Photochemical Cycloaddition ([2+2])

2 CH2=CH2 → Cyclobutane

개요

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.

참여 물질

역할 물질 계수 상태
반응물 Ethylene C₂H₄ 2 (g)

일상 속 예시

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

산업적 중요성

[2+2] 광환화 첨가는 유기 합성에서 비틀림 고리계 구축과 천연물 및 의약품 합성에 사용됩니다.

성질

유형
Photochemical
가역 반응
아니오
에너지
발열
ΔH
-109.0 kJ/mol

관련 반응

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.