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Theoretical study on the mechanism for the reaction of OH with CH2CHCH2CH2OH
Chemical Physics 367 (2010) 52–61
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Theoretical study on the mechanism for the reaction of OH with CH2@CHCH2CH2OH Benni Du a,*, Changjun Feng b, Weichao Zhang a, Lailong Mu a a b
College of Chemistry and Chemical Engineering, Xuzhou Normal University, Xuzhou, Jiangsu 221116, People’s Republic of China College of Chemistry and Chemical Engineering, Xuzhou Institute of Technology, Xuzhou, Jiangsu 221008, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 4 August 2009 In final form 27 October 2009 Available online 29 October 2009 Keywords: CH2@CHCH2CH2OH OH Reaction mechanism QCISD(T)
a b s t r a c t The reaction mechanism of OH radicals with CH2@CHCH2CH2OH on the ground electronic state has been studied at the QCISD(T)/6-311++G(d,p) level of theory based on the geometric parameters optimized at the MP2(full)/6-311G(d,p) level of theory. Two types of reactions including the hydrogen abstraction and the addition–elimination reaction have been considered. The calculational results indicate that the formations of IM1(CH2(OH)CHCH2CH2OH) and IM2 (CH2CH(OH)CH2CH2OH) in the addition process via van der Waals complex PC3 will be more favorable than the abstraction reactions at room temperature. The formations of P20 (HCHO + CH3CH(OH)CH2) and P19 (CH3CHOH + CH(OH)@CH2) initiated from IM2 will be the most favorable reaction paths, whereas the hydrogen abstraction products of P6 (CH2@CHCH2CHOH(I)) + H2O via indirect mechanism and the dissociation products of P11 (CH2CH2CH2OH + HCHO) via TS7–P11 initiated from IM1 will be the minor ones. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction It is well known that the volatile organic compounds (VOCs) are emitted from various anthropogenic and biogenic sources (such as vegetation) and they play an important role in the troposphere [1–3]. Among the VOCs, the major classes of vegetative emission are alkenes and oxygenated VOCs including aldehydes, ketones, alcohols and ethers [4,5], and the unsaturated alcohols also have been found [6–8]. Hydroxyl radicals OH, NO3 and O3 are important oxidant agents in the atmosphere and the reactions of VOCs with the OH radicals are the dominant processes by which VOCs are removed during daytime. To date, numerous experimental and theoretical studies have been focused on the kinetics and mechanisms for the reactions of alkenes [9–14] and saturated alcohols [15–18]. However, only a few kinetic studies of the unsaturated alcohols with OH [19–24], NO3 [25,26] and O3 [27,28] are available in the literature. The rate coefficients and possible reaction mechanisms have been studied. Moreover, the atmospheric lifetime and fate of some unsaturated alcohols also have been estimated. The reactions of unsaturated alcohols with OH are considered as the major atmospheric loss process during daylight times and some attention has been paid to this system. In 1993, Grosjean et al. [19] studied the atmospheric oxidation of some unsaturated alcohols including allyl alcohol, 3-buten-1-ol and cis-3-hexen-1-ol with OH radicals under the conditions of unsaturated alcohol–nitric * Corresponding author. Fax: +86 516 83403164. E-mail address: [email protected] (B. Du). 0301-0104/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.chemphys.2009.10.022
oxide mixtures in the sunlight. They concluded that formaldehyde was the major carbonyl product for the OH-initiated oxidation of 3-buten-1-ol (CH2@CHCH2CH2OH). In 1995, Rudich et al. [20] investigated the fate of 2-methyl-3-buten-2-ol by measuring its UV absorption cross sections and gave the rate coefficient for its reaction with hydroxyl free radicals. In 2001, Papagni et al. [21] measured the rate constants for the gas-phase reactions of OH radicals with allyl alcohol, 3-buten-1-ol, 3-buten-2-ol and 2-methyl-3buten-2-ol using a relative rate method at 296 ± 2 K and atmospheric pressure of air. The rate constant for the title reaction of CH2@CHCH2CH2OH with OH is (5.50 ± 0.20) 10 11 cm3 molecule 1 s 1. The same method was used to study the reactions of OH radicals with three C5 biogenic alcohols [22]. Environmental chamber/FTIR apparatus [23] was used to study the rate coefficients and the products for the reactions of 1-penten-3-ol and (Z)-2-penten-1-ol with OH radicals at 298 K. Very recently, the rate coefficients for reactions of OH radicals with four unsaturated alcohols, including 3-methyl-3-buten-1-ol, 2-buten-1-ol, 2-methyl-2-propen-1-ol and 3-buten-1-ol, were investigated by Cometto et al. [24]. The conventional relative rate method and the pulsed laser photolysis-laser induced fluorescence technique were used to study these reactions over the temperature range 263–371 K and pressure of 100 Torr. The Arrhenius rate coefficients obtained by the above-mentioned two methods for the title reaction have been given. Negative temperature dependence of the rate constant has been derived for the addition mechanism of the OH radicals with CH2@CHCH2CH2OH. For the reactions of alkenes with OH, the major reaction pathway involves initial addition of the OH radicals to the carbon atoms of the C@C bond(s), and the H-atom abstraction reactions will be
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minor at room temperature and below [9]. For the reactions of saturated alcohols with OH radicals, the reactions proceed mainly by H-atom abstraction from the various C–H bonds [16]. The unsaturated alcohol CH2@CHCH2CH2OH possesses the characteristic of both an alkene and an alcohol. In order to know whether the addition–elimination or the H-atom abstraction reactions are important in the reaction of OH radicals with CH2@CHCH2CH2OH at room temperature, a theoretical study for the title reaction is essential. As far as we know, no corresponding quantum chemical investigations have been focused on the OH + CH2@CHCH2CH2OH system. In this paper, we present an extensive theoretical investigation for the title reaction. The main purpose of our study is to elucidate the reaction mechanism and give the possible product channels. 2. Computational methods The optimized geometries of the reactants, products, intermediates and transition states are calculated at the restricted and unrestricted second-order Møller–Plesset perturbation theory (MP2) [29] using the 6-311G(d,p) basis sets for closed shell and open shell, respectively. Harmonic vibrational frequencies are calculated at the same level to ensure the nature of the stationary points (minima or transition states) and to calculate the zero-point energy (ZPE). To confirm that the transition state really connects with designated intermediates along the reaction path, the intrinsic reaction coordinate (IRC) [30,31] calculations also have been done at the MP2(full)/6-311G(d,p) level. Furthermore, based on the MP2(full)/6-311G(d,p) geometries, single-point energies are refined with the quadratic configuration interaction method with single and double excitation and perturbative corrections for triple excitations (QCISD(T)) [32] with the 6-311++G(d,p) basis set. Unless otherwise specified, the QCISD(T) single-point energies with inclusion of MP2(full)/6-311G(d,p) ZPE are used in the following discussions. In addition, the T1 diagnostic [33,34] values of the corresponding stationary points also have been calculated to assess the reliability of these calculations. The T1 parameters of critical transition states and local minima were found to be small (<0.03) as presented in Table 1, showing that the wave function is dominated by a single configuration. The Gaussian 03 program packages [35] are employed to carry out all of the electronic structure calculations. 3. Results and discussion The geometries of the reactants, intermediates, transition states and products involved in the OH + CH2@CHCH2CH2OH reaction are shown in Figs. 1–3. As for the atom numbering, it is shown on the reactants in Fig. 1. The total energies, ZPE and relative energies (relative to reactants) of all species calculated at the QCISD(T)/6-311++G(d,p)//MP2(full)/6-311G(d,p) level of theory are summarized in Table 1. Finally, schematic energetic profiles of the potential energy surface (PES) for H-abstraction and addition–elimination branches obtained at the QCISD(T)/6311++G(d,p)//MP2(full)/6-311G(d,p) level are plotted in Figs. 4– 6, respectively. 3.1. Hydrogen-abstraction channels There are five different types of H atom in the reactant CH2@CHCH2CH2OH and the OH radicals can attack different H atoms to form H2O and other products. All of the transition state structures are shown in Fig. 1. Firstly, the OH radicals can abstract one of the H atoms in the end @CH2 group directly to form products of P1 (CH@CHCH2CH2
