=ðk3 ðEÞ þ k7 ðEÞ þ xÞ
– Q– t Qr
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – X3x – Na ðE– ÞeE =RT dE X 4 0
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – k8 ðEÞX 3 – N a ðE– ÞeE =RT dE X 4 0
With the following definition:
eEa =RT
h Q CH2 @CHCH2 Br Q OH Z 1 – X2x – Na ðE– ÞeE =RT dE X4 0
– Q– t Qr
X 1 ¼ k1 ðEÞ þ k2 ðEÞ þ k4 ðEÞ þ k6 ðEÞ þ x
eEa =RT
h Q CH2 @CHCH2 Br Q OH Z 1 – x – N a ðE– ÞeE =RT dE X4 0
aa
kP4 ðT; PÞ ¼
aa
aa
– Q– t Qr
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – x – Na ðE– ÞeE =RT dE X1 0
aa
– Q– t Qr
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – k2 ðEÞ – Na ðE– ÞeE =RT dE X1 0
aa
eEa =RT h Q CH2 @CHCH2 Br Q OH Z 1 – k3 ðEÞ – Na ðE– ÞeE =RT dE X 1 0
X 1 ¼ k1 ðEÞ þ k2 ðEÞ þ k3 ðEÞ þ x
Scheme 1.
ð8Þ
– Q– t Qr
With the following definition:
ð4Þ
ð7Þ
ð9Þ
Y. Zhang et al. / Computational and Theoretical Chemistry 1102 (2017) 114–126
The microcanonical rate constant is calculated using the RRKM theory as follows:
ki ðEÞ ¼ ai C i N i ðE– i Þ=hqj ðEj Þ
ð7Þ
In the above equations, aa is the statistical factor for the reaction path a, and ai is the statistical factor (degeneracy) for the ith reaction path; Ea is the energy barrier for the reaction step a. Q OH and Q CH2 @CHCH2 Br are the total partition function of OH and CH2– @CHCH2Br, respectively; Q – t and Q r are the translational and rotational partition functions of entrance transition state, respectively; N a ðE– Þ is the number of state for the association transition state with excess energy E– above the association barrier. ki ðEÞ is the energy-specific rate constant for the ith channel and Ci is the ratio of the overall rotational partition function of the TSi and IMj; N i ðE– i Þ is the number of states at the energy above the barrier height for transition state i; qj ðEj Þ is the density of states at energy Ej of the intermediate. The density of states and the number of states are
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calculated using the extended Beyer-Swinehart algorithm [22,23]. Where x = bcZLJ[M] and bc is the collision efficiency, which is calculated using Troe’s weak collision approximation [22] with the energy transfer parameter hDEi, The simple expression for collisional energy transfer (hDEi) [24,25] is
bc 1 bc1=2
ffi
hDEi F E kT
This expression holds nearly exactly at the weak collision limit hDEi FEkT for all collision models [24,25]. The factor FE is set to 1.0 empirically. The average energy transfer per collision, i.e., hDEi, is unknown and cannot be calculated quantitatively. In consideration of the experimental rate constants, it is found that the values around 100 cm1 for hDEi should be reasonable to calculate the rate constants. ZLJ is the Lennard-Jones collision frequency. The collision efficiency is estimated using the Lennard-Jones potential (V(r) = 4e[(r/r)12 (r/r)6]) by fitting the interaction energies calculated at the M06-2X/6-311++G(d,p) level for IM1. . .He and
Fig. 6. Arrhenius plots of the total and individual rate constants for the CH2@CHCH2Br + OH reaction at 100 Torr He.
Fig. 7. Branching ratios for the CH2@CHCH2Br + OH reaction, which correspond to Fig. 3 with a pressure of 100 Torr He.
