Theoretical study on the mechanism for the reaction of F with CH2CHCH2Cl

Computational and Theoretical Chemistry 981 (2012) 7–13

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Theoretical study on the mechanism for the reaction of F with CH2CHCH2Cl Yunju Zhang a, Jingyu Sun a, Kai Chao c, Fang Wang a, ShuWei Tang a, Xiumei Pan a, Jingping Zhang a, Hao Sun a,b,⇑, Rongshun Wang a,⇑ a

Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Renmin Road 5268, Changchun, Jilin 130024, PR China Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Changchun, Jilin 130023, PR China c Ningxia Entry-Exit Inspection and Quarantine Bureau, Yinchuan, Ningxia 750001, PR China b

a r t i c l e

i n f o

Article history: Received 2 July 2011 Received in revised form 7 November 2011 Accepted 7 November 2011 Available online 2 December 2011 Keywords: F CH2CHCH2Cl Reaction mechanism CCSD(T) MP2

a b s t r a c t The complex potential energy surfaces for the reaction of atomic radical F with CH2CHCH2Cl (3-chloropropene) are explored at the CCSD(T)/cc-pVTZ//MP2(full)/6-311++G(d,p) level. There are various possible reaction pathways including the addition–elimination and H-abstraction reaction. Among them, the most feasible pathway should be to produce P1 (CH2CHCH2F + Cl), which is in good agreement with the experiment. Among the H-abstraction reactions, the most competitive pathway is the atomic radical F abstracting hydrogen atom from allylic group. Because all of the transition states and intermediates involved in the title reaction lie below the reactants, the F + CH2CHCH2Cl reaction is expected to be rapid. The present results could lead us to deeply understand the mechanism of the title reaction and may provide some useful information for future experimental investigation of the title reaction. Ó 2011 Elsevier B.V. All rights reserved.

1. Introduction It is well known that the introduction of fluorine atom to the organic compounds can improve their thermal stability, oxidation resistance, electric effect and biological activity as well. Fluorinated organic compounds can be used as lubricant, refrigerator refrigerants, medicines and chemical textiles. However, preparation of fluorine-containing organic compounds is still a very challenging research field, because fluorine itself has high activity, and is difficult to control in the reaction. The introduction of fluorine atom in a particular position is more difficult. Selective introduction of fluorine atoms to the organic chemical industry is not only an important issue, but also the field of chemical research. There are many ways to accomplish the introduction of fluorine atom to organic compounds [1]. The introduction of fluorine atoms by the addition of F to the double bond is the most effective method. In this paper, the reaction of F + CH2CHCH2Cl is the fluorinated addition of carbon–carbon unsaturated bonds. The reactions of atomic radical F with halogenated alkenes were interest because of the complicated reaction mechanism. The reactions of fluorine atom with olefins have been studied both theoretically and experimentally [2–14]. Lee and his co-workers have ⇑ Corresponding authors. Address: Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Renmin Road 5268, Changchun, Jilin 130024, PR China (H. Sun). Tel./fax: +86 0431 85099511. E-mail addresses: [email protected] (H. Sun), [email protected] (R. Wang). 2210-271X/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.comptc.2011.11.010

performed a comprehensive study on the reactions of fluorine with many of olefins [2–5]. It was found that this class of reactions mainly proceeds by the addition of fluorine atoms to the double bond of olefins to form chemical activated radical complexes, which further decompose to unimolecules. Although there were a substantial of kinetic data for atomic radical F with a variety of alkenes, only limited information is available for halogenated alkenes. In 1985, Iyer [15] and his workers reported the overall reaction rate constant of (1.5 ± 0.4)  1010 cm3 molecule1 s1 for the reaction of F + CH2CHCH2Cl. Four possible reaction routes were presumed:

F þ CH2 CHCH2 Cl ! C3 H5 F þ Cl

ð1Þ

F þ CH2 CHCH2 Cl ! C2 H3 F þ CH2 Cl

ð2Þ

F þ CH2 CHCH2 Cl ! C3 H4 FCl þ H

ð3Þ

F þ CH2 CHCH2 Cl ! C3 H4 Cl þ HF

ð4Þ

They proposed that the title reaction proceeds via abstraction and addition, and the competition ability of the two types of reaction was 1:3. The relative rate of attacking the terminal/central carbon atoms in CH2CHCH2Cl are 1.55 ± 0.05 compared to 1.35 ± 0.02 for propene. There is no other theoretical study for mechanism and kinetics for the title reaction up to date. In view of the potential importance and the rather limited experimental and theoretical information, we carry out detailed theoretical study on the potential energy surfaces (PESs) of the F + CH2CHCH2Cl reaction to provide comprehensive insight into the reaction mechanism.