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OH(I)) + H2O (where the dot sign ‘‘” denotes the location of a radical center) or P2 (CH@CHCH2CH2OH(II)) + H2O via TS1 or TS2, respectively. The relative energies of TS1 and TS2 are 39.0 and 38.5 kJ/mol, respectively. P1 and P2 are a pair of isomers with the ‘‘HCCH” moiety staying trans-form and cis-form, respectively. Secondly, if it is the H atom in the @CH group that is abstracted, then P3 (CH2@CCH2CH2OH) + H2O will be formed via TS3 with a barrier height of 30.4 kJ/mol. Thirdly, the OH radicals can attack the H atoms in the middle and terminal –CH2 groups to form H2O and corresponding products. In these processes, the reactions begin with the barrierless formation of pre-reactive complexes (denoted as PCs) in the entrance channels. Two pre-reactive complexes PC1 and PC2 have been found between the reactant CH2@CHCH2CH2OH and OH radicals. This means that these reactions may proceed via an indirect mechanism. PC1 and PC2 lie 19.9 and 18.3 kJ/mol below the reactants, respectively, and they are characterized as true local minimum on the PES. In PC1, the O5–H9, O6–H4 and O6–H6 bond length are 1.884, 2.685 and 3.555 Å, respectively. The O5–H9, O6–H5 and O6–H7 bonds in PC2 are 1.879, 2.679 and 3.448 Å, respectively. The long O–H bonds in PC1 and PC2 illuminate that they are weak van der Waals complexes. The OH radicals can abstract the H4 and H5 atoms in the middle –CH2 group to form products of P4 (CH2@CHCHCH2OH(I)) + H2O and P5 (CH2@CHCH CH2OH(II)) + H2O via TS4 and TS5, which are initiated from PC1 and PC2, respectively. The relative energies of TS4 and TS5 are 11.7 and 8.6 kJ/mol, respectively. Starting form PC1 and PC2, the H6 and H7 atoms in the terminal –CH2 group may also be abstracted by OH radicals via TS6 and TS7 to form products of P6 (CH2@CHCH2CHOH(I)) + H2O and P7 (CH2@CHCH2CHOH(II)) + H2O, respectively. The barrier heights of TS6 and TS7 are 19.5 and 26.0 kJ/mol, respectively. TS6 lies 0.4 kJ/mol below the reactants and this indicates that the formation of P6 + H2O will be feasible for the title reaction. As shown in Fig. 1 and Table 1, P4 and P5 are a pair of enantiomorphs with same energies, whereas the products of P6 and P7 are a pair of isomers with different energies. Finally, the end H8 atom in –OH group may also be abstracted by OH radicals via TS8 to form corresponding products of P8 (CH2@CHCH2CH2O) + H2O, and this process is exothermic by 45.4 kJ/mol. TS8 lies 21.0 kJ/mol above the reactants. It can be seen from Fig. 4 that for these H-abstraction reactions, two types of reaction: direct and indirect abstraction via the formation of pre-reactive complexes have been found. For the direct hydrogen abstraction pathways, although the productions of P1 + H2O, P2 + H2O, P3 + H2O and P8 + H2O are exothermic by about 12–45 kJ/mol, the energies of the corresponding transition states are about 21–39 kJ/mol higher than that of the reactants. Thus these reaction pathways will be negligible at room temperature in the title reaction. For the indirect hydrogen abstraction reaction pathways, the energies of the transition states are slightly lower (TS6) or are only about 7–12 kJ/mol higher (TS4, TS5 and TS7) than that of the reactants, and the formations of P4 + H2O, P5 + H2O, P6 + H2O and P7 + H2O are exothermic by about 74–118 kJ/mol. Therefore, the formations of P4 + H2O, P5 + H2O, P6 + H2O and P7 + H2O will be more feasible thermodynamically and kinetically than that of P1 + H2O, P2 + H2O, P3 + H2O and P8 + H2O and the formation of P6 + H2O will be the major one in the hydrogen abstraction pathways. 3.2. 2 Addition–elimination pathways As can be seen from Figs. 2, 5 and 6, for the initial addition of OH radicals to the unsaturated C@C bond of CH2@CHCH2CH2OH, by analogy with other alkenes with OH radicals [10,12], the reaction proceeds via the formation of a pre-reaction van der Waals
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Table 1 T1 diagnostics, zero-point energies and relative energies for various species in the OH + CH2@CHCH2CH2OH reaction at the QCISD(T)/6-311G++(d,p)//MP2(full)/6-311G(d,p) level. Species
T1 diagnostics
ZPEa
OH + CH2@CHCH2CH2OH PC1 PC2 PC3 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 TSC3-1 TSC3-2 TS1-3 TS1-4 TS1-5 TS1-6 TS1-7 TS1–P12 TS3–P9 TS3–P10 TS4–P9 TS4–P11 TS5–P12 TS6–P10 TS7–P11 TS2-8 TS2-9 TS2-10 TS2-11 TS2-12 TS2–P10 TS8–P15 TS8–P16 TS9–P15 TS9–P17 TS10–P18 TS11–P19 TS12–P20 IM1 IM2 IM3 IM4 IM5 IM6 IM7 IM8 IM9 IM10 IM11 IM12 P1 ( CH@CHCH2CH2OH(I)) + H2O P2 (CH@CHCH2CH2OH(II)) + H2O P3 (CH2@CCH2CH2OH) + H2O P4 (CH2@CHCHCH2OH(I)) + H2O P5 (CH2@CHCHCH2OH(II)) + H2O P6 (CH2@CHCH2CHOH(I)) + H2O P7 (CH2@CHCH2CHOH(II)) + H2O P8 (CH2@CHCH2CH2O) + H2O H + C(O)HCH2CH2CH2OH (P9) CH(OH)@CH2 + CH2CH2OH (P10) CH2CH2CH2OH + HCHO (P11) CH2(OH)CH@CH2 + CH2OH (P12) CH2(OH)CH(T) + CH2CH2OH (P13) CH2OH + CHCH2CH2OH(T) (P14) H + CH3C(O)CH2CH2OH (P15) CH3C(OH)@CH2 + CH2OH (P16) CH3CHO + CH2CH2OH (P17) CH3 + CH(OH)@CHCH2OH (P18) CH3CHOH + CH(OH)@CH2 (P19) HCHO + CH3CH(OH)CH2 (P20) CH2(T) + CH(OH)CH2CH2OH (P21) CH2CH(OH)CH2(T) + CH2OH (P22)
0.0104, 0.0109 0.0111 0.0111 0.0110 0.0226 0.0227 0.0226 0.0227 0.0223 0.0218 0.0219 0.0287 0.0260 0.0263 0.0149 0.0172 0.0142 0.0168 0.0192 0.0244 0.0226 0.0242 0.0223 0.0213 0.0250 0.0243 0.0212 0.0157 0.0167 0.0148 0.0159 0.0185 0.0231 0.0219 0.0246 0.0220 0.0213 0.0240 0.0250 0.0211 0.0126 0.0125 0.0141 0.0373 0.0122 0.0139 0.0200 0.0143 0.0204 0.0125 0.0140 0.0154 0.0252, 0.0108 0.0250, 0.0108 0.0243, 0.0108 0.0235, 0.0108 0.0235, 0.0108 0.0159, 0.0108 0.0157, 0.0108 0.0319, 0.0108 0.0000, 0.0139 0.0136, 0.0120 0.0114, 0.0180 0.0115, 0.0173 0.0150, 0.0120 0.0173, 0.0124 0.0000, 0.0141 0.0122, 0.0173 0.0163, 0.0120 0.0080, 0.0130 0.0157, 0.0136 0.0180, 0.0118 0.0102, 0.0145 0.0137, 0.0173
0.123757 0.127227 0.127702 0.126023 0.123145 0.123389 0.123624 0.124450 0.124552 0.122588 0.125151 0.123568 0.127800 0.127639 0.125905 0.126877 0.126509 0.126299 0.127467 0.127806 0.122281 0.126904 0.122572 0.127176 0.127573 0.126635 0.127785 0.125342 0.126109 0.124593 0.125940 0.126305 0.126583 0.121897 0.126197 0.122846 0.126923 0.126107 0.126524 0.126898 0.130800 0.129530 0.131287 0.130681 0.129962 0.131312 0.130887 0.130637 0.131630 0.129004 0.130390 0.130133 0.124632 0.124438 0.124403 0.123228 0.123228 0.125909 0.125845 0.124096 0.119775 0.123195 0.122288 0.124867 0.120647 0.121619 0.119255 0.123535 0.122314 0.121461 0.124893 0.121675 0.119837 0.118767
a b
ZPE are in Hartree. Relative energies are in kJ/mol.
DE (QCISD(T) + ZPE)b 0.0 19.9 18.3 86.4 39.0 38.5 30.4 11.7 8.6 0.4 7.7 21.0 3.8 4.8 82.2 39.4 74.1 61.5 2.7 22.5 36.2 20.4 20.4 7.8 22.8 18.3 12.3 63.2 30.7 64.7 15.7 43.5 27.4 0.3 8.4 1.3 21.5 23.9 11.7 23.8 97.4 102.5 113.2 73.3 94.3 114.9 81.5 133.2 85.6 110.1 131.5 96.0 12.7 14.5 27.1 118.0 118.0 74.6 77.4 45.4 25.4 18.8 44.8 14.4 297.3 278.0 55.6 47.8 70.7 22.6 48.1 57.0 271.4 247.4
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Fig. 1. Optimized geometries for reactants, pre-reactive complexes, transition states and products involved in the hydrogen abstraction reaction pathways at the MP2(full)/6311G(d,p) level. Bond lengths are given in angstrom.
complex PC3 with the H atom of the OH radicals pointing toward the double bond. PC3 lies 6.4 kJ/mol below the reactants. Starting from PC3, the adducts IM1 (CH2(OH)CHCH2CH2OH) and IM2 (CH2CH(OH)CH2CH2OH) will be formed via transition states TSC3-1 and TSC3-2, respectively. TSC3-1 and TSC3-2 lie 3.8 and 4.8 kJ/mol below the original reactants and the barrier heights of them are 2.6 and 1.6 kJ/mol, respectively. IM1 lies 97.4 kJ/mol below the reactants and the heat of reaction can provide energy to make intermediate IM1 activated.
