Department of Chemistry and Biochemistry, Florida International University, 11200 SW 8th Street, Miami, Florida 33139, USA.
J Chem Phys. 2011 Jan 14;134(2):024302. doi: 10.1063/1.3526957.
Various mechanisms of the formation of naphthalene and its substituted derivatives have been investigated by ab initio G3(MP2,CC)∕B3LYP∕6-311G∗∗ calculations of potential energy surfaces for the reactions of one and two C(2)H additions to styrene combined with RRKM calculations of product branching ratios under single-collision conditions. The results show that for the C(2)H + styrene reaction, the dominant routes are H atom eliminations from the initial adducts; C(2)H addition to the vinyl side chain of styrene is predicted to produce trans or cis conformations of phenylvinylacetylene (t- and c-PVA), whereas C(2)H addition to the ortho carbon in the ring is expected to lead to the formation of o-ethynylstyrene. Although various reaction channels may lead to a second ring closure and the formation of naphthalene, they are not competitive with the direct H loss channels producing PVAs and ethynylstyrenes. However, c-PVA and o-ethynylstyrene may undergo a second addition of the ethynyl radical to ultimately produce substituted naphthalene derivatives. α- and β-additions of C(2)H to the side chain in c-PVA are calculated to form 2-ethynyl-naphthalene with branching ratios of about 30% and 96%, respectively; the major product in the case of α-addition would be cis-1-hexene-3,5-diynyl-benzene produced by an immediate H elimination from the initial adduct. C(2)H addition to the ethynyl side chain in o-ethynylstyrene is predicted to lead to the formation of 1-ethynyl-naphthalene as the dominant product. The C(2)H + styrene → t-PVA + H∕c-PVA + H∕ o-ethynylstyrene, C(2)H + c-PVA → 2-ethynyl-naphthalene + H, and C(2)H + o-ethynylstyrene → 1-ethynyl-naphthalene + H reactions are calculated to occur without a barrier and with high exothermicity, with all intermediates, transition states, and products lying significantly lower in energy than the initial reactants, and hence to be fast even at very low temperature conditions prevailing in Titan's atmosphere or in the interstellar medium. If styrene and C(2)H are available and overlap, the sequence of two C(2)H additions can result in the closure of a second aromatic ring and thus provide a viable route to the formation of 1- or 2-ethynyl-naphthalene. The analogous mechanism can be extrapolated to the low-temperature growth of polycyclic aromatic hydrocarbons (PAH) in general, as a step from a vinyl-PAH to an ethynyl-substituted PAH with an extra aromatic ring.
通过从头算 G3(MP2,CC)/B3LYP/6-311G∗∗ 对反应势能面的计算，并结合在单分子碰撞条件下 RRKM 对产物分支比的计算，研究了萘及其取代衍生物形成的各种机制。该反应涉及一个和两个 C(2)H 对苯乙烯的加成。结果表明，对于 C(2)H + 苯乙烯反应，主要途径是初始加合物中 H 原子的消除；预测 C(2)H 加成到苯乙烯的乙烯侧链会生成反式或顺式苯基乙烯基乙炔（t- 和 c-PVA），而 C(2)H 加成到环上的邻位碳预计会导致邻-乙炔基苯乙烯的形成。尽管各种反应途径可能导致第二个环闭合并形成萘，但它们与直接产生 PVAs 和乙炔基苯乙烯的 H 损失途径没有竞争力。然而，c-PVA 和 o-乙炔基苯乙烯可能会经历第二个乙炔基自由基的加成，最终产生取代的萘衍生物。通过计算，C(2)H 在 c-PVA 侧链上的α-和β-加成分别形成 2-乙炔基-萘，分支比约为 30%和 96%；在α-加成的情况下，主要产物是通过初始加合物中立即消除 H 形成的顺式 1-己烯-3,5-二炔基-苯。C(2)H 加成到 o-乙炔基苯乙烯的乙炔侧链预计会导致 1-乙炔基-萘的形成，这是主要产物。C(2)H + 苯乙烯→t-PVA + H/c-PVA + H/o-乙炔基苯乙烯、C(2)H + c-PVA→2-乙炔基-萘 + H 和 C(2)H + o-乙炔基苯乙烯→1-乙炔基-萘 + H 反应被计算为无势垒和高放热反应，所有中间体、过渡态和产物的能量明显低于初始反应物，因此即使在泰坦大气或星际介质中普遍存在的非常低的温度条件下也会很快发生。如果苯乙烯和 C(2)H 可用且重叠，则两个 C(2)H 加成的顺序可以导致第二个芳环的闭合，从而提供了形成 1-或 2-乙炔基-萘的可行途径。类似的机制可以推广到一般的多环芳烃（PAH）的低温生长，从乙烯基-PAH 到带有额外芳环的乙炔基取代 PAH 的一个步骤。