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2. Computational methods All the electronic structure calculations reported in this work were performed using the GAUSSIAN 03 program packages [16]. The geometries included in the F + CH2CHCH2Cl reaction were fully optimized using the unrestricted Møller–Plesset second-order perturbation MP2(full) [17] method with the 6-311++G(d,p) basis set. To check the influence of basis set, the correlation-consistent polarized valence triple-f basis sets cc-pVTZ was also employed with MP2 method to optimize the geometries of some important intermediates and transition states. There was a little change in comparison with the MP2(full)/6-311++G(d,p) geometrical parameters. It is indicated that the geometrical parameters are insensitive to the sizes of the basis sets. The harmonic vibrational frequencies were also calculated at the same level to characterize a minimum or a first-order transition state. The transition state connected between designated reactants and products have been confirmed by intrinsic reaction coordinate (IRC) calculations [18,19]. In order to obtain more reliable energies information, single-point energy calculations for the stationary points were carried out at the coupled-cluster (CCSD(T)) [20] method based on the MP2(full)/6-311++G(d,p) optimized geometries in conjunction with the correlation-consistent polarized valence triple-f basis sets cc-pVTZ [21]. For the purpose of obtaining an insight on multireference feature of the reaction pathways, the T1 diagnostic value was monitored for each stationary point using CCSD(T)/cc-pVTZ// MP2(full)/6-311++G(d,p). For closed-shell systems, the multireference wave function is significant if the T1 diagnostic values is greater than 0.02. A large number of studies have revealed that the values exceeding 0.045 are suspect for open-shell system [22–25]. Fortunately, the T1 diagnostic values of closed shell and open shell species involving in our system are smaller than 0.02

and 0.045, which implies the multireference character of wave functions is not an issue for the title reaction. The major problem in applying the unrestricted single-determinant reference wave functions is contamination with higher spin states. Severe spin contamination could lead to a deteriorated estimate of the barrier height [26,27]. We evaluate the spin contamination before and after annihilation for all species involved in the F + CH2CHCH2Cl reaction. Table S1 shows that the expectation values of hS2i for the doublet systems range from 0.751 to 0.984 before annihilation, whereas after annihilation hS2i is 0.75 (the precise value for a pure doublet is 0.75). It is indicated that the wave function is not severely contaminated by states of higher multiplicity.

3. Results and discussion There are enantiomorphs in the title reaction. For convenient and clear discussion, we only consider moieties of reaction channels which have some important enantiomorphous structures and enantiomorphic varieties. Fig. 1 depicts the optimized geometries of the reactants and products involved in the title reaction along with the available experimental values. It can be seen from Fig. 1 that the calculated bond lengths of product species are in good agreement with experimental values. The optimized geometries of intermediates and transition states are plotted in Fig. 2. The schematic potential energy surfaces (PESs) of the F + CH2CHCH2Cl reaction are presented in Figs. 3 and 4. Table 1 summarizes the ZPE corrections, T1 diagnostic value, relative energies, reaction enthalpies and Gibbs free energies. The harmonic vibrational frequencies of all species involved in the title reaction are summarized in Table S1 (in the supporting information). The frequencies

Fig. 1. The optimized structures of the reactants and products for the reaction of F with CH2CHCH2Cl. Numbers in roman type shown the structures at the MP2(full)/6311++G(d,p) level of theory. Numbers in italics shown the structures at the MP2(full)/6-311G level of theory. Numbers in bond are experimental date from Ref. [29]. Distances are given in angstroms and angles are in degrees.

Y. Zhang et al. / Computational and Theoretical Chemistry 981 (2012) 7–13

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Fig. 2. The optimized structures of intermediates and transition states for the reaction of F with CH2CHCH2Cl. Numbers in roman type show the structures at the MP2(full)/6311++G(d,p) level of theory. Numbers in italics show the structures at the MP2(full)/6-311G level of theory. Numbers in bond show the structures at the MP2(full)/cc-pVTZ level of theory. Distances are given in angstroms and angles are in degrees.

of CH2CHF, CH2CHCl and HF are in agreement with experimental data. For convenient discussion, the energy of R (F + CH2CHCH2Cl) is set as zero for reference. The symbol TSx–y is used to denote the transition state connecting the corresponding intermediates x and y. Unless otherwise specified, the geometric parameters and the energies used in the following discussion are at the CCSD(T)/ cc-pVTZ//MP2(full)/6-311++G(d,p) + ZPE level. 3.1. Initial association The ground-state atomic F adding to the C@C double bond of CH2CHCH2Cl leads to a pre-reactive complex I1