Starting from IM1, there are five possible isomerization pathways as follows: (i) it can isomerize to intermediate IM3 (CH(OH)CH2CH2CH2OH) by 1,2-H shift transition state TS1-3 with a barrier of 179.6 kJ/mol; (ii) it can undergo 1,3-H shift to IM4 (CH2(O)CH2CH2CH2OH) through transition state TS1-4 with a barrier of 136.8 kJ/mol; (iii) IM1 can rearrange to intermediate IM5 (CH2(OH)CH2CHCH2OH) by 1,2-H shift via a tight transition state TS1-5, which faces a barrier height of 171.5 kJ/mol; (iv) isomerization to IM6 (CH2(OH)CH2CH2CHOH) via four-membered ring tran-
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Fig. 2. Optimized geometries for pre-reactive complex, intermediates, transition states and products involved in the addition–elimination reaction of IM1 at the MP2(full)/6311G(d,p) level. Bond lengths are given in angstrom.
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Fig. 3. Optimized geometries for intermediates, transition states and products involved in the addition–elimination reaction of IM2 at the MP2(full)/6-311G(d,p) level. Bond lengths are given in angstrom.
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Fig. 4. Schematic potential energy surface for H-abstraction branches of the OH + CH2@CHCH2CH2OH reaction at the QCISD(T)/6-311++G(d,p)//MP2(full)/6-311G(d,p) level.
sition state TS1-6 overcoming a barrier height of 158.9 kJ/mol; and (v) rearrangement to IM7 (CH2(OH)CH2CH2CHO) by 1,4-H shift via five-membered ring transition state TS1-7 with a barrier of 100.1 kJ/mol. Three dissociation pathways of IM1 also have been found. Firstly, IM1 can decompose to products of P12 (CH2(OH)CH@ CH2 + CH2OH) by breaking the C3–C4 bond via TS1–P12, facing a barrier of 119.9 kJ/mol. Secondly, IM1 can dissociate into products
of P13 (CH2(OH)CH(T) + CH2CH2OH) and P14 (CHCH2CH2OH(T) + CH2OH) directly by C–C bond cleavage without exit barriers. P13 and P14 lie 297.3 and 278.0 kJ/mol above the reactants, respectively. The high energies of P13 and P14 exclude their importance in the title reaction. Among the eight reaction pathways starting from IM1, it is clearly seen that the isomerization to IM7 via five-membered ring transition state TS1-7 will be more favorable because of its lowest barrier.
Fig. 5. Schematic potential energy surface for addition–elimination branches of IM1 at the QCISD(T)/6-311++G(d,p)//MP2(full)/6-311G(d,p) level.
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Fig. 6. Schematic potential energy surface for addition–elimination branches of IM2 at the QCISD(T)/6-311++G(d,p)//MP2(full)/6-311G(d,p) level.
The intermediate, IM3, lying 113.2 kJ/mol below the reactants, can decompose to P9 (H + C(O)HCH2CH2CH2OH) via TS3–P9 by losing the H9 atom from O6 atom, or to P10 (CH(OH)@CH2 + CH2CH2OH) via TS3–P10 by C2–C3 bond cleavage. These pathways have barriers of 149.4 and 133.6 kJ/mol, respectively. The relative energy of IM4 is 73.3 kJ/mol. Two decomposition pathways of IM4 have been found. With one of the C1–H bonds cleavage, the products of P9 will be formed via TS4–P9, facing a barrier height of 93.7 kJ/mol. Another product pathway of IM4 is the formation of P11 (CH2CH2CH2OH + HCHO) via C1–C2 bond rupture transition state TS4–P11, which lies 7.8 kJ/mol below the reactants and 65.5 kJ/mol above the intermediate IM4. As shown in Fig. 5, the product pathway of P11 starting from IM4 has the lower barrier; however, the high isomerization barrier from IM1 to IM4 will make this pathway unimportant for the title reaction. IM5 and IM6 lie 94.3 and 114.9 kJ/mol below the reactants, respectively. The possible dissociation pathways of IM5 and IM6 are the formations of P12 and P10 via TS5–P12 and TS6–P10 with the barriers of 117.1 and 133.2 kJ/mol, respectively. IM7, lying 81.5 kJ/mol below the reactants, can easily dissociate to the products of P11 via TS7–P11 with a lower barrier of 69.2 kJ/ mol. The relative energy of TS7–P11 is 12.3 kJ/mol, and the isomerization transition state TS1-7 lies only 2.7 kJ/mol above the reactants, thus the formation of P11 via TS7–P11 will be the most favorable pathway of IM1. The energy of IM2 is 102.5 kJ/mol lower than that of the total energy of the original reactants. The high internal energy of IM2 drives it to promote various possible isomerization or dissociation reactions. Eight possible reaction pathways including five isomerization and three dissociation pathways have been found and they will be discussed in detail: (i) isomerization to intermediate IM8 (CH3C(OH)CH2CH2OH) via 1,2-H shift from C2 to C1. The corresponding transition state is TS2-8, which involves a high barrier height of 165.7 kJ/mol;
(ii) 1,3-H migration from O6 to C1 to form intermediate IM9 (CH3C(O)HCH2CH2OH), via transition state TS2-9 with a potential barrier of 133.2 kJ/mol; (iii) rearrangement to intermediate IM10 (CH3CH(OH)CHCH2OH) by 1,3-H shift from C3 to C1 via TS2-10, overcoming a high barrier of 167.2 kJ/mol; (iv) isomerization to IM11 (CH3CH(OH)CH2CHOH) via a five-membered ring transition state TS2-11 with a barrier of 86.8 kJ/mol; and finally, (v) rearrangement to intermediate IM12 (CH3CH(OH) CH2CH2O) by 1,5-H migration from O5 to C1 via a six-membered ring transition state TS2-12, which lies 43.5 kJ/mol below the reactants and has the lowest barrier of 59.0 kJ/mol starting from IM2. May be possessing lower strain energies for the larger size of the rings, it can be seen from Fig. 6 that the 1,4-H shift process of forming IM11 and 1,5-H shift process of forming IM12 involve lower barriers and thus are generally more competitive than the 1,3-H shift and 1,2-H shift steps. Three dissociation pathways of IM2 also have been investigated. The first dissociation pathway of IM2 is the formation of P10 (CH(OH)@CH2 + CH2CH2OH) via transition state TS2–P10 facing a barrier height of 129.9 kJ/mol. For the rest two dissociation channels, producing P21 (CH2(T) + CH(OH)CH2CH2OH) and P22 (CH2CH(OH)CH2(T) + CH2OH) initiated from IM2, no corresponding transition states have been found. The high energies of 271.4 and 247.4 kJ/mol for the products of P21 and P22 will prevent the two dissociation pathways to occur. From Fig. 6 and Table 1, it can be seen that intermediates IM8, IM9 and IM10 initiated from IM2 lie 133.2, 85.6 and 110.1 kJ/mol lower than that of the reactants and once they have been formed, a series of subsequent reaction pathways will be open. Two separate channels of IM8 have been taken into account. Firstly, IM8 can dissociate into the products P15 (CH3C(O)CH2CH2OH + H) by eliminating an H atom via TS8–P15 with a barrier of 133.5 kJ/ mol. Secondly, IM8 can dissociate into products P16 (CH3C(OH)@