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IM2. . .He. It is estimated that (e = 42.38 K, r = 2.82 Å) for IM1. . .He and (e = 27.81 K, r = 2.86 Å) for IM2. . .He, and [M] is the concentration of the bath gas M (He). The weak collision approximation is used for the intermediate. The rate coefficients for the direct hydrogen abstraction routes can be readily obtained using the conventional transition-state theory, viz.:
kabs ðTÞ ¼ j1
kB T Q– TS eE1 =ðRTÞ h Q CH2 @CHCH2 Br Q OH
where j1 is the tunneling factor, kB and h are Boltzmann and Planck constants, respectively. Q – TS , Q CH2 @CHCH2 Br and Q OH are the h-TS1 (hTS2 or h-TS3), CH2@CHCH2Br and OH partition functions, respectively. E1 is the energy barrier of h-TS1 (h-TS2 or h-TS3). The unsymmetrical Eckart potential model is employed to estimate j1 [26,27]. The rate coefficients are calculated as a function of temperature in the range of 200–3000 K. Arrhenius plots of the total and individual rate constants at the whole temperature range and at the pressure of 100 Torr, He are shown in Fig. 6, together with some of the available experimental data for comparison between our computed and the available experimental data. The calculated results reveal that our calculated total rate constants at 228– 388 K are in good agreement with the available experimental val-
ues. The product branching ratios for the title reaction are shown in Fig. 7. As can be seen from Fig. 7, the fraction of the IM3 depends strongly on temperature. i.e., from 96.7 at 200 K, 37.1% at 700 K, and decreasing to 2.28% at 1200 K. Temperature-dependence of the fraction of the H-abstract (from CH2Br group) and P1 (CH2OH + CH2CHBr) are more complicated. For H-abstract, first, it sharply rises with temperature and reaches a maximum of 66.3% at about T = 2200 K, and then almost linearly decreases when temperature increase further. Similar changes occur for P1, the fraction of P1 sharply rises with increasing temperatures first at 200–900 K, from 0 at 200 K up to maximal point of 44.9% at 900 K, but drops at T P 1000 K, from 44.1% at 1000 K down to 1.45% at 3000 K. From Fig. 7, we can see that P1 is dominant products at 700–1000 K; h-P1 and IM3 are the major products at T P 1000 K and 200– 700 K, respectively. Meanwhile, we have also provided the rate constants in the temperature range of 200–3000 K at atmospheric pressure P = 760 Torr as presented in Fig. S1, At T = 298 K and P = 760 Torr, the total rate constant is 1.77 1011 cm3 molecule1 s1. For practical use, the predicted total and important individual rate constants are fitted to a modified three parameter Arrhenius expression. The rate constants for the total (ktot) and the formations of kIM1, kIM2, kIM3, kh-TS1 and kP1 in units of cm3 molecule1 s1 are presented, respectively, as follows:
K tot ¼ 5:46 1014 T 3:27 expð6:08=TÞð200 6 T 6 500Þ K tot ¼ 8:79 1012 T 0:99 expð0:76=TÞð500 < T 6 3000Þ K IM1 ¼ 4:53 1017 T 3:76 expð2:14=TÞð200 6 T 6 3000Þ K IM2 ¼ 1:58 106 T 2:58 expð119:95=TÞð200 6 T 6 500Þ K IM2 ¼ 5:62 1012 T 1:36 expð2569:62=TÞð500 6 T 6 3000Þ K IM3 ¼ 3:15 109 T 1:02 expð171:32=TÞð200 6 T 6 3000Þ K hTS1 ¼ 2:14 1014 T 1:25 expð3289:26=TÞð1000 6 T 6 3000Þ kP1 ¼ 1098:88T 3:92 expð5561:20=TÞð200 6 T 6 1400Þ kP1 ¼ 5:04 107 T 1:46 expð346:04=TÞð1400 < T 6 3000Þ
Fig. 8. Calculated overall rate coefficients for the CH2@CHCH2Br + OH reaction in a pressure range of 1014–1014 Torr of He bath gas at T = 298 K, 1000 K and 3000 K, respectively.
No pressure-dependence studies for the CH2@CHCH2Br + OH reaction were reported previously. The total rate constant and branching ratio have been calculated in the wide pressure range of
Fig. 9. Branching ratios for the CH2@CHCH2Br + OH reaction n a pressure range of 1014–1014 Torr of He bath gas at T = 298 K, 1000 K and 3000 K, respectively.
