1,3-二極体による二極性特性と,エチレンまたはアセチレンに対するその反応性との間には明確な相関がある

Benoit Braida¹, Christof Walter, Bernd Engels

¹CNRS UMR 7616, Laboratoire de Chimie Théorique, UPMC Université Paris 06, Case Courrier 137, 4 Place Jussieu, 75252 Paris, France. braida@lct.jussieu.fr

Journal of the American Chemical Society

|May 21, 2010

まとめ

1,3-二極のジラジカルな性質は,1,3-二極のサイクル添加反応において極めて重要です. 提案されたメカニズムは,二極歪曲を反応性二基状態に含み,障壁のないサイクル添加を可能にします.

科学分野:

コンピューティング・ケミストリー
有機化学オーガニック・ケミストリー
量子化学とは,量子化学である.

背景:

1,3-二極サイクロアディションは,有機合成における基本的な反応である.
1,3-二極体の電子構造を理解することは,反応性を制御する鍵です.
以前の研究で,これらの反応におけるダイラジカル性の重要性について示唆されていた.

研究の目的:

様々な1,3-ディポールのダイラジカル性質を定量的に評価する.
ダイラジカルな性質とサイクロアディションの障壁との関係を調査する.
1,3-二極循環加減のメカニズムモデルを提案する.

主な方法:

呼吸-軌道バレンスの結合 (BOVB) メソッドを用いた Ab initio 計算.
1,3-二極電子構造を,バレンスの結合構造の線形組み合わせとして分析する.
電子特性と反応障壁の相関分析.

主要な成果:

9つの1,3-二極体 (ディアゾニウムベタイン,ニトリリウムベタイン,アゾメチンベタイン) の二極性特性は定量的に推定された.
エチレンとアセチレンに対するダイラジカル性質とサイクル添加障壁の間の強い線形相関が発見されました.
ダイラジカルな性質は,1,3-ディポールの歪曲により,移行状態に大きく増加します.

結論:

1,3-二極のダイラジカルな性質は,1,3-二極のサイクロアディションを好む重要な要因である.
提案されたメカニズムは,最初の二極歪曲を反応性二基状態に含み,その後,障壁のないサイクル添加を行います.
このモデルは,歪み/相互作用エネルギーモデルと整合し,異なる二極性動物のための同様の障壁を説明します.

さらに関連する動画

06:46

Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

Published on: June 21, 2017

10:12

Retropinacol/Cross-pinacol Coupling Reactions - A Catalytic Access to 1,2-Unsymmetrical Diols

Published on: April 4, 2014

関連する概念動画

01:11

Radical Reactivity: Overview

Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired molecule. These three...

01:29

Diels–Alder Reaction: Characteristics of Dienes

The Diels–Alder reaction brings together a diene and a dienophile to form a six-membered ring. Both components have unique characteristics that influence the rate of the reaction.
Characteristics of the diene
Conformation
The simplest example of a diene is 1,3-butadiene, an acyclic conjugated π system. At room temperature, the molecule exists as a mixture of s-cis and s-trans conformers by virtue of rotation around the carbon–carbon single bond. Although the s-trans isomer is more stable, the...

01:10

Radical Reactivity: Steric Effects

The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic factors, steric factors also account...

01:16

Radical Reactivity: Nucleophilic Radicals

Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For instance, consider...

01:02

Radical Reactivity: Electrophilic Radicals

Radicals adjacent to electron‐withdrawing groups are called electrophilic radicals. These radicals readily react with nucleophilic alkenes. For example, the malonate radical, in which the radical center is flanked by two electron‐withdrawing groups, reacts readily with butyl vinyl ether, which consists of an electron‐donating oxygen substituent. The reaction between electrophilic malonate radical and nucleophilic vinyl ether is favored because the radical has a low‐energy SOMO, which interacts...

01:20

Radical Reactivity: Concentration Effects

In a radical reaction, the concentration of starting materials governs the selectivity of a radical. For example, the reaction between an alkyl halide and an alkene, in the presence of tin hydride and AIBN, begins with the generation of a tin radical. The generated radical then abstracts halogen from the alkyl halide, producing an alkyl radical. This alkyl radical can either react with tin hydride, yielding an alkane, or add to an alkene, generating a nitrile-stabilized radical, eventually...

関連する実験動画