((CH2  F  CH)ringCH2Cl). I1 contains two CAF bonds (see Fig. 2), which is 12.24 kcal/mol more stable than the reactant. It is quit clear that this addition process is a barrier-free association. Consequently, complex I1 can undergo two concerted three-center F shifts; one of the F-shift is to the terminal unsaturated carbon atom via the transition state TS1–2 to produce the low-lying intermediate I2 (CH2FCHCH2Cl), while the other F-shift is to the central unsaturated carbon atom via the transition state TS1–3 by forming intermediate I3 (CH2CHFCH2Cl). The energy barrier heights of the I1 ? I2 and I1 ? I3 are 2.42 and 2.23 kcal/mol, respectively. A number of studies have shown that most radicals addition to the C@C double bond have negative activation barrier heights

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Y. Zhang et al. / Computational and Theoretical Chemistry 981 (2012) 7–13

Fig. 2 (continued)

0

R TS2-4 TS2-5 -4.11 -4.68

Δ E (kcal/mol)

-10

I1 -12.24

-20

TS2-P6 -9.46 TS1-3 TS1-2 -14.47 -14.66

-30

TS3-6-5.50 TS2-P7 TS2-P8 -7.05 TS3-P5 -7.54 -9.50 TS6-P4 P8 -12.54 P7-15.49 P6 -13.52 TS5-P3-16.14 P5 -17.36 TS3-P2 TS4-P2 -17.68 -18.20 P4 -18.55 P3 -23.50 P2 TS2-P1 -28.17 P1 -30.71 -32.64

-40

-50

I2 -48.60

-48.49 I3

-48.46 I4

-50.14 -52.06 I5 I6

Fig. 3. The profile of potential energy surface of the addition/elimination channels in the F + CH2CHCH2Cl reaction. The relative energies are calculated at the CCSD(T)/ccpVTZ//MP2(full)/6-311++G(d,p) level of theory.

[12–14]. I2 (CH2FCHCH2Cl) and I3 (CH2CHFCH2Cl) is 48.60 and 48.49 kcal/mol below the reactants, which means that the initial association provides I2 and I3 with enough energy to take subsequently changes.

Path 7 : R ! I1 ! I2 ! P7ðcis  CH2FCHCHCl þ HÞ Path 8 : R ! I1 ! I2 ! P8ðtrans  CH2FCHCHCl þ HÞ Path 9 : R ! I1 ! I2 ! I5 ! P3ðCH2 CHCl þ CH2 FÞ

3.2. Isomerization and elimination pathways The high internal energy of I2 and I3 drive them to promote various possible isomerization and elimination reactions. There are nine isomerization and dissociation pathways starting from I2 and I3 that can be written as:

Path 1 : R ! I1 ! I2 ! P1ðCH2 CHCH2 F þ ClÞ Path 2 : R ! I1 ! I3 ! P2ðCH2 CHF þ CH2 ClÞ Path 3 : R ! I1 ! I2 ! I4 ! P2 Path 4 : R ! I1 ! I3 ! I6 ! P4ðCH3 CFCHCl þ HÞ Path 5 : R ! I1 ! I3 ! P5ðCH2 CFCH2 Cl þ HÞ Path 6 : R ! I1 ! I2 ! P6ðCHFCHCH2 Cl þ HÞ

As can been seen from Fig. 3, there are many possible reaction pathways starting from I2 and I3. According to the small species in products, four different types channels have been found on the PES named as follows: (i) the Cl atom formation channel, that is, Path 1; (ii) the CH2Cl radical formation channels, Paths 2–3; (iii) the H-atom formation channels, Paths 4–8; and (iv) the CH2F radical formation channel, that is, Path 9. 3.2.1. The Cl-atom radical formation channel For I2 (CH2FCHCH2Cl), the direct CAC dissociation can lead to P1 (CH2CHCH2F + Cl) via TS2-P1. In the saddle point, TS2-P1, the length of the breaking CACl bond is 2.353 Å, which is 0.537 Å longer than the equilibrium bond lengths of CACl in isolated I2 (CH2FCHCH2Cl). The barrier height is 17.89 kcal/mol, and this channel is exothermic by 32.76 kcal/mol. The DG– for TS2-P1 is 23.26 kcal/mol, and the overall DG for this channel is 32.50 kcal/mol. Because all of the energies of all the stationary

