Department of Mechanical Engineering, University of Illinois at Chicago, 842 West Taylor Street, Chicago, Illinois 60607, USA.
J Phys Chem A. 2011 Jun 9;115(22):5547-59. doi: 10.1021/jp200201c. Epub 2011 May 10.
The experimental investigations performed in the 1960s on the o-benzyne + benzene reaction as well as the more recent studies on reactions involving π-electrons highlight the importance of π-bonding for different combustion processes related to PAH's and soot formation. In the present investigation radical/π-bond addition reactions between single-ring aromatic compounds have been proposed and computationally investigated as possible pathways for the formation of two-ring fused compounds, such as naphthalene, which serve as precursors to soot formation. The computationally generated optimized structures for the stationary points were obtained with uB3LYP/6-311+G(d,p) calculations, while the energies of the optimized complexes were refined using the uCCSD(T) method and the cc-pVDZ basis set. The computations have addressed the relevance of a number of radical/π-bond addition reactions including the singlet benzene + o-benzyne reaction, which leads to formation of naphthalene and acetylene through fragmentation of the benzobicyclo[2,2,2]octatriene intermediate. For this reaction, the high-pressure limit rate constants for the individual elementary reactions involved in the overall process were evaluated using transition state theory analysis. Other radical/π-bond addition reactions studied were between benzene and triplet o-benzyne, between benzene and phenyl radical, and between phenyl radicals, for all of which potential energy surfaces were produced. On the basis of the results of these reaction studies, it was found necessary to propose and subsequently confirm additional, alternative pathways for the formation of the types of PAH compounds found in combustion systems. The potential energy surface for one reaction in particular, the phenyl + phenyl addition, is shown to contain a low-energy channel leading to formation of naphthalene that is energetically comparable to the other examined conventional pathways leading to formation of biphenyl compounds. This channel is the first evidence of a reaction which involves an aromatic radical adding to the nonradical π-bond site of another aromatic radical which leads directly to a fused ring structure.
20 世纪 60 年代对邻苯炔+苯反应的实验研究以及最近对涉及π 电子的反应的研究强调了π 键合对于与多环芳烃和烟尘形成有关的不同燃烧过程的重要性。在本研究中，提出并计算了单环芳烃之间的自由基/π 键加成反应，作为形成萘等双环稠合化合物的可能途径，这些化合物是烟尘形成的前体。用 uB3LYP/6-311+G(d,p)计算得到了固定点的计算生成优化结构，而用 uCCSD(T)方法和 cc-pVDZ 基组对优化复合物的能量进行了细化。计算涉及了许多自由基/π 键加成反应的相关性，包括导致苯并双环[2,2,2]辛三烯中间体断裂形成萘和乙炔的单重态苯+邻苯炔反应。对于这个反应，使用过渡态理论分析评估了整个过程中涉及的各个基元反应的高压极限速率常数。研究的其他自由基/π 键加成反应包括苯和三重态邻苯炔之间、苯和苯基自由基之间以及苯基自由基之间的反应，为所有这些反应都生成了势能面。根据这些反应研究的结果，发现有必要提出并随后确认形成燃烧系统中发现的多环芳烃化合物的替代途径。特别是苯基+苯基加成反应的势能面显示出一个低能通道，导致萘的形成，这与形成联苯化合物的其他被检验的常规途径具有可比性。这是第一个涉及芳香族自由基加成到另一个芳香族自由基的非自由基π键位置的反应的证据，该反应直接导致稠合环结构。
