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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Kinetic and Thermodynamic Analysis on OH Addition to Ethylene: Adduct Formation, Isomerization, and Isomer Dissociations
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Kinetic and Thermodynamic Analysis on OH Addition to Ethylene: Adduct Formation, Isomerization, and Isomer Dissociations

机译：乙烯中OH加成反应的动力学和热力学分析：加合物形成，异构化和异构体离解

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摘要

Reaction pathways and kinetics are analyzed as function of temperature and pressure on formation and reactions of the adduct resulting from OH addition to ethylene. Ab initio methods are used to determine thermodynamic properties of intermediate radicals, transition states (TS) and vinyl alcohol. Enthalpies of formation (#DELTA#H_f deg_(298) in kcal/mol) are determined for C centre dot H_2CH_2OH, CH_3CH_2O~(centre dot), and CH_2CHOH using CBS-q//MP2(full)/6-31G(d,p) and G2 methods with isodesmic reactions, where zero point vibrational energies (ZPVE) and thermal correction to 298.15 K are incorporated. #DELTA#_f deg_(298) of TS's are determined for C centre dot H_2CH_2OH (H atom shift), CH_3CHO-H (#beta#-scission to form acetaldehyde + H), CH_3-CH_2O (#beta#-scission to form formaldehyde + methyl radical) and CH_2CHOH-H (#beta#-scission to form vinyl alcohol + H) using CBS-q//MP2(full)/6-31 G(d,p) and G2 methods. Entropies (S deg_(298) in cal/mol K) and heat capacities (C_p(T) 300 <= T/K <= 1500 in cal/mol K) are determined using geometric parameters and scaled vibrational frequencies obtained at the MP2(full)/6-31G(d,p) level of theory for CBS-q calculations. Geometric parameters obtained at MP2(full)/6-31G(d) level of theory and vibrational frequencies obtained at HF/6-31G(d) are used for G2 calculations. Quantum Rice-Ramsperger-Kassel (QRRK) analysis is used to calculate energy dependent rate constants, k(E), and master equation analysis is used to account for collisional stabilization. Rate constants are compared with experimentally determined product branching ratios (C centre dot H_2CH_2OH stabilization: CH_2O + CH_3:CH_3CHO + H). OH adds to ethylene to form an energized ethylene-OH adduct radical (C centre dot H_2CH_2OH)~*. This energized adduct can dissociate back to reactants, isomerize via hydrogen shift (E_(a,rxn) = 29.8 and 30.8 kcal/mol) to form CH_3CH_2O, (#DELTA#H_f deg_(298) = -1.7 and -3.3 kcal/mol) for CBS-q and G2 calculations respectively, or be stabilized. The CH_3CH_2O~(centre dot) isomer can undergo #beta#-scission reaction to either formaldehyde (CH_2O) + methyl radical (CH_3) (E_(a,rxn) = 13.4 and 16.0 kcal/mol) or acetaldehyde CH_3CHO + H atom (E_(a,rxn = 17.6 and 19.2 kcal/mol) for CBS-q and G2 calculations, respectively. Hydrogen atom tunneling is included by use of the Eckart formalism.Tunneling effect coefficients are 842, 93.1, and 21.1 for C centre dot H_2CH_2OH -> CH_3CH_2O, CH_3CH_2O~(centre dot) -> C centre dot H_2CH_2OH and CH_3CH_2O~(centre dot) -> CH_3CHO + H at 295 K, respectively. Chemical activation and falloff are determined to be of major importance in determination of the dominant reaction paths and rate constants versus pressure and temperature in this three heavy atom system.
机译：分析反应途径和动力学，作为温度和压力对形成和由OH加成至乙烯后生成的加合物的反应的函数。从头算方法用于确定中间自由基，过渡态（TS）和乙烯醇的热力学性质。使用CBS-q // MP2（full）/ 6-31G（d）确定C中心点H_2CH_2OH，CH_3CH_2O〜（中心点）和CH_2CHOH的形成焓（kcal / mol的＃DELTA＃H_f deg_（298）） ，p）和具有等离子反应的G2方法，其中结合了零点振动能量（ZPVE）和至298.15 K的热校正。确定TS的＃DELTA＃_f deg_（298）的C中心点H_2CH_2OH（H原子移位），CH_3CHO-H（＃beta＃-分裂形成乙醛+ H），CH_3-CH_2O（＃beta＃-分裂形成）使用CBS-q // MP2（full）/ 6-31 G（d，p）和G2方法测定CH_2CHOH-H（通过β-分解形成乙烯醇+ H）和CH_2CHOH-H。熵（cal / mol K中的S deg_（298））和热容（cal / mol K中的C_p（T）300 <= T / K <= 1500）使用MP2（完整）/ 6-31G（d，p）的CBS-q计算理论水平。在理论上的MP2（full）/ 6-31G（d）水平获得的几何参数和在HF / 6-31G（d）处获得的振动频率用于G2计算。量子莱斯-拉姆斯伯格-卡塞尔（QRRK）分析用于计算能量依赖的速率常数k（E），而主方程分析用于解决碰撞稳定问题。将速率常数与实验确定的产物支化比（C中心点H_2CH_2OH稳定度：CH_2O + CH_3：CH_3CHO + H）进行比较。 OH加到乙烯上形成一个加电的乙烯-OH加成基（C中心点H_2CH_2OH）〜*。这种激发的加合物可以解离成反应物，通过氢转移异构化（E_（a，rxn）= 29.8和30.8 kcal / mol）形成CH_3CH_2O（＃DELTA＃H_f deg_（298）= -1.7和-3.3 kcal / mol ）分别用于CBS-q和G2的计算，或者是稳定的。 CH_3CH_2O〜（中心点）异构体可以发生＃beta＃断裂反应，生成甲醛（CH_2O）+甲基（CH_3）（E_（a，rxn）= 13.4和16.0 kcal / mol）或乙醛CH_3CHO + H原子（ CBS-q和G2计算分别为E_（a，rxn = 17.6和19.2 kcal / mol），利用Eckart形式包括氢原子隧穿。C中心点H_2CH_2OH的隧穿效应系数分别为842、93.1和21.1。 -> CH_3CH_2O，CH_3CH_2O〜（中心点）-> C中心点H_2CH_2OH和CH_3CH_2O〜（中心点）-> CH_3CHO + H在295 K时确定化学活化和衰减对于确定显性在这三个重原子系统中，反应路径和速率常数与压力和温度的关系。

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