Y. Zhang et al. / Computational and Theoretical Chemistry 981 (2012) 7–13

0

Δ E (kcal/mol)

-10

R

I9 -0.24 -2.56 I11-0.98 TS11-P13 -4.34 I8 I7 -4.82 TS7-P9 -5.86

I10 -0.56 TS10-P12 TS9-P11 -2.13 -2.80 TS8-P10 -5.50

-20 P11 -23.62

P13 -25.50

P12 -24.06

-30 P10 -35.88

-40

-50

P9 -52.82

Fig. 4. The profile of potential energy surface of the hydrogen abstraction channels in the F + CH2CHCH2Cl reaction. Numbers in roman type are relative energies at the CCSD(T)/cc-pVTZ//MP2(full)/6-311++G(d,p) + ZPE level of theory. Numbers in bond are relative energies at the CCSD(T)/cc-pVTZ//MP2(full)/6-311G + ZPE level of theory.

points in Path 1 are lower than the reactants, therefore the rate of this process should be very past.

11

Three H-atom formation pathways (from Path 6 to Path 8) have been found starting from intermediate I2 (CH2FCHCH2Cl). The energetically most favorable reaction path involves the formation of P6 (CHFCHCH2Cl + H) via TS2-P6 by CAH bond cleavage. The barrier height for this channel is calculated to be 39.14 kcal/mol at the CCSD(T)/cc-pVTZ level. I2 can also transform to P7 (cisCH2FCHCHCl + H) and P8 (trans-CH2FCHCHCl + H) via the CAH bond fission transition states TS2-P7 and TS2-P8 surmounting 41.55 and 41.06 kcal/mol, respectively. In view of the rate-determining reaction steps of the H-atom formation pathways, the ability of the reaction competition is Path 5, Path 6 > Path 8 > Path 7 > Path 4. 3.2.4. The CH2F radical formation channel In Path 9, a successive 1,2 H-shift and dissociation step can lead to product P3 (CH2CHCl + CH2F) via transition states TS2–5 and TS5-P3, respectively. The corresponding barrier heights are 43.92 and 34.00 kcal/mol. It should be pointed that the energy barrier is so high that this channel is expected to be negligible at low and moderate temperatures. 3.2.5. Hydrogen abstraction reaction mechanism As shown in Scheme 1, there are five different types of H atoms in CH2CHCH2Cl, namely as follows: the allylic H atom Ha and Hb; the vinyl inner H atom Hc; and the vinyl terminal H atom Hd and He. For convenient discussion, the five H(a–e)-abstraction pathways can be written as follows:

Path 10 : R ! I7 ! P9ðCH2 CHCHClðIÞ þ HFÞ Path 11 : R ! I8 ! P10ðCH2 CHCHClðIIÞ þ HFÞ

3.2.2. The CH2Cl radical formation channel For product P2 (CH2CHF + CH2Cl), there are two possible energetic pathways. The most feasible formation channel of I3 (CH2CHFCH2Cl) is the formation of P2 (CH2CHF + CH2Cl) via the CAC bond fission transition state TS3-P2 with a barrier of 30.81 kcal/mol as in Path 2. The second formation channel is I2 (CH2FCHCH2Cl) via successive 1,2-H shift and dissociation step (I2 ? I4 ? P2) to product P2 as in Path 3. Because of the ratedetermining barrier (44.49 kcal/mol) of Path 3 is higher than that of Path 2 (30.81), Path 3 should be far from competitive with Path 2 under normal conditions. It is worth noting that Iyer et al. do not distinguish whether the additional CH2CHF is formed by direct attacking by the atomic radical F on the C@C double bond, or by the formation of a much more highly excited radical in their experiment, or by both. In our present work, though an exhaustive search on the process of formation by direct attack by the atomic radical F on the C@C double bond, we cannot located this transition state. Therefore, we conjecture that the CH2CHF is formed by the formation of a much more highly excited radical. 3.2.3. The H-atom formation channel There are two H-atom formation channels (Path 4 and Path 5) starting from I3 (CH2CHFCH2Cl). In Path 4, I3 can isomerize to I6 (CH3CFCH2Cl) via a hydrogen migration transition structure (TS3–6) with a barrier of 42.99 kcal/mol. Subsequently, The CAH bond in I6 cleaves via a transition state TS6-P4 (12.54 kcal/ mol), and P4 (CH3CFCHCl + H) is generated. The relative energy of TS3–6 is 7.04 kcal/mol higher than that of TS6-P4. In Path 5, I3 (CH2CHFCH2Cl) can undergo H-elimination to product P5 (CH2CFCH2Cl + H) via TS3-P5 after overcoming a high barrier of 38.99 kcal/mol. It can be seen from Fig. 3 that the formation of I3 in Path 5 is similar with Path 2. The difference of the two pathways is how I3 (CH2CHFCH2Cl) transform to the corresponding products. Due to the higher barriers, the two channels are expected to be negligible.

