多环芳烃与不饱和自由基氢提取反应类的动力学研究

Rate Rules for Hydrogen Abstraction Reactions of Polycyclic Aromatic Hydrocarbons and Unsaturated Radicals

对2~6个环的多环芳烃的氢提取反应类进行了系统研究,提取氢原子的不饱和自由基包括丙炔基自由基(C_(3)H_(3))、烯丙基自由基(C_(3)H_(5))、丁二烯基自由基(nC_(4)H_(5),iC_(4)H_(5))、环戊二烯基自由基(C_(5)H_(5))以及苯基自由基(C_(6)H_(5)).采用M06-2X/cc-pVTZ方法得到了多环芳烃的电子结构信息,利用过渡态理论并结合Eckart隧道校正,计算了所有反应在500~2500 K范围内的反应速率常数.考察了多环芳烃的大小、结构对反应速率常数的影响,对比了不同氢提取自由基及不同氢提取反应类型的速率常数.结果表明,多环芳烃的大小对反应速率常数影响不大,但是多环芳烃的环结构对反应速率常数影响较大.将不同的氢提取反应类简化为发生在五元环上的C_(5)类和发生在六元环上的C_(6)类两类,结果表明,C_(6)类的反应活性高于C_(5)类.研究了nC_(4)H_(5),iC_(4)H_(5)以及C_(6)H_(5)自由基与多环芳烃的氢提取反应,它们的氢提取反应活性大小顺序为C_(6)H_(5)>nC_(4)H_(5)>iC_(4)H_(5).通过对每类典型反应的速率常数取平均值,总结出相应类型的速率规则,可用于构建多环芳烃和碳烟机理.

The reaction kinetics for a series of polycyclic aromatic hydrocarbons(PAHs)containing up to six aromatic rings by propynyl radical(C_(3)H_(3)),allyl radical(C_(3)H_(5)),butadienyl radical(nC_(4)H_(5),iC_(4)H_(5)),pentadienyl radical(C_(5)H_(5)) and phenyl radical(C_(6)H_(5)) were systematically investigated via the M06-2X/cc-pVTZ method.Based on the electronic structure calculations,the rate constants of title reactions were calculated by using transition state theory coupled with Eckart tunneling correction at the temperature range of 500-2500 K.The effects of PAH sizes and structures on the rate constants were examined.The results show that the PAH sizes have little effect on the rate constants,while the structures of PAHs influence the rate constant significantly.Hence,the hydrogen abstraction reactions are simplified into C_(5) and C_(6) reaction classes depending on the abstraction site on the five-membered or six-membered ring.The simple two classes are conducive to construct the combustion model of PAHs.The results indicate that C_(6) class possesses a higher activity than the C_(5) class.Hydrogen extraction reactions classes from PAHs by nC_(4)H_(5),iC_(4)H_(5) and C_(6)H_(5) radicals are studied in a systematic way,and the reactivity of different H-abstraction reactions from PAHs by different radicals shows the following trends:C_(6)H_(5)>nC_(4)H_(5)>iC_(4)H_(5).The rate rules are summarized by taking the average values of rate constants of a representative set of reactions in each class,which are applicable for the chemical model construction of PAHs.