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関連する概念動画

Radical Reactivity: Intramolecular vs Intermolecular01:33

Radical Reactivity: Intramolecular vs Intermolecular

Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak carbon–halogen...
Thermal Electrocyclic Reactions: Stereochemistry01:17

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.
Photochemical Electrocyclic Reactions: Stereochemistry01:26

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: Overview01:26

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.
Woodward–Hoffmann Selection Rules and Microscopic Reversibility01:34

Woodward–Hoffmann Selection Rules and Microscopic Reversibility

Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH301:11

ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3

All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...

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関連する実験動画

Updated: Jun 20, 2026

Direct Imaging of Laser-driven Ultrafast Molecular Rotation
10:52

Direct Imaging of Laser-driven Ultrafast Molecular Rotation

Published on: February 4, 2017

回転するトリガーを備えた分子内電子配列.

Shoko Kume1, Kuniharu Nomoto, Tetsuro Kusamoto

  • 1Department of Chemistry, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. kume@chem.s.u-tokyo.ac.jp

Journal of the American Chemical Society
|September 25, 2009
PubMed
まとめ

単一分子のシステムにおける電子の移転は,分子回転によって制御されます. この研究は,フェロセーヌ結合銅複合体が,温度によって酸化還元活性が切り替わり,同期運動と電子移動をどのように示すかを明らかにしています.

科学分野:

  • 超分子化学 超分子化学
  • 分子電子 (モレキュラー・エレクトロニクス)
  • 協調化化学について

背景:

  • 単一分子システムでは,化学的,物理的プロセスを正確に制御できます.
  • 電子の移転は,多くの生物学的および化学的なシステムにとって根本的なものです.
  • 分子運動は電子の性質に影響を与える.

研究 の 目的:

  • 電子の移転が分子運動によって誘発される単一分子システムを構築し,特徴づけること.
  • 分子構成,酸化還元活性,および温度との相互作用を調査する.
  • 同期運動と電子の移動のメカニズムを解明する.

主な方法:

  • アイソメアの構造的特徴化のためのX線結晶学.
  • プロトン核磁気共鳴 ((1) H NMR) спектроскопияで,同位体相互変換を研究する.
  • レドックスポテンシャルを決定するための電気化学測定.
  • 電子パラマグネティック共振 (EPR) とUV-Vis吸収スペクトロスコーピーは,酸化とスペクトルの変化を監視します.

主要な成果:

  • 2つの異なる協調構造を持つフェロセーヌ結合銅複合体を合成した.

さらに関連する動画

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers
08:51

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers

Published on: August 18, 2017

Fluorescence Lifetime Imaging of Molecular Rotors in Living Cells
09:45

Fluorescence Lifetime Imaging of Molecular Rotors in Living Cells

Published on: February 9, 2012

関連する実験動画

Last Updated: Jun 20, 2026

Direct Imaging of Laser-driven Ultrafast Molecular Rotation
10:52

Direct Imaging of Laser-driven Ultrafast Molecular Rotation

Published on: February 4, 2017

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers
08:51

Coulomb Explosion Imaging as a Tool to Distinguish Between Stereoisomers

Published on: August 18, 2017

Fluorescence Lifetime Imaging of Molecular Rotors in Living Cells
09:45

Fluorescence Lifetime Imaging of Molecular Rotors in Living Cells

Published on: February 9, 2012

  • 同位体同士は,室温でピリミジン回転によって相互変換し,233K以下で凍結する.
  • 酸化状態は同位体安定性に影響を及ぼし,自発的な同位体化を引き起こします.
  • 電子移転同一性 (銅対フェロセーン) は,温度と分子運動に基づいて交互に変化します.
  • 一段階のスペクトル変換として観測された同期運動と電子の移動.

    • 結論:

    • 分子回転運動は,単一分子システムで電子の移転を効果的に誘発し,制御することができます.
    • このシステムは,酸化還元センターの温度依存のスイッチングを実証しています.
    • この研究は,構造変化に基づく調節可能な電子特性を持つ分子デバイスの設計に関する洞察を提供します.