Seif Ahmad, Domingo Luis R, Zahedi Ehsan, Ahmadi Temer S, Mazarei Elham
Department of Chemistry, Central Tehran Branch, Islamic Azad University Tehran Iran
Department of Organic Chemistry, University of Valencia Dr. Moliner 50, 46100 Burjassot Valencia Spain.
RSC Adv. 2020 Sep 4;10(54):32730-32739. doi: 10.1039/d0ra05371f. eCollection 2020 Sep 1.
The kinetic and electron density flows are studied theoretically for the gas phase pyrolysis of cubane its cage opening to reach bicyclooctatriene and then thermal rearrangement of bicyclooctatriene to produce [8]annulene which is the experimentally observed major product. The observed kinetic data at the MN15-L/maug-cc-pVTZ level of theory were in good agreement with the experimental results as compared to the CBS-QB3 method. The cage opening and the thermal rearrangement steps at the experimentally employed temperature of 520 K were exergonic and exothermic. The atmospheric rate constants calculated by means of the RRKM theory show that the cage opening is the rate-determining step. The temperature dependence of the rate constant for the cage opening step at the MN15-L level can be expressed as log(/s) = (15.63) - (48.99 kcal mol)/ ln 10. The molecular mechanism of the reactions has been investigated by means of the bonding evolution theory (BET) at the B3LYP/6-311G (d,p) level of theory. The cage opening course is described topologically by cleaving of C1-C2, C4-C8, and C5-C6 single bonds and electron saturation of the C1-C4, C2-C6, and C5-C8 bonds, while the rearrangement of bicyclooctatriene is described by C3-C7 bond rupture, depopulation of C1-C4 and C5-C8 double bonds, and electron saturation of C1-C5, C3-C4, and C7-C8 bonds. Electron density rearrangement along the two successive steps are asynchronous and the sequence of catastrophes can be represented as: -1-13-CCFFFCCFFFCC-2-6-[C]C[F][C]C-0.
对立方烷的气相热解进行了理论上的动力学和电子密度流研究，其笼状结构打开生成双环辛三烯，然后双环辛三烯进行热重排生成[8]轮烯，这是实验观察到的主要产物。与CBS-QB3方法相比，在MN15-L/maug-cc-pVTZ理论水平下观察到的动力学数据与实验结果吻合良好。在实验采用的520 K温度下，笼状结构打开和热重排步骤都是放能和放热的。通过RRKM理论计算的常压速率常数表明，笼状结构打开是速率决定步骤。MN15-L水平下笼状结构打开步骤速率常数的温度依赖性可表示为log(k/s) = (15.63) - (48.99 kcal mol⁻¹)/ln 10。在B3LYP/6-311G(d,p)理论水平下，利用键演化理论(BET)研究了反应的分子机理。笼状结构打开过程通过C1-C2、C4-C8和C5-C6单键的断裂以及C1-C4、C2-C6和C5-C8键的电子饱和进行拓扑描述，而双环辛三烯的重排则通过C3-C7键的断裂、C1-C4和C5-C8双键的去填充以及C1-C5、C3-C4和C7-C8键的电子饱和进行描述。沿着这两个连续步骤的电子密度重排是异步的，灾变序列可表示为：-1-13-CCFFFCCFFFCC-2-6-[C]C[F][C]C-0。
