在 [16] 中的动态过程:annulene Möbius 键转移路径改变配置
Ryan P Pemberton1, Colleen M McShane, Claire Castro
1Department of Chemistry, University of San Francisco, 2130 Fulton Street, San Francisco, CA 94117-1080, USA.
Journal of the American Chemical Society
|December 21, 2006
概括
计算方法揭示了[16]annulene改变其配置的低能途径. 这些动态过程涉及Möbius拓过渡状态,解释了 annulenes 中容易发生的热配置变化.
科学领域:
- * 理论化学 理论化学
- * 计算化学 计算机化学
- * 有机化学 有机化学
背景情况:
- * [16]annulene是一种已知的S4对称分子,具有动态过程.
- * 了解其结构自动化和配置变化至关重要.
研究的目的:
- * 调查[16]annulene中关键动态过程的机制.
- * 计算构造自动化和pi键转移的能量障碍.
- * 探索莫比乌斯拓在这些转换中的作用.
主要方法:
- *使用了密度函数理论 (DFT) 和ab initio方法.
- *使用BH&HLYP/6-311+G**和B3LYP/6-311+G**理论水平进行计算.
- * 高级合集群理论 [CCSD(T) /cc-pVDZ(est) ]用于验证.
主要成果:
- * 确定了两条逐步的结构自动化的途径,计算的能量障碍为8-10 kcal/mol.
- * 过渡状态表现出莫比乌斯拓,促进pi键转移和配置变化.
- * 关键过渡状态 (TS1-2) 能量在CCSD (T) 级别计算为13.7 kcal/mol,对实验数据进行括号化.
- * 其他几种莫比乌斯键移转过渡状态和构造最小值在基态22kcal/mol范围内被发现.
结论:
- *简单的热配置变化发生在[16]annulene中,通过涉及Möbius过渡状态的扭曲合键转移机制.
- * 这些机制与非循环多聚烯的机制形成鲜明对比,这些多聚烯通过单个二基过渡状态进行.
- *这项研究支持了莫比乌斯拓在 [4n] 无元的动态行为中起着关键作用的假设.
相关概念视频
Thermal Sigmatropic Reactions: Overview
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Sigmatropic shifts are classified based on an order term [i, j ], where i and j indicate the number of atoms across which each end of the σ bond migrates. Below are examples of a [3,3] sigmatropic shift in 1,5-hexadiene, referred to as...
Sigmatropic shifts are classified based on an order term [i, j ], where i and j indicate the number of atoms across which each end of the σ bond migrates. Below are examples of a [3,3] sigmatropic shift in 1,5-hexadiene, referred to as...
[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement
The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as annulenes. In...
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The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this staggered...
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