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Y. Zhang et al. / Computational and Theoretical Chemistry 1102 (2017) 114–126 Table 2 The parameters for the first 10 excited states of all the intermediates in the title reaction. Species parameters
Excited state 1 2
3
4
5
6
7
8
9
10
CR1
k (nm) f Excitation energies(eV)
3019.22 0.0000 0.4106
329.77 0.0007 3.7598
292.99 0.0712 4.2316
263.11 0.0114 4.7123
241.37 0.0057 5.1368
238.02 0.0003 5.2090
219.94 0.0000 5.6372
215.28 0.0000 5.7592
202.38 0.0049 6.1262
197.27 0.0020 6.2849
IM1
k(nm) f Excitation energies(eV)
333.76 0.0003 3.7148
332.29 0.0017 3.7312
266.49 0.0014 4.6525
257.91 0.0369 4.8073
239.00 0.0340 5.1875
217.07 0.0023 5.7117
214.91 0.0141 5.7691
209.51 0.0004 5.9178
208.13 0.0118 5.9572
206.72 0.0058 5.9976
IM2
k(nm) f Excitation energies(eV)
244.00 0.0009 5.0814
231.03 0.0167 5.3666
228.16 0.0013 5.4342
221.43 0.0011 5.5992
216.67 0.0068 5.7223
209.58 0.0007 5.9158
207.66 0.0017 5.9705
202.27 0.0142 6.1298
200.33 0.0012 6.1889
197.15 0.0064 6.2889
IM3
k(nm) f Excitation energies(eV)
327.32 0.0011 3.7878
317.37 0.0003 3.9066
271.59 0.0360 4.5651
237.03 0.0044 5.2307
226.91 0.0108 5.4640
217.76 0.0581 5.6937
208.15 0.0055 5.9564
205.98 0.0007 6.0191
204.39 0.0024 6.0659
199.06 0.1039 6.2285
IM4
k(nm) f Excitation energies(eV)
313.48 0.0036 3.9551
258.84 0.0000 4.7900
243.31 0.0018 5.0958
228.69 0.0020 5.4214
224.86 0.0104 5.5140
222.38 0.0521 5.5754
213.69 0.0177 5.8021
199.29 0.0001 6.2212
195.31 0.0001 6.3480
194.37 0.0049 6.3787
IM5
k(nm) f Excitation energies(eV)
3193.25 0.0001 0.3883
338.18 0.0007 3.6662
268.22 0.0042 4.6225
262.03 0.0037 4.7316
221.15 0.0001 5.6064
217.74 0.0001 5.6941
208.45 0.0191 5.9479
202.62 0.0004 6.1190
199.57 0.0010 6.2125
190.49 0.0036 6.5087
IM6
k(nm) f Excitation energies(eV)
298.65 0.0046 4.1514
278.97 0.0041 4.4444
263.99 0.0065 4.6966
243.15 0.0204 5.0991
238.36 0.0032 5.2016
222.02 0.0008 5.5844
220.31 0.0003 5.6278
216.80 0.0012 5.7188
211.64 0.0030 5.8583
211.00 0.0026 5.8761
IM7
k(nm) f Excitation energies(eV)
3529.40 0.0001 0.3513
355.72 0.0014 3.4854
289.89 0.0004 4.2769
285.12 0.0025 4.3485
220.88 0.0047 5.6133
218.60 0.0140 5.6717
217.47 0.0015 5.7013
201.70 0.0014 6.1470
199.72 0.0022 6.2078
198.47 0.0057 6.2470
IM8
k(nm) f Excitation energies(eV)
305.91 0.0025 4.0530
262.98 0.0009 4.7145
241.58 0.0013 5.1322
227.33 0.0145 5.4540
220.91 0.0324 5.6125
214.33 0.0052 5.7847
202.38 0.0032 6.1262
200.95 0.0042 6.1700
199.02 0.0006 6.2299
193.66 0.0002 6.4021
IM9
k(nm) f Excitation energies(eV)
428.97 0.0003 2.8903
420.28 0.0003 2.9500
329.02 0.0399 3.7683
306.59 0.0118 4.0439
254.42 0.0006 4.8732
240.54 0.1041 5.1545
235.72 0.1786 5.2599
228.10 0.0161 5.4354
223.36 0.0890 5.5508
210.88 0.0001 5.8794
1014–1014 Torr at the selected temperatures 298, 1000 and 3000 K, respectively. The calculated results were listed in Figs. 8 and 9, respectively. It can be seen from Fig. 8 that there was a typical falloff behavior for the complex forming reactions. With the temperature increasing, the falloff range shifts to the low pressure. At 298 K, the falloff region for the total rate constants is 103 to 101 Torr. At 1000 and 3000 K, the falloff region moves to lower pressures (106 to 102 Torr and 109 to 104 Torr, respectively). Meanwhile, the individual rate constants are sensitive to the pressure. Fig. 9 reveals that at 298 K, the major products are IM3 (CH2OHCHBrCH2) at lower and moderate pressures (e.g., P < 102 Torr), at the higher pressures, the stabilization of intermediate IM1(CH2OHCHCH2Br) becomes dominant; at 