Path 12 : R ! I9 ! P11ðCHCHCH2 ClðIÞ þ HFÞ Path 13 : R ! I10 ! P12ðCHCHCH2 ClðIIÞ þ HFÞ Path 14 : R ! I11 ! P13ðCH2 CCH2 Cl þ HFÞ It can be seen from Fig. 2 and Table 1, five pre-reactive loosely bound complexes (I7-I11) are located in the entrance of five hydrogen abstractions, and the barriers of the five processes are negative at the CCSD(T)//MP2 levels. In pathway Path 10, the corresponding transition state of abstracting a-allylic hydrogen (TS7-P9) stands 5.86 kcal/mol below the reactants. In the saddle point TS7-P9, the lengths of the breaking CAH bond and the newly formed HAF bond are 1.129 and 1.448 Å, respectively, which are 3.58% and 58.0% longer than the corresponding equilibrium bond lengths of CAH bond in CH2CHCH2Cl and HAF bond in HF. The elongation of the forming bond is longer than that of the breaking bond. Thus, TS7-P9 can be considered as an early transition state. As seen in Fig. 2 and Table 1, the character of the early or late transition states is in keeping with the perspective of Fisher and Radom [28] that an exothermic reaction corresponds to an early transition state while an endothermic reaction proceeds via a later transition state. Finally, P9 (CH2CHCHCl(I) + HF) is formed, and the reaction enthalpy (DH) and overall DG for this process are 51.72 kcal/mol and 53.30 kcal/mol, respectively, as well as the small barrier of this pathway is 1.04 kcal/mol, therefore, the formation of P9 (CH2CHCHCl(I) + HF) is both kinetically and thermodynamically favored. Similar to the Path 10, the F atom can abstract the b-allylic hydrogen via TS8-P10 with forming P10 (CH2CHCHCl(II) + HF) in the Path 11, The corresponding barrier is 1.16 kcal/mol, which is 0.12 kcal/mol higher than TS7-P9. In the TS8-P10 structure, the breaking CAH bond is 1.130 Å, stretched by 3.67%, compared to the reactant, and the forming HAF bond is 1.451 Å, 58.4% longer than the equilibrium bond length in HF. It is indicated that this

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Y. Zhang et al. / Computational and Theoretical Chemistry 981 (2012) 7–13

Table 1 ZPE corrections, T1 diagnostic values, relative energies, relative gibbs free energies and relative enthalpies for various species in the F + CH2CHCH2Cl reaction (the energies in kcal/mol).

a b c d e

Species

ZPE

T1b

DE c

DG d

R: CH2CHCH2Cl + F

45.41

0.00

I1 I2 I3 I4 I5 I6 I7 I8 I9 I10 I11 TS1–2 TS1–3 TS2–4 TS2–5 TS2-P1 TS2-P6 TS2-P7 TS2-P8 TS3–6 TS3-P2 TS3-P5 TS4-P2 TS5-P3 TS6-P4 TS7-P9 TS7-P9a TS8-P10 TS8-P10a TS9-P11a TS10-P12a TS11-P13a P1: CH2CHCH2F + Cl P2: CH2CHF + CH2Cl P3: CH2CHCl + CH2F P4: CH3CFCHCl + H P5: CH2CFCH2Cl + H P6: CHFCHCH2Cl + H P7: cis-CH2FCHCHCl + H P8: transCH2FCHCHCl + H P9: CH2CHCHCl(I) + HF P10: CH2CHCHCl(II) + HF P11: CHCHCH2Cl(I) + HF P12: CHCHCH2Cl(II) + HF P13: CH2CCH2Cl + HF

49.40 47.51 46.61 47.69 47.61 47.13 47.06 47.06 45.18 45.18 45.18 47.34 47.18 44.63 44.68 47.30 42.74 42.32 42.42 44.14 44.78 42.51 44.96 44.92 41.91 45.05 43.16 45.28 45.08 42.22 42.48 42.79 46.13 42.42 42.82 40.14 40.29 41.01 40.83 40.67