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CH2 + CH2OH) by breaking the C3–C4 bond via TS8–P16, facing a barrier of 124.8 kJ/mol. Starting from IM9, there are two sub-channels to occur. With the ejection of the H atom in the –CHO moiety, the products of P15 will be formed via TS9–P15. TS9–P15 lies 1.3 kJ/mol below the reactants and the barrier height for this process is 84.3 kJ/ mol. The second reaction pathway of IM9 occurs through C2–C3 bond rupture, forming P17 (CH3CHO + CH2CH2OH) via transition state TS9–P17, which involves a barrier height of 64.1 kJ/mol. From the energy view, the transition states TS8–P15, TS8–P16, TS9–P15 and TS9–P17 are located near to or below the reactants on the PES, and the four series of product pathways starting from IM8 and IM9 will be feasible. However, the isomerization transition states TS2-8 and TS2-9 sit 63.2 and 30.7 kJ/mol above the reactants and the barrier heights of them are highly at 165.7 and 133.2 kJ/mol, respectively. Thus, the four product channels starting from IM8 and IM9 should have little contribution to the last product distribution. By eliminating a CH3 radical directly from IM10, the products of P18 (CH3 + CH(OH)@CHCH2OH) will be formed via TS10–P18 with a higher barrier of 134.0 kJ/mol. The energy of TS10–P18 is so high at 23.9 kJ/mol that this product pathway will be negligible. The lower-barrier isomerization intermediates IM11 and IM12, which lie 131.5 and 96.0 kJ/mol below the reactants, can dissociate into products of P19 (CH3CHOH + CH(OH)@CH2) and P20 (HCHO + CH3CH(OH)CH2) directly via TS11–P19 and TS12–P20, respectively. The relative energies of TS11–P19 and TS12–P20 are 11.7 and 23.8 kJ/mol and the barrier heights of them are 119.8 and 72.2 kJ/mol, respectively. As shown in Fig. 6, the formation of P20 initiated from IM2 is predicted to be the energetically most favorable reaction pathway because of the lowest barrier comparing with other reaction pathways of IM2. Comparing the H-abstraction reaction pathways with the addition–elimination reaction pathways, it can be seen that PC3 lies higher in energy than PC1 and PC2 at the entrance channel, however, TSC3-1 and TSC3-2 lie lower in energy than TS6 and the barriers of the TSC3-1 and TSC3-2 are lower than that of TS4, TS5, TS6 and TS7. This illuminates that the addition reactions will be more energetically favorable at low temperature, while the Habstraction reactions may play an important role at high temperature, and this result is similar to the reactions of most alkenes with OH radicals [9]. Moreover, the energies of TS2-11, TS2-12, TS11– P19 and TS12–P20 involved in the addition–elimination reaction of IM2 are about 15–44 kJ/mol lower than that of the reactants, while TS1-7, which has the lowest barrier involved in the isomerization and dissociation pathways of IM1, lies still 2.7 kJ/mol above the reactants. These results indicate that the formations of P20 and P19 initiated from IM2 will be the major reaction pathways for the title reaction. Whereas the formation of P6 + H2O via pre-reactive complex PC1 and the formation of P11 via TS7–P11 initiated from IM1 will be the secondary product channels. In the literature, Grosjean et al. [19] gave HCHO as the major product under the conditions of containing O2 and NO in the sunlight. Our calculations show that the products of P20 (HCHO + CH3CH(OH)CH2) will be the major reaction pathway in the reaction of OH + CH2@CHCH2CH2OH. This indicates that formation of HCHO will be dominant even in the absence of O2 and NO for the title reaction. As mentioned above, in the addition–elimination reaction, the van der Waals complex PC3 and the transition states TSC3-1 and TSC3-2 lie 6.4, 3.8 and 4.8 kJ/mol below the reactants, respectively, and the barriers overcoming the van der Waals well in the addition process are only 2.6 and 1.6 kJ/mol, respectively. Thus, the negative temperature dependence of the rate constant for the OH + CH2@CHCH2CH2OH addition reaction should be obtained. This phenomenon is also observed and described experimentally by Cometto et al. [24].
4. Conclusions In the present work, the mechanism of the complex multi-channel reactions of OH + CH2@CHCH2CH2OH is revealed theoretically for the first time. The potential energy surface of this title reaction has been mapped out using dual-level QCISD(T)/6-311++G(d,p)// MP2(full)/6-311G(d,p) level of theory with ZPE correction. As shown in the PES, the most feasible reaction pathways proceed via the formation of pre-reactive complex PC3 to form IM2 in the addition reaction, followed by easy conversion to IM11 and IM12. IM12 and IM11 can undergo the C–C bond rupture to form the primary products P20 and P19, respectively. Pathways to products of P4 + H2O, P5 + H2O, P6 + H2O and P7 + H2O via pre-reactive complexes PC1 and PC2, together with P11 via TS7–P11 initiated from IM1 will probably represent secondary contributions. The calculational results indicate that the rate constants for the addition pathways of the title reaction should show a negative dependence on temperature. Acknowledgement This work is supported by the Natural Science Foundation of Xuzhou Normal University (07XLB09). References [1] W.L. Chameides, R.W. Lindsay, J. Richardson, C.S. Kiang, Science 241 (1988) 1473. [2] D. Poppe, M. Wallasch, J. Zimmerman, J. Atmos. Chem. 16 (1993) 61. [3] F. Fehsenfeld, J. Calvert, R. Fall, P. Goldan, A.B. Guenther, C.N. Hewitt, B. Lamb, S. Liu, M. Trainer, H. Westberg, P. Zimmerman, Global Biogeochem. Cycles 6 (1992) 389. [4] A. Guenther, C.N. Hewitt, D. Erickson, R. Fall, C. Geron, T. Graedel, P. Harley, L. Klinger, M. Lerdau, W.A. Mckay, T. Pierce, B. Scholes, R. Steinbrecher, R. Tallamraju, J. Taylor, P. Zimmermann, J. Geophys. Res. 100 (1995) 8873. [5] A. Guenther, C. Geron, T. Pierce, B. Lamb, P. Harley, R. Fall, Atmos. Environ. 34 (2000) 2205. [6] V.A. Isidorov, I.G. Zenkevich, B.V. Ioffe, Atmos. Environ. 19 (1985) 1. [7] P.D. Goldan, W.C. Kuster, F.C. Fehsenfeld, Geophys. Res. Lett. 20 (1993) 1039. [8] G. König, M. Brunda, H. Puxbaum, C.N. Hewitt, S.C. Duckham, J. Rudolph, Atmos. Environ. 29 (1995) 861. [9] R. Atkinson, J. Phys. Chem. Ref. Data 26 (1997) 215. [10] A.B. Vakhtin, S. Lee, D.E. Heard, I.W.M. Smith, S.R. Leone, J. Phys. Chem. A 105 (2001) 7889. [11] E.E. Greenwald, S.W. North, Y. Georgievskii, S.J. Klippenstein, J. Phys. Chem. A 109 (2005) 6031. [12] E.E. Greenwald, S.W. North, Y. Georgievskii, S.J. Klippenstein, J. Phys. Chem. A 111 (2007) 5582. [13] L.K. Huynh, K. Barriger, A. Violi, J. Phys. Chem. A 112 (2008) 1436. [14] L.K. Huynh, H.R. Zhang, S. Zhang, E. Eddings, A. Sarofim, M.E. Law, P.R. Westmoreland, T.N. Truong, J. Phys. Chem. A 113 (2009) 177. [15] R. Atkinson, J. Phys. Chem. Ref. Data (Monograph 2) (1994) 1. [16] E.S.C. Kwok, R. Atkinson, Atmos. Environ. 29 (1995) 1685. [17] K. Azad, J.M. Andino, Int. J. Chem. Kinet. 31 (1999) 810. [18] S. Xu, M.C. Lin, Proc. Combust. Inst. 31 (2007) 159. [19] D. Grosjean, E. Grosjean, E.L. Williams II, Environ. Sci. Technol. 27 (1993) 2478. [20] Y. Rudich, R. Talukdar, J.B. Burkholder, A.R. Ravishankara, J. Phys. Chem. 99 (1995) 12188. [21] C. Papagni, J. Arey, R. Atkinson, Int. J. Chem. Kinet. 33 (2001) 142. [22] T. Imamura, Y. Iida, K. Obi, I. Nagatani, K. Nakagawa, I.P. Klotz, S. Hatakeyama, Int. J. Chem. Kinet. 36 (2004) 379. [23] J.J. Orlando, G.S. Tyndall, N. Ceazan, J. Phys. Chem. A 105 (2001) 3564. [24] P.M. Cometto, P.R. Dalmasso, R.A. Taccone, S.I. Lane, F. Oussar, V. Daële, A. Mellouki, G.L. Bras, J. Phys. Chem. A 112 (2008) 4444. [25] M. Hallquist, S. Langer, E. Ljungström, I. Wängberg, Int. J. Chem. Kinet. 28 (1996) 467. [26] J. Noda, G. Nyman, S. Langer, J. Phys. Chem. A 106 (2002) 945. [27] D. Grosjean, E. Grosjean, E.L. Williams II, Int. J. Chem. Kinet. 25 (1993) 783. [28] E. Grosjean, D. Grosjean, Int. J. Chem. Kinet. 26 (1994) 1185. [29] C. Møller, M.S. Plesset, Phys. Rev. 46 (1934) 618. [30] C. Gonzalez, H.B. Schlegel, J. Chem. Phys. 90 (1989) 2154. [31] C. Gonzalez, H.B. Schlegel, J. Phys. Chem. 94 (1990) 5523. [32] J.A. Pople, M. Head-Gordon, K. Raghavachari, J. Chem. Phys. 87 (1987) 5968. [33] T.J. Lee, P.R. Taylor, Int. J. Quant. Chem. Symp. 23 (1989) 199. [34] J.C. Rienstra-Kiracofe, W.D. Allen, H.F. Schaefer III, J. Phys. Chem. A 104 (2000) 9823. [35] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar,
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Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A. Pople, Gaussian 03, Revision B.01, Gaussian Inc., Pittsburgh, PA, 2003.