1000 K, the production of P1(CH2OH + CH2CHBr) and h-P1 (CH2CHCHBr + H2O) are the major reaction channel at P < 1 Torr, h-P1 (CH2CHCHBr + H2O) and IM3 are the major products at 1–104 Torr, At higher pressure, the dominant channel is the stabilization of the IM1(CH2OHCHCH2Br) and h-P1 (CH2CHCHBr + H2O); the hydrogen abstraction channel from the ACH2Br group of CH2@CHCH2Br is the dominant channel at the whole pressure range at 3000 K, respectively. All of these theoretical predictions must await future experimental verification. 3.4. UV–visible spectroscopy The Ultraviolet visible spectra analysis of the important species in the OH + CH2@CHCH2Br reaction has been conducted using the time dependent density functional theory (TD-DFT) at the M062X/6-311++G(d,p) level based on the ground-state optimized structures. The fluorescent properties of a molecule can be influenced by its light-absorption process. There are many stable intermediates generated in the title reaction. In order to get their
photolysis information in the sunlight, the calculated wavelength of absorption (k), oscillator strength (f) and the excitation energies for first ten excited states of are illustrated in Table 2. It is well known that when the excitation energies above 4.13 eV (about 300 nm), the compound is regarded to be photolyzed in the sunlight. It can be seen from Table 2 that the first excitations of IM1 (CH2(OH)CHCH2Br), IM2(CH2CH(OH)CH2Br), IM3(CH2OHCHBrCH2), IM4(CH2OHCH2CHBr), IM6 (CHOHCH2CH2Br), IM8 and IM9, happen at 333 nm (3.7148 eV), 244 nm (5.0814 eV), 327 nm (3.7878 eV), 313 nm (3.9551 eV), 298 nm (4.1514 eV), 305 nm (4.0530 eV) and 428 nm (2.8903 eV), respectively. Moreover, all the oscillator strengths of the excited states of the above species are above 0.0002, which indicated that they could easily undergo photolysis in the sunlight. Therefore, they have received significant attention in the photochemistry of the brominated organic compounds produced by CH2@CHCH2Br + OH reaction, specifically their wave-length dependence.
4. Conclusions The potential energy surfaces (PES) for the CH2@CHCH2Br + OH reaction were systematically characterized at both the M06-2X and CCSD(T) levels. The calculated results revealed that the CH2@CHCH2Br + OH reaction takes place via the abstraction and addition/elimination mechanisms. The barrierless interaction of the two reactants leads to a pre-reactive complex, which bifurcates into two different pathways leads to two energy-rich adducts (IM1 and IM2) with excess energy, which can react further to decomposition or rearrangements. The variational transition state theory and the RRKM theory is employed to calculated the kinetics
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of the title reaction over the temperature range of 200–3000 K and the pressure range of 1014–1014 Torr. It is concluded that the stabilization of the adduct IM3 (CH2OHCHBrCH2) and P1 (CH2OH + CH2CHBr) dominate the reaction at 200–700 K and 700–1000 K, respectively. The rate constant shows a weak temperature dependence. The abstraction pathway from the ACH2Br group of CH2@CHCH2Br becomes dominant at higher temperatures. The rate constant shows a strong temperature dependence. Meanwhile, the total rate constant exhibits an obvious falloff behavior. Timedependent DFT (TD-DFT) calculations indicate that IM1-IM4, IM6, IM8 and IM9 take photolysis easily in the sunlight, once they are generated. Acknowledgments This work is supported by the National Natural Science Foundation of China (No. 21507027), the Youth Fund Project of HuBei Provincial Department of Education (Q20132501) and Hubei Key Laboratory of Pollutant Analysis & Reuse Technology Open Fund (PA160204). