相关实验视频

Updated: Aug 19, 2025

Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization

Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization

Published on: November 29, 2018

1,3-环二烯的光化学环开反应:确定真实反应状态

Oksana Travnikova¹, Tomislav Piteša², Aurora Ponzi²

¹Sorbonne Université, CNRS, Laboratoire de Chimie Physique-Matière et Rayonnement, LCPMR, ParisF-75005, France.

Journal of the American Chemical Society

|November 29, 2022

概括

1,3-环二烯到1,3,5-二烯的光化学环开放涉及比以前想象的更复杂的电子状态演变. 一个高的电子状态显著影响了环开放反应路径.

科学领域:

摄影化学
化学反应动力学
量子化学

背景情况:

1,3-环二烯到1,3,5-二烯的光化学异构化是一种已被充分研究的环反应.
之前的模型提出了一条涉及激发到明亮状态,形交叉和通过双倍激发状态的途径.

研究的目的:

阐明精确的电子状态动态,控制1,3-环二烯的环开异构.
挑战人们对反应机制的传统理解.

主要方法:

进行联合实验和计算调查.
通过先进的光谱技术.
进行量子化学计算.

主要成果:

反应途径比标准模型更复杂.
一个高度的电子状态,以前没有强调, 起着至关重要的作用.
这种状态沿着反应坐标平稳地减少能量.

结论:

循环二烯异构化的已确定的机制需要修订.
对于理解光化学反应而言,最初高层电子状态的参与至关重要.

更多相关视频

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Published on: March 20, 2017

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

Published on: November 21, 2017

相关概念视频

Photochemical Electrocyclic Reactions: Stereochemistry

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

Thermal and Photochemical Electrocyclic Reactions: Overview

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.

Thermal Electrocyclic Reactions: Stereochemistry

Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.

Cycloaddition Reactions: MO Requirements for Photochemical Activation

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.

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic movement of six π electrons: four π electrons from the diene and two π electrons from the dienophile.

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction

The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.