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Theoretical study on the mechanism for the reaction of OH with CH2@CHCH2CH2OH Benni Du a,*, Changjun Feng b, Weichao Zhang a, Lailong Mu a a b
College of Chemistry and Chemical Engineering, Xuzhou Normal University, Xuzhou, Jiangsu 221116, People’s Republic of China College of Chemistry and Chemical Engineering, Xuzhou Institute of Technology, Xuzhou, Jiangsu 221008, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 4 August 2009 In final form 27 October 2009 Available online 29 October 2009 Keywords: CH2@CHCH2CH2OH OH Reaction mechanism QCISD(T)
a b s t r a c t The reaction mechanism of OH radicals with CH2@CHCH2CH2OH on the ground electronic state has been studied at the QCISD(T)/6-311++G(d,p) level of theory based on the geometric parameters optimized at the MP2(full)/6-311G(d,p) level of theory. Two types of reactions including the hydrogen abstraction and the addition–elimination reaction have been considered. The calculational results indicate that the formations of IM1(CH2(OH)CHCH2CH2OH) and IM2 (CH2CH(OH)CH2CH2OH) in the addition process via van der Waals complex PC3 will be more favorable than the abstraction reactions at room temperature. The formations of P20 (HCHO + CH3CH(OH)CH2) and P19 (CH3CHOH + CH(OH)@CH2) initiated from IM2 will be the most favorable reaction paths, whereas the hydrogen abstraction products of P6 (CH2@CHCH2CHOH(I)) + H2O via indirect mechanism and the dissociation products of P11 (CH2CH2CH2OH + HCHO) via TS7–P11 initiated from IM1 will be the minor ones. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction It is well known that the volatile organic compounds (VOCs) are emitted from various anthropogenic and biogenic sources (such as vegetation) and they play an important role in the troposphere [1–3]. Among the VOCs, the major classes of vegetative emission are alkenes and oxygenated VOCs including aldehydes, ketones, alcohols and ethers [4,5], and the unsaturated alcohols also have been found [6–8]. Hydroxyl radicals OH, NO3 and O3 are important oxidant agents in the atmosphere and the reactions of VOCs with the OH radicals are the dominant processes by which VOCs are removed during daytime. To date, numerous experimental and theoretical studies have been focused on the kinetics and mechanisms for the reactions of alkenes [9–14] and saturated alcohols [15–18]. However, only a few kinetic studies of the unsaturated alcohols with OH [19–24], NO3 [25,26] and O3 [27,28] are available in the literature. The rate coefficients and possible reaction mechanisms have been studied. Moreover, the atmospheric lifetime and fate of some unsaturated alcohols also have been estimated. The reactions of unsaturated alcohols with OH are considered as the major atmospheric loss process during daylight times and some attention has been paid to this system. In 1993, Grosjean et al. [19] studied the atmospheric oxidation of some unsaturated alcohols including allyl alcohol, 3-buten-1-ol and cis-3-hexen-1-ol with OH radicals under the conditions of unsaturated alcohol–nitric * Corresponding author. Fax: +86 516 83403164. E-mail address: [email protected] (B. Du). 0301-0104/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.chemphys.2009.10.022
oxide mixtures in the sunlight. They concluded that formaldehyde was the major carbonyl product for the OH-initiated oxidation of 3-buten-1-ol (CH2@CHCH2CH2OH). In 1995, Rudich et al. [20] investigated the fate of 2-methyl-3-buten-2-ol by measuring its UV absorption cross sections and gave the rate coefficient for its reaction with hydroxyl free radicals. In 2001, Papagni et al. [21] measured the rate constants for the gas-phase reactions of OH radicals with allyl alcohol, 3-buten-1-ol, 3-buten-2-ol and 2-methyl-3buten-2-ol using a relative rate method at 296 ± 2 K and atmospheric pressure of air. The rate constant for the title reaction of CH2@CHCH2CH2OH with OH is (5.50 ± 0.20) 10 11 cm3 molecule 1 s 1. The same method was used to study the reactions of OH radicals with three C5 biogenic alcohols [22]. Environmental chamber/FTIR apparatus [23] was used to study the rate coefficients and the products for the reactions of 1-penten-3-ol and (Z)-2-penten-1-ol with OH radicals at 298 K. Very recently, the rate coefficients for reactions of OH radicals with four unsaturated alcohols, including 3-methyl-3-buten-1-ol, 2-buten-1-ol, 2-methyl-2-propen-1-ol and 3-buten-1-ol, were investigated by Cometto et al. [24]. The conventional relative rate method and the pulsed laser photolysis-laser induced fluorescence technique were used to study these reactions over the temperature range 263–371 K and pressure of 100 Torr. The Arrhenius rate coefficients obtained by the above-mentioned two methods for the title reaction have been given. Negative temperature dependence of the rate constant has been derived for the addition mechanism of the OH radicals with CH2@CHCH2CH2OH. For the reactions of alkenes with OH, the major reaction pathway involves initial addition of the OH radicals to the carbon atoms of the C@C bond(s), and the H-atom abstraction reactions will be
B. Du et al. / Chemical Physics 367 (2010) 52–61
minor at room temperature and below [9]. For the reactions of saturated alcohols with OH radicals, the reactions proceed mainly by H-atom abstraction from the various C–H bonds [16]. The unsaturated alcohol CH2@CHCH2CH2OH possesses the characteristic of both an alkene and an alcohol. In order to know whether the addition–elimination or the H-atom abstraction reactions are important in the reaction of OH radicals with CH2@CHCH2CH2OH at room temperature, a theoretical study for the title reaction is essential. As far as we know, no corresponding quantum chemical investigations have been focused on the OH + CH2@CHCH2CH2OH system. In this paper, we present an extensive theoretical investigation for the title reaction. The main purpose of our study is to elucidate the reaction mechanism and give the possible product channels. 2. Computational methods The optimized geometries of the reactants, products, intermediates and transition states are calculated at the restricted and unrestricted second-order Møller–Plesset perturbation theory (MP2) [29] using the 6-311G(d,p) basis sets for closed shell and open shell, respectively. Harmonic vibrational frequencies are calculated at the same level to ensure the nature of the stationary points (minima or transition states) and to calculate the zero-point energy (ZPE). To confirm that the transition state really connects with designated intermediates along the reaction path, the intrinsic reaction coordinate (IRC) [30,31] calculations also have been done at the MP2(full)/6-311G(d,p) level. Furthermore, based on the MP2(full)/6-311G(d,p) geometries, single-point energies are refined with the quadratic configuration interaction method with single and double excitation and perturbative corrections for triple excitations (QCISD(T)) [32] with the 6-311++G(d,p) basis set. Unless otherwise specified, the QCISD(T) single-point energies with inclusion of MP2(full)/6-311G(d,p) ZPE are used in the following discussions. In addition, the T1 diagnostic [33,34] values of the corresponding stationary points also have been calculated to assess the reliability of these calculations. The T1 parameters of critical transition states and local minima were found to be small (<0.03) as presented in Table 1, showing that the wave function is dominated by a single configuration. The Gaussian 03 program packages [35] are employed to carry out all of the electronic structure calculations. 3. Results and discussion The geometries of the reactants, intermediates, transition states and products involved in the OH + CH2@CHCH2CH2OH reaction are shown in Figs. 1–3. As for the atom numbering, it is shown on the reactants in Fig. 1. The total energies, ZPE and relative energies (relative to reactants) of all species calculated at the QCISD(T)/6-311++G(d,p)//MP2(full)/6-311G(d,p) level of theory are summarized in Table 1. Finally, schematic energetic profiles of the potential energy surface (PES) for H-abstraction and addition–elimination branches obtained at the QCISD(T)/6311++G(d,p)//MP2(full)/6-311G(d,p) level are plotted in Figs. 4– 6, respectively. 3.1. Hydrogen-abstraction channels There are five different types of H atom in the reactant CH2@CHCH2CH2OH and the OH radicals can attack different H atoms to form H2O and other products. All of the transition state structures are shown in Fig. 1. Firstly, the OH radicals can abstract one of the H atoms in the end @CH2 group directly to form products of P1 (CH@CHCH2CH2
