电子转移在2,7-丁尼特罗纳甲烯基基离子中发生
Stephen F Nelsen1, Michael N Weaver, Asgeir E Konradsson
1Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, WI 53706-1396, USA. nelsen@chem.wisc.edu
Journal of the American Chemical Society
|November 26, 2004
概括
在2,7-丁纳基离子中,分子内电子转移发生得很快,速度常数高达10^9 s^-1. 马库斯-赫什理论成功地描述了这一过程,排除了电子跳跃机制.
科学领域:
- 物理化学 物理化学
- 频谱学是一种光谱学.
- 量子化学 是一个量子化学.
背景情况:
- 研究分子内电子转移 (IET) 对于理解分子系统中的电荷传输至关重要.
- 2,7-丁纳烯基离子作为研究IET动态的模型系统.
研究的目的:
- 为了确定 2,7-dinitronaphthalene 基离子中分子内电子转移的速率常数.
- 评估马库斯-赫什理论在描述观察到的电子转移动态方面的适用性.
- 将实验结果与结构性和能量性质的理论计算进行比较.
主要方法:
- 通过各种烯溶剂中的合金还原生成2,7-丁纳烯基离子.
- 光学光谱学观察间隔电荷转移 (IVCT) 频段.
- 电子自旋共振 (ESR) 光谱法用于测量电子转移速率常数.
- 紫外可见 (UHF) 和半实证AM1计算与配置相互作用和溶剂模型.
主要成果:
- 在1070nm观察到一个IVCT带,表明有效的分子内电子转移.
- 电子自旋共振 (ESR) 测量结果显示,在293 K时的互波速率常数为3.1 x 10^9 s^-1.
- 马库斯-赫什理论准确地预测了速率常数,支持一种非跳跃电子转移机制.
- 理论计算预测了一个平面的,不对称的结构,并强调了溶剂重组能量的主导地位.
结论:
- 这项研究证实了 2,7-dinitronaphthalene 基离子中的快速内分子电子转移,与经典的马库斯-赫什理论相一致.
- 这些发现排除了电子跳跃机制,强调了分子内动力学的重要性.
- 计算结果提供了对控制电子转移的分子结构和能量格局的洞察.
相关概念视频
SN2 Reaction: Transition State
An SN2 reaction of an alkyl halide is a single-step process in which bond formation between the nucleophile and the substrate and bond breaking between the substrate and the halide occurs simultaneously through a transition state without forming an intermediate.
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
E2 Reaction: Kinetics and Mechanism
SN2 substitutions and E2 eliminations of alkyl halides proceed via a concerted pathway. While the nucleophile attacks the alpha carbon in SN2 reactions, it functions as a strong base and abstracts a beta hydrogen in the E2 mechanism. The rate-limiting transition state in E2 elimination reactions is characterized by partially broken carbon–hydrogen and carbon–halogen bonds and a partially formed pi bond between the alpha and beta carbons. The beta hydrogen and halide are eliminated...
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.
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
UV–Vis Spectroscopy: Molecular Electronic Transitions
In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this process,...
Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene
Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.