0.010, 0.005 0.015 0.012 0.011 0.012 0.013 0.012 0.026 0.024 0.027 0.027 0.027 0.021 0.020 0.014 0.014 0.023 0.023 0.024 0.024 0.014 0.025 0.024 0.025 0.025 0.024 0.026 0.025 0.024 0.027 0.026 0.027 0.027 0.010,0.000 0.012,0.014 0.010,0.014 0.011,0.000 0.011,0.000 0.011,0.000 0.011,0.000 0.011,0.000

12.24 48.60 48.49 48.46 50.14 52.06 4.82 4.34 0.24 0.56 0.98 14.66 14.47 4.11 4.68 30.71 9.46 7.05 7.54 5.50 17.68 9.50 18.20 16.14 12.54 5.86 5.57 5.50 3.12 2.13 2.80 2.56 32.64 28.17 23.50 18.55 17.36 15.32 15.49 14.10

4.62 41.16 40.84 41.01 42.74 44.68 0.26 0.70 3.18 3.36 2.61 7.00 6.70 3.24 2.68 23.26 1.96 0.05 0.16 2.29 10.63 1.47 11.50 9.55 4.80 0.60 0.46 1.16 3.44 1.06 0.65 0.77 32.50 31.79 26.88 16.88 15.69 13.91 14.32 12.52

13.16 49.30 49.14 49.30 50.92 52.72 4.74 4.26 0.48 0.58 1.24 15.68 15.50 4.90 5.53 31.61 10.28 7.76 8.28 6.34 18.24 10.49 18.70 16.60 13.20 6.29 6.46 6.04 4.16 5.63 6.42 6.16 32.76 27.78 23.27 15.04 16.96 14.93 15.04 13.62

42.62 44.84

0.026,0.006 0.018,0.006

52.28 35.88

53.30 37.08

51.72 35.33

42.72 42.68

0.029,0.007 0.029,0.007

23.62 24.06

25.06 25.44

23.04 23.50

42.56

0.029,0.007

25.50

27.05

23.50

0.00

Hc Ha

D He 0.00

The geometries obtained at the MP2(full)/6-311G + ZPE level. T1 diagnostic are calculated at the CCSD(T)/cc-pVTZ level. At the CCSD(T)/cc-pVTZ + ZPE level. The calculated Gibbs free energies at 298 K at the CCSD(T)/cc-pVTZ level. The calculated heats of reaction at 298 K at the CCSD(T)/cc-pVTZ level.

pathway also occurs via an early barrier, which is in accordance with the reaction exothermicity of 35.33 kcal/mol, which is 16.69 higher than that of Path 10. The hairelike difference of the two pathways may be proved that the abstraction of b-allylic hydrogen is competitive with that of a-allylic hydrogen appreciably. The F radical can abstract the vinyl hydrogen of CH2CHCH2Cl, which correspond to pathways Path 12, Path 13 and Path 14. It is worth noting that similar to the reaction of F + CH2CHCH3, though numerous attempts have been made, the three transition states TS9-P11, TS10-P12 and TS11-P13 are not located at MP2(full)/6311++G(d,p) and MP2(full)/6-311G(d,p). We employ MP2(full)/6311G to characterize these transition states. As shown in Table 1, at the CCSD(T)/cc-pVTZ// MP2(full)/6-311G level, the energies of

Hd Hb He Scheme 1. The five different chemical H atoms in CH2CHCH2Cl.