53
OH(I)) + H2O (where the dot sign ‘‘” denotes the location of a radical center) or P2 (CH@CHCH2CH2OH(II)) + H2O via TS1 or TS2, respectively. The relative energies of TS1 and TS2 are 39.0 and 38.5 kJ/mol, respectively. P1 and P2 are a pair of isomers with the ‘‘HCCH” moiety staying trans-form and cis-form, respectively. Secondly, if it is the H atom in the @CH group that is abstracted, then P3 (CH2@CCH2CH2OH) + H2O will be formed via TS3 with a barrier height of 30.4 kJ/mol. Thirdly, the OH radicals can attack the H atoms in the middle and terminal –CH2 groups to form H2O and corresponding products. In these processes, the reactions begin with the barrierless formation of pre-reactive complexes (denoted as PCs) in the entrance channels. Two pre-reactive complexes PC1 and PC2 have been found between the reactant CH2@CHCH2CH2OH and OH radicals. This means that these reactions may proceed via an indirect mechanism. PC1 and PC2 lie 19.9 and 18.3 kJ/mol below the reactants, respectively, and they are characterized as true local minimum on the PES. In PC1, the O5–H9, O6–H4 and O6–H6 bond length are 1.884, 2.685 and 3.555 Å, respectively. The O5–H9, O6–H5 and O6–H7 bonds in PC2 are 1.879, 2.679 and 3.448 Å, respectively. The long O–H bonds in PC1 and PC2 illuminate that they are weak van der Waals complexes. The OH radicals can abstract the H4 and H5 atoms in the middle –CH2 group to form products of P4 (CH2@CHCHCH2OH(I)) + H2O and P5 (CH2@CHCH CH2OH(II)) + H2O via TS4 and TS5, which are initiated from PC1 and PC2, respectively. The relative energies of TS4 and TS5 are 11.7 and 8.6 kJ/mol, respectively. Starting form PC1 and PC2, the H6 and H7 atoms in the terminal –CH2 group may also be abstracted by OH radicals via TS6 and TS7 to form products of P6 (CH2@CHCH2CHOH(I)) + H2O and P7 (CH2@CHCH2CHOH(II)) + H2O, respectively. The barrier heights of TS6 and TS7 are 19.5 and 26.0 kJ/mol, respectively. TS6 lies 0.4 kJ/mol below the reactants and this indicates that the formation of P6 + H2O will be feasible for the title reaction. As shown in Fig. 1 and Table 1, P4 and P5 are a pair of enantiomorphs with same energies, whereas the products of P6 and P7 are a pair of isomers with different energies. Finally, the end H8 atom in –OH group may also be abstracted by OH radicals via TS8 to form corresponding products of P8 (CH2@CHCH2CH2O) + H2O, and this process is exothermic by 45.4 kJ/mol. TS8 lies 21.0 kJ/mol above the reactants. It can be seen from Fig. 4 that for these H-abstraction reactions, two types of reaction: direct and indirect abstraction via the formation of pre-reactive complexes have been found. For the direct hydrogen abstraction pathways, although the productions of P1 + H2O, P2 + H2O, P3 + H2O and P8 + H2O are exothermic by about 12–45 kJ/mol, the energies of the corresponding transition states are about 21–39 kJ/mol higher than that of the reactants. Thus these reaction pathways will be negligible at room temperature in the title reaction. For the indirect hydrogen abstraction reaction pathways, the energies of the transition states are slightly lower (TS6) or are only about 7–12 kJ/mol higher (TS4, TS5 and TS7) than that of the reactants, and the formations of P4 + H2O, P5 + H2O, P6 + H2O and P7 + H2O are exothermic by about 74–118 kJ/mol. Therefore, the formations of P4 + H2O, P5 + H2O, P6 + H2O and P7 + H2O will be more feasible thermodynamically and kinetically than that of P1 + H2O, P2 + H2O, P3 + H2O and P8 + H2O and the formation of P6 + H2O will be the major one in the hydrogen abstraction pathways. 3.2. 2 Addition–elimination pathways As can be seen from Figs. 2, 5 and 6, for the initial addition of OH radicals to the unsaturated C@C bond of CH2@CHCH2CH2OH, by analogy with other alkenes with OH radicals [10,12], the reaction proceeds via the formation of a pre-reaction van der Waals
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B. Du et al. / Chemical Physics 367 (2010) 52–61
Table 1 T1 diagnostics, zero-point energies and relative energies for various species in the OH + CH2@CHCH2CH2OH reaction at the QCISD(T)/6-311G++(d,p)//MP2(full)/6-311G(d,p) level. Species
T1 diagnostics
ZPEa
OH + CH2@CHCH2CH2OH PC1 PC2 PC3 TS1 TS2 TS3 TS4 TS5 TS6 TS7 TS8 TSC3-1 TSC3-2 TS1-3 TS1-4 TS1-5 TS1-6 TS1-7 TS1–P12 TS3–P9 TS3–P10 TS4–P9 TS4–P11 TS5–P12 TS6–P10 TS7–P11 TS2-8 TS2-9 TS2-10 TS2-11 TS2-12 TS2–P10 TS8–P15 TS8–P16 TS9–P15 TS9–P17 TS10–P18 TS11–P19 TS12–P20 IM1 IM2 IM3 IM4 IM5 IM6 IM7 IM8 IM9 IM10 IM11 IM12 P1 ( CH@CHCH2CH2OH(I)) + H2O P2 (CH@CHCH2CH2OH(II)) + H2O P3 (CH2@CCH2CH2OH) + H2O P4 (CH2@CHCHCH2OH(I)) + H2O P5 (CH2@CHCHCH2OH(II)) + H2O P6 (CH2@CHCH2CHOH(I)) + H2O P7 (CH2@CHCH2CHOH(II)) + H2O P8 (CH2@CHCH2CH2O) + H2O H + C(O)HCH2CH2CH2OH (P9) CH(OH)@CH2 + CH2CH2OH (P10) CH2CH2CH2OH + HCHO (P11) CH2(OH)CH@CH2 + CH2OH (P12) CH2(OH)CH(T) + CH2CH2OH (P13) CH2OH + CHCH2CH2OH(T) (P14) H + CH3C(O)CH2CH2OH (P15) CH3C(OH)@CH2 + CH2OH (P16) CH3CHO + CH2CH2OH (P17) CH3 + CH(OH)@CHCH2OH (P18) CH3CHOH + CH(OH)@CH2 (P19) HCHO + CH3CH(OH)CH2 (P20) CH2(T) + CH(OH)CH2CH2OH (P21) CH2CH(OH)CH2(T) + CH2OH (P22)
0.0104, 0.0109 0.0111 0.0111 0.0110 0.0226 0.0227 0.0226 0.0227 0.0223 0.0218 0.0219 0.0287 0.0260 0.0263 0.0149 0.0172 0.0142 0.0168 0.0192 0.0244 0.0226 0.0242 0.0223 0.0213 0.0250 0.0243 0.0212 0.0157 0.0167 0.0148 0.0159 0.0185 0.0231 0.0219 0.0246 0.0220 0.0213 0.0240 0.0250 0.0211 0.0126 0.0125 0.0141 0.0373 0.0122 0.0139 0.0200 0.0143 0.0204 0.0125 0.0140 0.0154 0.0252, 0.0108 0.0250, 0.0108 0.0243, 0.0108 0.0235, 0.0108 0.0235, 0.0108 0.0159, 0.0108 0.0157, 0.0108 0.0319, 0.0108 0.0000, 0.0139 0.0136, 0.0120 0.0114, 0.0180 0.0115, 0.0173 0.0150, 0.0120 0.0173, 0.0124 0.0000, 0.0141 0.0122, 0.0173 0.0163, 0.0120 0.0080, 0.0130 0.0157, 0.0136 0.0180, 0.0118 0.0102, 0.0145 0.0137, 0.0173
0.123757 0.127227 0.127702 0.126023 0.123145 0.123389 0.123624 0.124450 0.124552 0.122588 0.125151 0.123568 0.127800 0.127639 0.125905 0.126877 0.126509 0.126299 0.127467 0.127806 0.122281 0.126904 0.122572 0.127176 0.127573 0.126635 0.127785 0.125342 0.126109 0.124593 0.125940 0.126305 0.126583 0.121897 0.126197 0.122846 0.126923 0.126107 0.126524 0.126898 0.130800 0.129530 0.131287 0.130681 0.129962 0.131312 0.130887 0.130637 0.131630 0.129004 0.130390 0.130133 0.124632 0.124438 0.124403 0.123228 0.123228 0.125909 0.125845 0.124096 0.119775 0.123195 0.122288 0.124867 0.120647 0.121619 0.119255 0.123535 0.122314 0.121461 0.124893 0.121675 0.119837 0.118767
a b
ZPE are in Hartree. Relative energies are in kJ/mol.
DE (QCISD(T) + ZPE)b 0.0 19.9 18.3 86.4 39.0 38.5 30.4 11.7 8.6 0.4 7.7 21.0 3.8 4.8 82.2 39.4 74.1 61.5 2.7 22.5 36.2 20.4 20.4 7.8 22.8 18.3 12.3 63.2 30.7 64.7 15.7 43.5 27.4 0.3 8.4 1.3 21.5 23.9 11.7 23.8 97.4 102.5 113.2 73.3 94.3 114.9 81.5 133.2 85.6 110.1 131.5 96.0 12.7 14.5 27.1 118.0 118.0 74.6 77.4 45.4 25.4 18.8 44.8 14.4 297.3 278.0 55.6 47.8 70.7 22.6 48.1 57.0 271.4 247.4
B. Du et al. / Chemical Physics 367 (2010) 52–61
55
Fig. 1. Optimized geometries for reactants, pre-reactive complexes, transition states and products involved in the hydrogen abstraction reaction pathways at the MP2(full)/6311G(d,p) level. Bond lengths are given in angstrom.
complex PC3 with the H atom of the OH radicals pointing toward the double bond. PC3 lies 6.4 kJ/mol below the reactants. Starting from PC3, the adducts IM1 (CH2(OH)CHCH2CH2OH) and IM2 (CH2CH(OH)CH2CH2OH) will be formed via transition states TSC3-1 and TSC3-2, respectively. TSC3-1 and TSC3-2 lie 3.8 and 4.8 kJ/mol below the original reactants and the barrier heights of them are 2.6 and 1.6 kJ/mol, respectively. IM1 lies 97.4 kJ/mol below the reactants and the heat of reaction can provide energy to make intermediate IM1 activated.
