定义Definition
诺里什反应是酮和醛受光激发后发生的两类光化学裂解：I 型为羰基与 α-碳之间的键均裂生成两个自由基；II 型为激发态羰基夺取 γ-氢，生成 1,4-双自由基，随后断裂成烯醇（酮）和烯烃，或闭环成环丁醇。
The Norrish reactions are two photochemical processes of excited ketones and aldehydes: type I is homolysis of the bond between the carbonyl carbon and the α-carbon, giving two radicals; type II is abstraction of a γ-hydrogen by the excited carbonyl, giving a 1,4-biradical that cleaves to an enol (then ketone) and an alkene, or closes to a cyclobutanol.
I 型Type I
n→π* 激发后 α-键断裂得到酰基自由基和烷基自由基；酰基自由基可脱去 CO，再与烷基自由基重新结合或夺氢。
After n→π* excitation the α bond breaks to give an acyl radical and an alkyl radical; the acyl radical may lose CO before recombining or abstracting hydrogen.
II 型Type II
激发态羰基氧经六元环过渡态夺取 γ-H，生成 1,4-双自由基；β-键断裂得到烯醇和烯烃（裂解），或两自由基结合得到环丁醇（杨氏环化 Yang cyclisation）。
The excited oxygen abstracts a γ-H through a six-membered transition state, giving a 1,4-biradical; β-cleavage gives an enol and an alkene, or radical coupling gives a cyclobutanol (Yang cyclisation).
由来与应用Origin and uses
英国化学家罗纳德·诺里什在 1930 年代系统研究了羰基化合物的光解，他因快速反应（闪光光解）研究与波特、艾根共获 1967 年诺贝尔化学奖。诺里什反应与聚合物光降解、大气中醛酮的光化学密切相关。
The British chemist Ronald Norrish studied carbonyl photolysis systematically in the 1930s; he shared the 1967 Nobel Prize in Chemistry with Porter and Eigen for work on fast reactions (flash photolysis). Norrish reactions underlie polymer photodegradation and atmospheric carbonyl photochemistry.
反应Reactions
紫外光照射，气相或溶液
UV irradiation, gas phase or solution
羰基 n→π* 激发（单线态或三线态）。
n→π* excitation of the carbonyl (singlet or triplet).
I 型：α-C–C 均裂；II 型：1,5-氢转移生成 1,4-双自由基。
Type I: α C–C homolysis; type II: 1,5-hydrogen shift giving a 1,4-biradical.
自由基脱羰、重组、断裂或环化得到产物。
Radicals decarbonylate, recombine, fragment or cyclise to products.
典型的 II 型裂解。
A typical type II cleavage.
年表Timeline
- 1930s
诺里什研究醛酮光解
Norrish studies the photolysis of aldehydes and ketones
- 1958
杨念祖报道 II 型双自由基环化成环丁醇
N. C. Yang reports cyclobutanol formation from type II biradicals
- 1967
诺里什获诺贝尔化学奖
Norrish shares the Nobel Prize in Chemistry