transition states and products, and energy barrier involving in Pathways Path 12–14 are higher than that of pathways Path 10 and Path 11. Therefore, from kinetic and thermodynamic consideration, it can be neglected the significance of the three H-abstraction pathways. It should be mentioned that we also reoptimized TS7-P9 and TS8-P10 at the MP2(full)/6-311G level. We compare the geometries obtained at the MP2(full)/6-311G level with those at the MP2(full)/6-311++G(d,p) level. It shows that the discrepancies are not large. For example, the lengths of the forming F. . .H bond in the two transition states obtained at the MP2(full)/6-311G level are about 0.13 Å shorter than that at the MP2(full)/6-311++G(d,p) level. Meanwhile, the lengths of the breaking C  H bond in them at a low level are 0.04 Å longer than that at a high level. Meanwhile, the transition state TS7-P9 and TS8-P10 are still lower than other three abstraction hydrogen transition states at the CCSD(T)/ cc-pVTZ//MP2(full)/6-311G level, which is consistent with the results obtained at the higher level. 3.3. Reaction mechanism and experimental implication From the above analyses, it is clearly that the atomic radical F can barrierlessly associate with 3-chloroproene (CH2CHCH2Cl) to form weakly bound complexes ((CH2  F  CH)ringCH2Cl), followed by F addition to the C@C double bond to form two low-lying isomers I2 and I3. Various isomerization and dissociation channels are probed starting from I2 (CH2FCHCH2Cl) and I3 (CH2CHFCH2Cl). However, only two pathways (Path 1 and Path 2) are the most probable. The most favorable pathway should be Path 1 because rate-determining transition state TS2-P1 (30.71 kcal/mol) in Path 1 lies much lower than TS3-P2 (17.68 kcal/mol) in Path 2. Moreover, P1 (32.64 kcal/mol) is more stable than P2 (28.17 kcal/mol). So the Path 2 may be significance at high temperatures. In the Habstraction pathways, we can find that the most competitive pathway should be the atomic radical F abstracting the allylic hydrogen. Other H-abstraction pathways are less favorable. Our computational results are in good agreement with the investigation by Iyer et al. in which the inspected major product is CH2CHCH2F + Cl that can be considered as one of the most feasible product CH2CHCH2F + Cl in our calculation. In Iyer’s experiment, four possible reaction routes were presumed: Cl + CH2CHCH2F, CH2Cl + CH2CHF, H + C3H4FCl and HF + C3H4Cl. They also considered that the formation of Cl is the most important channels for the title reaction, while the channels of formation of CH2Cl, H and HF are also significant. Furthermore, we also find another new possible product P3 (CH2CHCl + CH2F) (via Path 9), which may compete with P1 (CH2CHCH2F + Cl) and may play an important role at high temperatures. Finally, it should be noted that all stationary points involved in the title reaction are lower than that of the reactants. The rate of this reaction should be very fast. Once the addition reaction proceeds, the system should immediately enter a deep potential well.

Y. Zhang et al. / Computational and Theoretical Chemistry 981 (2012) 7–13

4. Conclusions A detailed potential energy surfaces for the reaction of F atomic radical with CH2CHCH2Cl are investigated at the MP2(full)/6311++G(d,p) and CCSD(T)/cc-pVTZ levels. Two different mechanisms and five reaction channels have been found in the present study. The Cl atom formation channel has lowest barrier and is most exothermic, and the rate-determining barrier is 17.89 kcal/mol. The channel of formation of CH2Cl radical which is initiated from I3 may be favorable than the other CH2Cl radical formation channel. The corresponding rate-determining barrier is 30.81 kcal/mol which is 12.92 kcal/mol higher than that of formation Cl atom. The CH2F radical formation channel and the H-atom formation channel may be favorable in high temperature ranges on the doublet PESs. While in H-abstraction reaction mechanism, the main pathway is abstracting the allylic H atoms. Our present work will be useful for understanding the mechanism of the F atomic reaction with halogenated alkenes reaction. Acknowledgments This work supported by the Postgraduate Innovation Fund sponsored by Northeast Normal University (No. 09SSXT121) is gratefully acknowledged. The authors are thankful for the reviewer’s invaluable comments.

Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.comptc.2011.11.010. Reference [1] J.A. Wilkinson, Recent advances in the selective formation of the carbonfluorine bond, Chem. Rev. 92 (1992) 505. [2] J.M. Parson, K. Shobatake, Y.T. Lee, S.A. Rice, Unimolecular decomposition of the long-lived complex formed in the reaction F + C4H8, J. Chem. Phys. 59 (1973) 1402–1415. [3] K. Shobatake, J.M. Parson, Y.T. Lee, S.A. Rice, Unimolecular decomposition of long-lived complexes of fluorine and substituted mono-olefins, cyclic olefins, and dienes, J. Chem. Phys. 59 (1973) 1416–1426. [4] J.M. Farrar, Y.T. Lee, The question of energy randomization in the decomposition of chemically activated C2H4F, J. Chem. Phys. 65 (1976) 1414–1426. [5] Q. Ran, C.H. Yang, Y.T. Lee, G. Shen, X. Yang, Dynamics of the F atom reaction with propene, J. Chem. Phys. 121 (2004) 6302–6308. [6] W.L. Hase, K.C. Bhalla, A classical trajectory study of the F + C2H4 ? C2H4F ? H + C2H3F reaction dynamics, J. Chem. Phys. 75 (1981) 2807–2819. [7] S. Kato, K. Morokuma, Potential energy characteristics and energy partitioning in chemical reactions: Ab Initio MO study of H2CCH2F ? H2CCHF + H reaction, J. Chem. Phys. 72 (1980) 206–217. [8] H.B. Schlegel, Ab initio molecular orbital studies of atomic hydrogen + ethylene and atomic fluorine + ethylene. 1. comparison of the equilibrium geometries, transition structures, and vibrational frequencies, J. Phys. Chem. 86 (1982) 4878–4882.

