压力催化键解离在一个Anthracene旋风光聚合物中的解离
Sebastian R Jezowski1, Lingyan Zhu, Yaobing Wang
1Department of Chemistry, University of California, Riverside, California 92521, USA.
Journal of the American Chemical Society
|April 11, 2012
概括
施加轻度压力可以通过显著降低激活能来加速二甲烯光二聚合物的解离. 这种压力诱导的键断裂为应力激活材料提供了新的途径.
科学领域:
- 摄影化学的使用.
- 材料科学 材料科学 材料科学
- 物理化学 物理化学
背景情况:
- 乙二甲烯 (BA) 经过 [4 + 4] 光环添加,形成一个光聚物.
- 这种光二聚含有两个循环butan环,其解离涉及打破两个碳-碳键.
研究的目的:
- 为了研究压力对二-二烯光二聚物的解离动力学的影响.
- 为了阐明压力加速共价键断裂的机制.
主要方法:
- 在Zeonex聚合物矩阵中研究了二元解离的反应动力学.
- 在各种压力 (高达0.9 GPa) 和温度下测量运动学.
- 分析了反应速率和激活量.
主要成果:
- 观察到的比特指数动力学,表明有两个bis-anthracene同位素.
- 解离速率强烈依赖压力,具有负激活体积 (ΔV(++) = -16 Å3).
- 在0.9GPa时,激活能量从93降至7kJ/mol.
结论:
- 压缩力可以催化分子中的共价键断裂.
- 更高的压力稳定了二聚体解离的过渡状态.
- 提出了一种两步机制,包括在键断裂之前使环平坦化.
相关概念视频
Mass Spectrometry: Cycloalkene Fragmentation
The molecular ions of cycloalkenes undergo fragmentation via a retro-Diels–Alder reaction.
Cycloaddition Reactions: MO Requirements for Photochemical Activation
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene molecules occurs only in the presence of light. It is photochemically allowed but thermally forbidden.
Photochemical Electrocyclic Reactions: Stereochemistry
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
Aromatic Hydrocarbon Cations: Structural Overview
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Removing one hydrogen from the intervening CH2 group with both...
Mass Spectrometry: Cycloalkane Fragmentation
In mass spectrometry, cycloalkanes exhibit distinct fragmentation patterns due to the inherent stability of their molecular ions compared to linear or branched alkanes. The ring structure of cycloalkanes provides additional stability to the molecular ions, often resulting in prominent ion peaks in the mass spectrum.
For example, cyclohexane molecular ions have a mass-to-charge ratio (m/z) of 84, which tends to produce a stronger signal than linear alkanes like hexane. This stability comes from...
For example, cyclohexane molecular ions have a mass-to-charge ratio (m/z) of 84, which tends to produce a stronger signal than linear alkanes like hexane. This stability comes from...
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