Starting from IM1, there are five possible isomerization pathways as follows: (i) it can isomerize to intermediate IM3 (CH(OH)CH2CH2CH2OH) by 1,2-H shift transition state TS1-3 with a barrier of 179.6 kJ/mol; (ii) it can undergo 1,3-H shift to IM4 (CH2(O)CH2CH2CH2OH) through transition state TS1-4 with a barrier of 136.8 kJ/mol; (iii) IM1 can rearrange to intermediate IM5 (CH2(OH)CH2CHCH2OH) by 1,2-H shift via a tight transition state TS1-5, which faces a barrier height of 171.5 kJ/mol; (iv) isomerization to IM6 (CH2(OH)CH2CH2CHOH) via four-membered ring tran-
56
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Fig. 2. Optimized geometries for pre-reactive complex, intermediates, transition states and products involved in the addition–elimination reaction of IM1 at the MP2(full)/6311G(d,p) level. Bond lengths are given in angstrom.
B. Du et al. / Chemical Physics 367 (2010) 52–61
57
Fig. 3. Optimized geometries for intermediates, transition states and products involved in the addition–elimination reaction of IM2 at the MP2(full)/6-311G(d,p) level. Bond lengths are given in angstrom.
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Fig. 4. Schematic potential energy surface for H-abstraction branches of the OH + CH2@CHCH2CH2OH reaction at the QCISD(T)/6-311++G(d,p)//MP2(full)/6-311G(d,p) level.
sition state TS1-6 overcoming a barrier height of 158.9 kJ/mol; and (v) rearrangement to IM7 (CH2(OH)CH2CH2CHO) by 1,4-H shift via five-membered ring transition state TS1-7 with a barrier of 100.1 kJ/mol. Three dissociation pathways of IM1 also have been found. Firstly, IM1 can decompose to products of P12 (CH2(OH)CH@ CH2 + CH2OH) by breaking the C3–C4 bond via TS1–P12, facing a barrier of 119.9 kJ/mol. Secondly, IM1 can dissociate into products
of P13 (CH2(OH)CH(T) + CH2CH2OH) and P14 (CHCH2CH2OH(T) + CH2OH) directly by C–C bond cleavage without exit barriers. P13 and P14 lie 297.3 and 278.0 kJ/mol above the reactants, respectively. The high energies of P13 and P14 exclude their importance in the title reaction. Among the eight reaction pathways starting from IM1, it is clearly seen that the isomerization to IM7 via five-membered ring transition state TS1-7 will be more favorable because of its lowest barrier.
Fig. 5. Schematic potential energy surface for addition–elimination branches of IM1 at the QCISD(T)/6-311++G(d,p)//MP2(full)/6-311G(d,p) level.
B. Du et al. / Chemical Physics 367 (2010) 52–61
59
Fig. 6. Schematic potential energy surface for addition–elimination branches of IM2 at the QCISD(T)/6-311++G(d,p)//MP2(full)/6-311G(d,p) level.
The intermediate, IM3, lying 113.2 kJ/mol below the reactants, can decompose to P9 (H + C(O)HCH2CH2CH2OH) via TS3–P9 by losing the H9 atom from O6 atom, or to P10 (CH(OH)@CH2 + CH2CH2OH) via TS3–P10 by C2–C3 bond cleavage. These pathways have barriers of 149.4 and 133.6 kJ/mol, respectively. The relative energy of IM4 is 73.3 kJ/mol. Two decomposition pathways of IM4 have been found. With one of the C1–H bonds cleavage, the products of P9 will be formed via TS4–P9, facing a barrier height of 93.7 kJ/mol. Another product pathway of IM4 is the formation of P11 (CH2CH2CH2OH + HCHO) via C1–C2 bond rupture transition state TS4–P11, which lies 7.8 kJ/mol below the reactants and 65.5 kJ/mol above the intermediate IM4. As shown in Fig. 5, the product pathway of P11 starting from IM4 has the lower barrier; however, the high isomerization barrier from IM1 to IM4 will make this pathway unimportant for the title reaction. IM5 and IM6 lie 94.3 and 114.9 kJ/mol below the reactants, respectively. The possible dissociation pathways of IM5 and IM6 are the formations of P12 and P10 via TS5–P12 and TS6–P10 with the barriers of 117.1 and 133.2 kJ/mol, respectively. IM7, lying 81.5 kJ/mol below the reactants, can easily dissociate to the products of P11 via TS7–P11 with a lower barrier of 69.2 kJ/ mol. The relative energy of TS7–P11 is 12.3 kJ/mol, and the isomerization transition state TS1-7 lies only 2.7 kJ/mol above the reactants, thus the formation of P11 via TS7–P11 will be the most favorable pathway of IM1. The energy of IM2 is 102.5 kJ/mol lower than that of the total energy of the original reactants. The high internal energy of IM2 drives it to promote various possible isomerization or dissociation reactions. Eight possible reaction pathways including five isomerization and three dissociation pathways have been found and they will be discussed in detail: (i) isomerization to intermediate IM8 (CH3C(OH)CH2CH2OH) via 1,2-H shift from C2 to C1. The corresponding transition state is TS2-8, which involves a high barrier height of 165.7 kJ/mol;
(ii) 1,3-H migration from O6 to C1 to form intermediate IM9 (CH3C(O)HCH2CH2OH), via transition state TS2-9 with a potential barrier of 133.2 kJ/mol; (iii) rearrangement to intermediate IM10 (CH3CH(OH)CHCH2OH) by 1,3-H shift from C3 to C1 via TS2-10, overcoming a high barrier of 167.2 kJ/mol; (iv) isomerization to IM11 (CH3CH(OH)CH2CHOH) via a five-membered ring transition state TS2-11 with a barrier of 86.8 kJ/mol; and finally, (v) rearrangement to intermediate IM12 (CH3CH(OH) CH2CH2O) by 1,5-H migration from O5 to C1 via a six-membered ring transition state TS2-12, which lies 43.5 kJ/mol below the reactants and has the lowest barrier of 59.0 kJ/mol starting from IM2. May be possessing lower strain energies for the larger size of the rings, it can be seen from Fig. 6 that the 1,4-H shift process of forming IM11 and 1,5-H shift process of forming IM12 involve lower barriers and thus are generally more competitive than the 1,3-H shift and 1,2-H shift steps. Three dissociation pathways of IM2 also have been investigated. The first dissociation pathway of IM2 is the formation of P10 (CH(OH)@CH2 + CH2CH2OH) via transition state TS2–P10 facing a barrier height of 129.9 kJ/mol. For the rest two dissociation channels, producing P21 (CH2(T) + CH(OH)CH2CH2OH) and P22 (CH2CH(OH)CH2(T) + CH2OH) initiated from IM2, no corresponding transition states have been found. The high energies of 271.4 and 247.4 kJ/mol for the products of P21 and P22 will prevent the two dissociation pathways to occur. From Fig. 6 and Table 1, it can be seen that intermediates IM8, IM9 and IM10 initiated from IM2 lie 133.2, 85.6 and 110.1 kJ/mol lower than that of the reactants and once they have been formed, a series of subsequent reaction pathways will be open. Two separate channels of IM8 have been taken into account. Firstly, IM8 can dissociate into the products P15 (CH3C(O)CH2CH2OH + H) by eliminating an H atom via TS8–P15 with a barrier of 133.5 kJ/ mol. Secondly, IM8 can dissociate into products P16 (CH3C(OH)@