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.comptc.2017.01. 005. References [1] W.T. Tsai, Environmental risk assessment of hydrofluoroethers (HFEs), J. Hazard. Mater. 119 (2005) 69–78. [2] Scientific Assessment of ozone depletion, World Meteorological Organization. Report No. 25, Geneva, Switzerland, 1991. [3] J. Albaladejo, B. Ballesteros, E. Jimenez, Y. Diaz de Mera, E. Martinez, Gas-phase OH radical-initiated oxidation of the 3-halopropenes studied by PLP-LIF in the temperature range 228–388 K, Atmos. Environ. 37 (2003) 2919–2926. [4] J. Albaladejo, A. Notario, C.A. Cuevas, B. Ballesteros, E. Martinez, A pulsed laser photolysis-resonance fluorescence kinetic study of the atmospheric Cl atominitiated oxidation of propene and a series of 3-halopropenes at room temperature, J. Atmos. Chem. 45 (2003) 35–50. [5] R. Atkinson, S.M. Aschmann, M.A. Goodman, Kinetics of the gas-phase reactions of NO3 radicals with a series of alkynes, haloalkenes, and abunsaturated aldehydes, Int. J. Chem. Kinet. 19 (1987) 299–307. [6] Y. Gai, M. Ge, W. Wang, Kinetic studies of O3 reactions with 3-bromopropene and 3-iodopropene in the temperature range 288–328 K, Atmos. Environ. 43 (2009) 3467–3471.
[7] M.J. Frisch, G.W. Trucks, H.B. Schlegel, P.W.M. Gill, B.G. Johnson, M.A. Robb, J.R. Cheeseman, T.A. Keith, G.A. Petersson, J.A. Pople, et al., Gaussian 09, Gaussian Inc., Wallingford, CT, 2010. [8] Y. Zhao, D.G. Truhlar, The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functional, Theor. Chem. Account. 120 (2008) 215–241. [9] Y. Zhao, D.G. Truhlar, Density functionals with broad applicability in chemistry, Acc. Chem. Res. 41 (2008) 157–167. [10] C. Gonzalez, H. Bernhard Schlegel, An improved algorithm for reaction path following, J. Chem. Phys. 90 (1989) 2154–2161. [11] C. Gonzalez, H.B. Schlegel, An improved algorithm for reaction path following, J. Chem. Phys. 90 (1989) 2154–2161 (Reaction path following in massweighted internal coordinates. J. Phys.Chem. 94 (1990) 5523-5527). [12] K. Raghavachari, G.W. Trucks, J.A. Pople, M. Head-Gordon, A fifth-order perturbation comparison of electron correlation theories, Chem. Phys. Lett. 157 (1989) 479–483. [13] K.A. Holbrook, M.J. Pilling, S.H. Robertson, Unimolecular Reactions, Wiley, Chichester, UK, 1996. [14] H. Hou, B.S. Wang, Ab initio study of the reaction of propionyl (C2H5CO) radical with oxygen (O2), J. Chem. Phys. 127 (2007) 054306–054314. [15] H. Hou, B.S. Wang, Y.S. Gu, Ab initio mechanism and multichannel RRKMTST rate constant for the reaction of Cl(2P) with CH2CO (Ketene), J. Phys. Chem. A 104 (2000) 320. [16] Y.J. Zhang, K. Chao, J.Y. Sun, Z.M. Su, X.M. Pan, J.P. Zhang, R.S. Wang, Theoretical study on the gas phase reaction of allyl alcohol with hydroxyl radical, J. Phys. Chem. A 117 (2013) 6629–6640. [17] S.H. Mousavipour, S. Ramazani, Z. Shahkolahi, Multichannel RRKM-TST and direct-dynamics VTST study of the reaction of hydroxyl radical with furan, J. Phys. Chem. A 113 (2009) 2838–2846. [18] Y.J. Zhang, K. Chao, X.M. Pan, J.P. Zhang, Z.M. Su, R.S. Wang, Mechanism and kinetic study of 3-fluoropropene with hydroxyl radical reaction, J. Mol. Graph. Model. 48 (2014) 18–27. [19] J.Y. Sun, R.S. Wang, B.H. Wang, Theoretical study on the gas phase reaction of acrylonitrile with a hydroxyl radical, Phys. Chem. Chem. Phys. 13 (2011) 16585–16595. [20] NIST Computational Chemistry Comparison and Benchmark Database.