A DFT simulation on induction reactions involved radicals during pyrolysis of heavy organics
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摘要: 以重质有机资源热解过程中的自由基反应为背景,为了探究自由基对共价键的诱导作用及其对共价键解离能的影响,采用基于密度泛函理论的研究方法,选择ω
B97XD/6-31G**级别在Gaussian 09程序上对·CH3、·OH和·H分别诱导七类共价键反应过程的能量进行了理论计算。结果表明,空间位阻效应对自由基诱导反应能垒的影响占主要地位,共价键种类的影响相对次要;不存在·OH和·H的同基团诱导交换反应时,·OH诱导能垒比·H的高约40 kJ/mol,·CH3比·OH、·H的诱导能垒分别高约为50、90 kJ/mol;存在·OH或·H的同基团诱导交换反应时,会导致能垒约有70 kJ/mol的提高,在计算时应判断诱导反应的具体情况并加以修正。可以利用上述值估算不同共价键诱导反应的能垒。 -
关键词:
- 诱导反应 /
- 热解 /
- 自由基反应 /
- 密度泛函理论(DFT)
Abstract: With the free radical reaction during the pyrolysis process of heavy organics as the background, the research approach based on density functional theory was adopted to exploring the induction of free radicals on covalent bond and its effect on covalent bond dissociation energy. The energies of seven kinds of covalent bond reactions induced respectively by ·CH3, ·OH and ·H were calculated theoretically on the Gaussian 09 program at the level of ωB97XD/6-31G**. The results indicate that the steric hindrance effect plays a significant role in the energy barrier of free radical induced reaction, while the influence of the covalent bond type plays a minor role. When the isogroup induced exchange reaction of ·OH and ·H does not proceed, the induced energy barrier of ·OH is about 40 kJ/mol higher than that of ·H and the induced energy barrier of ·CH3 is about 50 and 90 kJ/mol higher than that of ·OH and ·H respectively. When the isogroup induced exchange reaction of ·OH and ·H works, it will result in the increasing of 70 kJ/mol of the energy barrier. During the process of calculation, the specific situation of induced reaction should be judged and revised. The above values can be used to estimate the energy barriers of different covalent bond induced reactions. -
Key words:
- induction reaction /
- pyrolysis /
- radical reaction /
- density functional theory (DFT)
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表 1 与自由基发生诱导反应的共价键
Table 1 The covalent bonds induced by free radicals
Cal−Cal Bond CH3-CH3 CH3-C2H5 CH3-CH2Ph CH3-CH2CH=CH2 CH3-CH2OH HOCH2-C2H5 HOCH2-CH2OH CH3-CH2OCH3 Cal−Car Bond C2H5-C2H3 CH3-Ph C2H5-Ph nC3H7-Ph HOCH2-Ph Cal−H Bond H-CH3 H-C2H5 H-CH2C2H5
(H-CH2-cyclopropane)
(cyclobutene)
(cyclopentane)
(cyclohexane)H-CH2OH H-CH2CH=CH2 Car−H Bond H-CH=CH2 H-CH=CHCH3 H-Ph H-C(OH)=CH2
(naphthalene-αH)
(naphthalene-βH)Cal−O Bond HO-CH3 HO-C2H5 HO-CH2C2H5 HO-CH2CH2OH HO-CH2Ph CH3-OCH3 C2H5-OC2H5 CH3-OC2H5 CH3-OPh C3H7-OC2H3 Car−O Bond HO-Ph C3H7O-C2H3 CH3O-Ph C2H5O-Ph O−H Bond H-OCH3 H-OC2H5 H-OCH2C2H5 H-OCH(CH3)2 H-OPh H-OCH2Ph H-OPhOH(p) H-OPhCH3(p) 表 2 ·CH3诱导七种共价键的能垒范围和Gibbs能变化
Table 2 Range of energy barrier and the change of delta G of seven covalent bonds induced by ·CH3
Bonds REB/(kJ·mol−1) RDG/(kJ·mol−1) Cal−Cal 277.7−320.1 (−64.7)−0.0 Cal−Car 322.7−351.3 34.4−59.5 Cal−H 108.7−149.5 (−80.4)−0.0 Car−H 123.7−146.1 10.7−38.2 Cal−O 220.6−296.8 133.9−0.0 Car−O 311.4−347.8 45.0−75.1 O−H 100.1−125.7 (−95.6)−11.8 表 3 ·OH诱导七种共价键的能垒范围和Gibbs能变化
