Mechanism of the vinylcyclopropane-cyclopentene rearrangement studied by quasiclassical direct dynamics
Mechanism of the vinylcyclopropane-cyclopentene rearrangement studied by quasiclassical direct dynamics
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DOI：
10.1021/jp010464z
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发表时间：
2001-07-05
影响因子：
2.9
通讯作者：
Doubleday, C
中科院分区：
文献类型：
--
作者：
Doubleday, C
乙烯基环丙烷热重排为环戊烯的立体化学过程是使用准经典轨迹计算的，该轨迹在修改后的 AM1 势上运行，参数化以适合从头计算。在 573 K 时，34000 个轨迹通过 3 个过渡态 (TS) 结构的玻尔兹曼分布进行准经典初始化，三氘化总共 8 个非对映体 TS。计算出的产物比为 si:sr:ar:ai = 42:30:10:18 (exptl 40:23:13:24)，其中 s,a 指表面或反面烯丙基参与，r,i 指迁移亚甲基的保留或反转。每个 TS 的初始化都会导致所有 4 个产品，即产品分布完全处于动态控制之下。 400-1000 K 范围内产物比的温度依赖性很小。在 573 K 温度下，83% 的轨迹寿命低于 400 fs。对于时间 t ( 400 fs ，产物比强烈依赖于时间；对于 t > 400 fs ，产物比近似恒定并且更接近统计。然而，在 3 个 TS 结构处初始化的轨迹在任何情况下都不会给出相同的产物分布。扭转的均方根角速度在几乎整个反应过程中近似恒定。这些数据证明了非统计动力学，并且与涉及统计中间体的机制不一致。相反，该机制由 4 个相互竞争的直接反应组成。
The stereochemical course of the thermal rearrangement of vinylcyclopropane to cyclopentene is computed using quasiclassical trajectories run on a modified AM1 potential parametrized to fit ab initio calculations. At 573 K, 34000 trajectories are initialized quasiclassically with a Boltzmann distribution at 3 transition state (TS) structures, trideuterated for a total of 8 diastereomeric TSs. The computed product ratio is si:sr:ar:ai = 42:30:10:18 (exptl 40:23:13:24), where s,a refers to suprafacial or antarafacial allylic participation and r,i refers to retention or inversion of the migrating methylene. Initialization at each TS leads to all 4 products-that is, the product distribution is entirely under dynamical control. The temperature dependence of the product ratio over 400-1000 K is small. At 573 K, 83% of the trajectories have lifetimes under 400 fs. For times t ( 400 fs the product ratio is strongly time-dependent; for t > 400 fs the product ratio is approximately constant and closer to statistical. However, trajectories initialized at the 3 TS structures do not give identical product distributions under any circumstances. Root-mean-square angular velocities of the torsions are approximately constant over nearly the entire course of the reaction. These data demonstrate nonstatistical dynamics and are inconsistent with a mechanism involving a statistical intermediate. Instead, the mechanism consists of 4 competing direct reactions.