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CH2 + CH2OH) by breaking the C3–C4 bond via TS8–P16, facing a barrier of 124.8 kJ/mol. Starting from IM9, there are two sub-channels to occur. With the ejection of the H atom in the –CHO moiety, the products of P15 will be formed via TS9–P15. TS9–P15 lies 1.3 kJ/mol below the reactants and the barrier height for this process is 84.3 kJ/ mol. The second reaction pathway of IM9 occurs through C2–C3 bond rupture, forming P17 (CH3CHO + CH2CH2OH) via transition state TS9–P17, which involves a barrier height of 64.1 kJ/mol. From the energy view, the transition states TS8–P15, TS8–P16, TS9–P15 and TS9–P17 are located near to or below the reactants on the PES, and the four series of product pathways starting from IM8 and IM9 will be feasible. However, the isomerization transition states TS2-8 and TS2-9 sit 63.2 and 30.7 kJ/mol above the reactants and the barrier heights of them are highly at 165.7 and 133.2 kJ/mol, respectively. Thus, the four product channels starting from IM8 and IM9 should have little contribution to the last product distribution. By eliminating a CH3 radical directly from IM10, the products of P18 (CH3 + CH(OH)@CHCH2OH) will be formed via TS10–P18 with a higher barrier of 134.0 kJ/mol. The energy of TS10–P18 is so high at 23.9 kJ/mol that this product pathway will be negligible. The lower-barrier isomerization intermediates IM11 and IM12, which lie 131.5 and 96.0 kJ/mol below the reactants, can dissociate into products of P19 (CH3CHOH + CH(OH)@CH2) and P20 (HCHO + CH3CH(OH)CH2) directly via TS11–P19 and TS12–P20, respectively. The relative energies of TS11–P19 and TS12–P20 are 11.7 and 23.8 kJ/mol and the barrier heights of them are 119.8 and 72.2 kJ/mol, respectively. As shown in Fig. 6, the formation of P20 initiated from IM2 is predicted to be the energetically most favorable reaction pathway because of the lowest barrier comparing with other reaction pathways of IM2. Comparing the H-abstraction reaction pathways with the addition–elimination reaction pathways, it can be seen that PC3 lies higher in energy than PC1 and PC2 at the entrance channel, however, TSC3-1 and TSC3-2 lie lower in energy than TS6 and the barriers of the TSC3-1 and TSC3-2 are lower than that of TS4, TS5, TS6 and TS7. This illuminates that the addition reactions will be more energetically favorable at low temperature, while the Habstraction reactions may play an important role at high temperature, and this result is similar to the reactions of most alkenes with OH radicals [9]. Moreover, the energies of TS2-11, TS2-12, TS11– P19 and TS12–P20 involved in the addition–elimination reaction of IM2 are about 15–44 kJ/mol lower than that of the reactants, while TS1-7, which has the lowest barrier involved in the isomerization and dissociation pathways of IM1, lies still 2.7 kJ/mol above the reactants. These results indicate that the formations of P20 and P19 initiated from IM2 will be the major reaction pathways for the title reaction. Whereas the formation of P6 + H2O via pre-reactive complex PC1 and the formation of P11 via TS7–P11 initiated from IM1 will be the secondary product channels. In the literature, Grosjean et al. [19] gave HCHO as the major product under the conditions of containing O2 and NO in the sunlight. Our calculations show that the products of P20 (HCHO + CH3CH(OH)CH2) will be the major reaction pathway in the reaction of OH + CH2@CHCH2CH2OH. This indicates that formation of HCHO will be dominant even in the absence of O2 and NO for the title reaction. As mentioned above, in the addition–elimination reaction, the van der Waals complex PC3 and the transition states TSC3-1 and TSC3-2 lie 6.4, 3.8 and 4.8 kJ/mol below the reactants, respectively, and the barriers overcoming the van der Waals well in the addition process are only 2.6 and 1.6 kJ/mol, respectively. Thus, the negative temperature dependence of the rate constant for the OH + CH2@CHCH2CH2OH addition reaction should be obtained. This phenomenon is also observed and described experimentally by Cometto et al. [24].
4. Conclusions In the present work, the mechanism of the complex multi-channel reactions of OH + CH2@CHCH2CH2OH is revealed theoretically for the first time. The potential energy surface of this title reaction has been mapped out using dual-level QCISD(T)/6-311++G(d,p)// MP2(full)/6-311G(d,p) level of theory with ZPE correction. As shown in the PES, the most feasible reaction pathways proceed via the formation of pre-reactive complex PC3 to form IM2 in the addition reaction, followed by easy conversion to IM11 and IM12. IM12 and IM11 can undergo the C–C bond rupture to form the primary products P20 and P19, respectively. Pathways to products of P4 + H2O, P5 + H2O, P6 + H2O and P7 + H2O via pre-reactive complexes PC1 and PC2, together with P11 via TS7–P11 initiated from IM1 will probably represent secondary contributions. The calculational results indicate that the rate constants for the addition pathways of the title reaction should show a negative dependence on temperature. Acknowledgement This work is supported by the Natural Science Foundation of Xuzhou Normal University (07XLB09). References [1] W.L. Chameides, R.W. Lindsay, J. Richardson, C.S. Kiang, Science 241 (1988) 1473. [2] D. Poppe, M. Wallasch, J. Zimmerman, J. Atmos. Chem. 16 (1993) 61. [3] F. Fehsenfeld, J. Calvert, R. Fall, P. Goldan, A.B. Guenther, C.N. Hewitt, B. Lamb, S. Liu, M. Trainer, H. Westberg, P. Zimmerman, Global Biogeochem. Cycles 6 (1992) 389. [4] A. Guenther, C.N. Hewitt, D. Erickson, R. Fall, C. Geron, T. Graedel, P. Harley, L. Klinger, M. Lerdau, W.A. Mckay, T. Pierce, B. Scholes, R. Steinbrecher, R. Tallamraju, J. Taylor, P. Zimmermann, J. Geophys. Res. 100 (1995) 8873. [5] A. Guenther, C. Geron, T. Pierce, B. Lamb, P. Harley, R. Fall, Atmos. Environ. 34 (2000) 2205. [6] V.A. Isidorov, I.G. Zenkevich, B.V. Ioffe, Atmos. Environ. 19 (1985) 1. [7] P.D. Goldan, W.C. Kuster, F.C. Fehsenfeld, Geophys. Res. Lett. 20 (1993) 1039. [8] G. König, M. Brunda, H. Puxbaum, C.N. Hewitt, S.C. Duckham, J. Rudolph, Atmos. Environ. 29 (1995) 861. [9] R. Atkinson, J. Phys. Chem. Ref. Data 26 (1997) 215. [10] A.B. Vakhtin, S. Lee, D.E. Heard, I.W.M. Smith, S.R. Leone, J. Phys. Chem. A 105 (2001) 7889. [11] E.E. Greenwald, S.W. North, Y. Georgievskii, S.J. Klippenstein, J. Phys. Chem. A 109 (2005) 6031. [12] E.E. Greenwald, S.W. North, Y. Georgievskii, S.J. Klippenstein, J. Phys. Chem. A 111 (2007) 5582. [13] L.K. Huynh, K. Barriger, A. Violi, J. Phys. Chem. A 112 (2008) 1436. [14] L.K. Huynh, H.R. Zhang, S. Zhang, E. Eddings, A. Sarofim, M.E. Law, P.R. Westmoreland, T.N. Truong, J. Phys. Chem. A 113 (2009) 177. [15] R. Atkinson, J. Phys. Chem. Ref. Data (Monograph 2) (1994) 1. [16] E.S.C. Kwok, R. Atkinson, Atmos. Environ. 29 (1995) 1685. [17] K. Azad, J.M. Andino, Int. J. Chem. Kinet. 31 (1999) 810. [18] S. Xu, M.C. Lin, Proc. Combust. Inst. 31 (2007) 159. [19] D. Grosjean, E. Grosjean, E.L. Williams II, Environ. Sci. Technol. 27 (1993) 2478. [20] Y. Rudich, R. Talukdar, J.B. Burkholder, A.R. Ravishankara, J. Phys. Chem. 99 (1995) 12188. [21] C. Papagni, J. Arey, R. Atkinson, Int. J. Chem. Kinet. 33 (2001) 142. [22] T. Imamura, Y. Iida, K. Obi, I. Nagatani, K. Nakagawa, I.P. Klotz, S. Hatakeyama, Int. J. Chem. Kinet. 36 (2004) 379. [23] J.J. Orlando, G.S. Tyndall, N. Ceazan, J. Phys. Chem. A 105 (2001) 3564. [24] P.M. Cometto, P.R. Dalmasso, R.A. Taccone, S.I. Lane, F. Oussar, V. Daële, A. Mellouki, G.L. Bras, J. Phys. Chem. A 112 (2008) 4444. [25] M. Hallquist, S. Langer, E. Ljungström, I. Wängberg, Int. J. Chem. Kinet. 28 (1996) 467. [26] J. Noda, G. Nyman, S. Langer, J. Phys. Chem. A 106 (2002) 945. [27] D. Grosjean, E. Grosjean, E.L. Williams II, Int. J. Chem. Kinet. 25 (1993) 783. [28] E. Grosjean, D. Grosjean, Int. J. Chem. Kinet. 26 (1994) 1185. [29] C. Møller, M.S. Plesset, Phys. Rev. 46 (1934) 618. [30] C. Gonzalez, H.B. Schlegel, J. Chem. Phys. 90 (1989) 2154. [31] C. Gonzalez, H.B. Schlegel, J. Phys. Chem. 94 (1990) 5523. [32] J.A. Pople, M. Head-Gordon, K. Raghavachari, J. Chem. Phys. 87 (1987) 5968. [33] T.J. Lee, P.R. Taylor, Int. J. Quant. Chem. Symp. 23 (1989) 199. [34] J.C. Rienstra-Kiracofe, W.D. Allen, H.F. Schaefer III, J. Phys. Chem. A 104 (2000) 9823. [35] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar,
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