Department of Chemistry and Biochemistry, Florida International University, 11200 SW Eighth Street, Miami, Florida 33199, USA.
J Am Chem Soc. 2013 May 15;135(19):7251-63. doi: 10.1021/ja400227q. Epub 2013 May 1.
Ab initio G3(MP2,CC)/B3LYP/6-311G** calculations of potential energy surfaces (PESs) for the reactions of cyano and ethynyl radicals with styrene and N-methylenebenzenamine have been performed to investigate a possible formation mechanism of the prototype nitrogen-containing polycyclic aromatic compounds: (substituted) 1- and 2-azanaphthalenes. The computed PESs and molecular parameters have been used for RRKM and RRKM-Master Equation calculations of reaction rate constants and product branching ratios under single-collision conditions and at pressures from 3 to 10(-6) mbar and temperatures of 90-200 K relevant to the organic aerosol formation regions in the stratosphere of a Saturn's moon Titan. The results show that ethynyl-substituted 1- and 2-azanaphthalenes can be produced by consecutive CN and C2H additions to styrene or by two C2H additions to N-methylenebenzenamine. All CN and C2H radical addition complexes are formed in the entrance channels without barriers, and the reactions are computed to be exothermic, with all intermediates and transition states along the favorable pathways residing lower in energy than the respective initial reactants. The reactions are completed by dissociation of chemically activated radical intermediates via H losses, so that collisional stabilization of the intermediates is not required to form the final products. These features make the proposed mechanism viable even at very low temperatures and under single-collision conditions and especially significant for astrochemical environments. In Titan's stratosphere, collisional stabilization of the initial CN + styrene reaction adducts may be significant, but substantial amounts of 2-vinylbenzonitrile and 2-ethynyl-N-methylenebenzenamine can still be produced and then react with C2H to form substituted azanaphthalenes.
采用从头算 G3(MP2,CC)/B3LYP/6-311G**方法对氰基和乙炔基自由基与苯乙烯和 N-亚甲基苯甲胺反应的势能面（PESs）进行了计算，以研究含氮多环芳烃原型化合物（取代）1-和 2-氮萘的可能形成机制。计算得到的 PESs 和分子参数用于在 3 到 10(-6) mbar 压力和 90-200 K 温度范围内，对单分子碰撞条件下的反应速率常数和产物分支比进行 RRKM 和 RRKM-主方程计算，这些条件与土卫六（Saturn's moon Titan）平流层中有机气溶胶形成区域有关。结果表明，乙炔基取代的 1-和 2-氮萘可以通过苯乙烯上的连续 CN 和 C2H 添加或通过 N-亚甲基苯甲胺上的两个 C2H 添加生成。所有的 CN 和 C2H 自由基加成络合物都在入口通道中形成，没有势垒，反应被计算为放热反应，所有沿有利途径的中间体和过渡态的能量都低于相应的初始反应物。反应通过 H 损失使化学激活的自由基中间体解离完成，因此不需要中间体的碰撞稳定化来形成最终产物。这些特点使得即使在非常低的温度和单分子碰撞条件下，所提出的机制仍然可行，特别是对于天体化学环境而言。在土卫六的平流层中，初始 CN + 苯乙烯反应加合物的碰撞稳定化可能很重要，但仍可以大量生成 2-乙烯基苯甲腈和 2-乙炔基-N-亚甲基苯甲胺，然后与 C2H 反应形成取代的氮萘。