Table 3 The range of energy barrier and the change of delta G of seven covalent bonds induced by ·OH
Bonds REB/(kJ·mol−1) RDG/(kJ·mol−1) Cal−Cal 227.8−264.2 (−88.3)−(−23.6) Cal−Car 270.8−295.2 (−7.6)−35.9 Cal−H 63.8−92.9 (−136.0)−(−55.5) Car−H 82.5−92.8 (−44.8)−(−17.4) Cal−O R−OH: 294.1−297.2
R1O−R2: 205.8−253.3ROH: 120.2−161.5
R1OR2: (−157.5)−(−65.1)Car−O 325.5−370.1 200.2−243.7 O−H 53.6−73.6 (−151.5)−(−67.3) 表 4 ·H诱导七种共价键的能垒范围和Gibbs能变化
Table 4 The range of energy barrier and the change of delta G of seven covalent bonds induced by ·H
Bonds REB/(kJ·mol−1) RDG/(kJ·mol−1) Cal−Cal 207.1−238.2 (−152.8)−(−88.1) Cal−Car 235.9−265.2 (−43.8)−(−28.6) Cal−H 84.2−107.3 (−95.6)−(−15.2) Car−H 110.6−125.2 (−4.5)−23.0 Cal−O 169.0−226.0 (−221.9)−(−104.9) Car−O 207.8−238.2 (−102.4)−(−44.8) O−H 82.5−105.9 (−142.8)−(−27.0) 表 5 共价键的键解离能及诱导反应能垒
Table 5 The BDEs and the energy barriers of the induction reaction
Types of the covalence BDEs/
(kJ·mol−1)Energy barriers/
(kJ·mol−1)Types of the covalence BDEs/
(kJ·mol−1)Energy barriers/
(kJ·mol−1)C−C Bond Cal−Cal − ·CH3 ·OH ·H H-Ph 472.2 144.4 90.9 124.3 CH3-CH3 377.4 302.7 260.1 219.2 naphthalene (αH) 469.4 146.1 92.8 125.2 CH3-C2H5 370.3 308.1 261.2 224.7 naphthalene (βH) 468.2 143.4 91.3 124.3 CH3-CH2OH 364.8 301.6 250.5 219.7 C−O Bond Cal−O HOCH2-C2H5 356.9 320.1 252.0 237.1 HO-CH3 384.9 268.6 297.2 180.5 HOCH2-CH2OH 358.2 316.2 227.8 238.2 HO-C2H5 391.2 268.1 290.3 182.2 CH3-CH2OCH3 363.2 277.7 253.9 207.1 HO-CH2C2H5 392.0 267.5 293.6 180.3 CH3-CH2C2H3 317.6 290.1 245.8 213.7 HO-CH2Ph 340.2 244.2 263.4 169.0 CH3-CH2Ph 319.7 293.7 250.1 216.7 Cal−O − ·CH3 ·OH ·H Cal−Car HO-CH2CH2OH 338.9 269.4 294.1 181.7 C2H5-C2H3 418.4 338.1 286.6 254.6 CH3-OCH3 349.8 276.2 253.3 205.8 CH3-Ph 426.8 322.7 284.5 235.9 CH3-OC2H5 348.1 274.8 249.3 204.9 C2H5-Ph 419.2 348.2 295.2 260.2 C2H5-OC2H5 355.6 296.8 259.1 226.0 nC3H7-Ph 421.7 351.3 293.7 261.8 CH3-OPh 268.6 233.0 205.8 173.8 HOCH2-Ph 413.4 342.3 270.8 265.2 C3H7-OC2H3 274.1 286.8 238.4 241.2 C−H Bond Cal−H Car−O H-CH3 439.3 125.6 70.7 102.8 HO-Ph 463.6 311.4 355.0 216.9 H-C2H5 420.5 122.1 66.8 93.6 C3H7O-C2H3 431.0 347.8 370.1 237.2 H−CH2C2H5 422.2 149.5 77.1 106.2 CH3O-Ph 416.7 315.5 325.1 207.8 H−CH2-
topcyclopropane407.5 137.4 85.5 107.3 C2H5O-Ph 416.7 316.6 337.6 209.4 cyclobutane 405.0 127.3 78.9 97.5 O−H Bond H-OCH3 437.7 110.3 72.1 105.1 cyclopentane 400.0 139.2 92.9 106.9 H-OC2H5 438.1 119.0 73.6 105.9 cyclohexane
(chair form)416.3 126.9 73.2 98.1 H-OCH2C2H5 432.6 117.8 72.8 104.1 H−CH2CH=CH2 369.0 108.7 63.8 84.2 H-OC(CH3)2 442.3 112.6 65.8 98.6 H−CH2OH 401.9 120.5 78.6 94.0 H-OCH2Ph 425.5 118.3 72.7 105.3 Car−H H-OCH=CH2 355.6 107.5 67.4 104.1 H−CH=CH2 465.3 140.3 87.6 117.4 H-OPh 368.2 125.7 67.9 104.3 H−C(CH3)=CH2 464.8 134.4 82.5 110.6 H-OPhCH3(p) 374.0 106.4 69.0 104.5 H−C(OH)=CH2 400.0 123.7 83.4 112.7 H-OPhOH(p) 352.0 100.1 64.5 95.6 -
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