13

[9] H.B. Schlegel, K.C. Bhalla, W.L. Hase, Ab initio molecular orbital studies of atomic hydrogen + ethylene and atomic fluorine + ethylene. 2. comparison of the energetics, J. Phys. Chem. 86 (1982) 4883–4888. [10] G.N. Robinson, R.E. Continetti, Y.T. Lee, The translational energy dependence of the F + C2H4 ? H + C2H3F reaction cross section near threshold, J. Chem. Phys. 92 (1990) 275–284. [11] Q. Ran, C.H. Yang, Y.T. Lee, G. Shen, L. Wang, X. Yang, Molecular beam studies of the F atom reaction with Propyne: site specific reactivity, J. Chem. Phys. 122 (2005) 044307 (1-8). [12] M.B. Zhang, Z.Z. Yang, Computational study on the reaction CH2CH2 + F ? CH2CHF + H, J. Phys. Chem. A 109 (2005) 4816–4823. [13] J.L. Li, C.Y. Geng, X.R. Huang, C.C. Sun, A barrier-free atomic radical–molecule reaction: F + Propene, J. Chem. Theory. Comput. 2 (2006) 1551–1564. [14] P. Branã, J.A. Sordo, Theoretical approach to the mechanism of reactions between halogen atoms and unsaturated hydrocarbons: The Cl + propene reaction, J. Comput. Chem. 24 (2003) 2044–2062. [15] R.S. Iyer, L. Vasi, F.S. Rowland, Thermal fluorine atom reactions with 3chloropropene, J. Phys. Chem. 89 (1985) 55051. [16] 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, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. 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 03, Gaussian, Inc.: Wallingford CT, 2004. [17] H.B. Schlegel, Potential energy curves using unrestricted Møller–Plesset perturbation theory with spin annihilation, J. Chem. Phys. 84 (1986) 4530– 4534. [18] C. Gonzalez, H.B. Schlegel, An improved algorithm for reaction path following, J. Chem. Phys. 90 (1989) 2154. [19] C. Gonzalez, H.B. Schlegel, Reaction path following in mass-weighted internal coordinates, J. Phys. Chem. 94 (1990) 5523. [20] K. Raghavachari, G.W. Trucks, J.A. Pople, M. Head-Gordon, A fifith-order perturbation comparison of electron correlation theories, Chem. Phys. Lett. 157 (1989) 479. [21] T.H. Dunning, Jr, Gaussian basis sets for use in correlated molecular calculations I. The atoms boron through neon and hydrogen, J. Chem. Phys. 90 (1989) 1007–1023. [22] T.J. Lee, P.R. Taylor, A diagnostic for determining the quality of single-reference electron correlation methods, Int. J. Quantum. Chem. S23 (1989) 199. [23] J. Peiró-García, I. Nebot-Gil, Ab initio study on the mechanism of the atmospheric reaction OH + O3 ? HO2 + O2, Chem. Phys. Chem. 4 (2003) 843. [24] J. Peiró-García, I. Nebot-Gil, Ab initio study of the mechanism of the atmospheric reaction: NO2 + O3 ? NO3 + O2, J. Comput. Chem. 24 (2003) 1657. [25] J.C. Rienstra-Kiracofe, W.D. Allen, H.F. Schaefer III, The C2H5 + O2 reaction mechanism: high-level ab initio characterizations, J. Phys. Chem. A. 104 (2000) 9823. [26] I.S. Ignatyev, Y. Xie, W.D. Allen, H.F. Schaefer, Mechanism of the C2H5 + O2 reaction, J. Chem. Phys. 107 (1997) 141–155. [27] H.B. Schlegel, C. Sosa, Ab initio molecular orbital calculations on F + H2 ? HF + H and OH + H2 ? H2O + H using unrestricted Møller-Plesset Perturbation Theory with spin projection, Chem. Phys. Lett. 145 (1988) 329– 333. [28] H. Fisher, L. Radom, Was steuert die Additionen kohlenstoffzentrierter Radikale an Alkene-Antworten auf experimenteller und theoretischer Grundlage, Angew. Chem. 113 (2001) 1380; H. Fisher, L. Radom, Factors controlling the addition of carbon-centered radicals to alkenes – an experimental and theoretical perspective, Angew. Chem. Int. Ed. 40 (2001) 1340. [29] NIST Computational Chemistry Comparison and Benchmark Database. .