Photochemical Cycloaddition ([2+2])

2 CH2=CH2 → Cyclobutane

概要

UV light promotes one alkene to its excited state, allowing a symmetry-forbidden [2+2] cycloaddition that cannot occur thermally according to the Woodward–Hoffmann rules. The product is a cyclobutane ring. This is a textbook example of how photochemistry enables reactions impossible by thermal pathways.

参加者

役割 物質 係数 状態
反応物 Ethylene C₂H₄ 2 (g)

日常の例

UV-induced [2+2] cycloaddition between adjacent thymine bases in DNA creates cyclobutane pyrimidine dimers, the main cause of sunburn.

産業上の重要性

[2+2]光環化付加は有機合成における歪み環系の構築や天然物・医薬品の合成に使用される。

特性

タイプ
Photochemical
可逆的
いいえ
エネルギー
発熱性
ΔH
-109.0 kJ/mol

関連する反応

Photochemical Smog Formation (NO₂ Photolysis) Photochromism of Spiropyran Chlorophyll Fluorescence Photodegradation of Methylene Blue by TiO₂ Photodissociation of Chlorine Gas Silver Bromide Photodecomposition Cis-Trans Isomerization of Retinal Photosynthesis Ozone Formation by UV Light Dye-Sensitized Solar Cell (Grätzel Cell)

Frequently Asked Questions

What is the equation for Photochemical Cycloaddition ([2+2])?
The balanced equation is: 2 CH₂=CH₂ → Cyclobutane.
What type of reaction is Photochemical Cycloaddition ([2+2])?
Photochemical Cycloaddition ([2+2]) is a photochemical reaction.
Is Photochemical Cycloaddition ([2+2]) exothermic or endothermic?
Photochemical Cycloaddition ([2+2]) is exothermic (releases energy). The enthalpy change (ΔH) is -109.0 kJ/mol.