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Norrish Reaction

The Norrish reaction is a photochemical reaction involving ketones and aldehydes, named after the chemist Ronald George Wreyford Norrish. It is subdivided into two types: Norrish Type I and Norrish Type II reactions[1][4].

Norrish Type I Reaction

The Norrish Type I reaction involves the photochemical cleavage or homolysis of the α-carbon bond in aldehydes and ketones, resulting in the formation of two radical fragments. This process occurs when the carbonyl group absorbs a photon and is excited to a singlet state, which can then undergo intersystem crossing to a triplet state. The cleavage can happen from either state, leading to radical fragments that can undergo various secondary reactions depending on their molecular structure. These secondary reactions include recombination, loss of carbon monoxide to form a new carbon radical, abstraction of an α-proton to form a ketene and an alkane, or abstraction of a β-proton to form an aldehyde and an alkene[1][4].

Norrish Type II Reaction

The Norrish Type II reaction is characterized by the photochemical intramolecular abstraction of a γ-hydrogen atom by the excited carbonyl compound, leading to the formation of a 1,4-biradical. This biradical can then either recombine to form a cyclobutane compound or undergo fragmentation to yield an enol and an alkene. The reaction was first reported by Norrish in 1937 and has been studied in various contexts, including environmental chemistry and the synthesis of natural products[1][4].

Applications and Scope

The Norrish reactions have been studied for their relevance in environmental chemistry, particularly in the photolysis of aldehydes like heptanal in Earth's atmosphere. They also have applications in the total synthesis of natural products, where they can be used as key steps due to their ability to generate complex structures from simpler carbonyl compounds. Despite their limited synthetic utility, Norrish reactions are important in the photo-oxidation of polymers and in the generation of complex molecular structures in organic synthesis[1][3][4].

Examples in Synthesis

The Norrish reaction has been utilized in several notable syntheses, such as Leo Paquette's 1982 synthesis of dodecahedrane, which involved three separate Norrish-type reactions. Additionally, the reaction has been applied in the total synthesis of biologically active compounds, where optimized conditions can minimize side reactions and provide good yields of desired intermediates[1].

References

The Norrish reaction is significant in the study of photochemistry and has been instrumental in advancing our understanding of the behavior of carbonyl compounds under light irradiation.

Citations:

[1] https://en.wikipedia.org/wiki/Norrish_reaction

[2] https://www.youtube.com/watch?v=-JphUtBXSLI

[3] https://link.springer.com/article/10.1007/s43630-021-00100-3

[4] https://www.chemeurope.com/en/encyclopedia/Norrish_reaction.html

[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9945184/

[6] https://www.semanticscholar.org/paper/Applications-of-Norrish-type-I-and-II-reactions-in-Majhi/5397309bc99b6723bbc14833512828af36298686

[7] https://en.chem-station.com/reactions-2/2017/06/norrish-reaction.html

[8] https://www.chemistryworld.com/opinion/norrish-photolytic-cleavage/3010125.article

[9] https://www.academia.edu/68194831/Applications_of_Norrish_type_I_and_II_reactions_in_the_total_synthesis_of_natural_products_a_review

[10] https://www.youtube.com/watch?v=KxaWdXUd5ek

[11] https://www.slideshare.net/NileshMore44/photochemistry-of-carbonyl-compound-norrish-type-i-and-type-ii-reaction

[12] https://www.sciencedirect.com/topics/chemistry/norrish-reaction

[13] https://en.chem-station.com/reactions-2/2016/02/norrish-yang-reaction.html

[14] https://en.wiktionary.org/wiki/Norrish_reaction

[15] https://www.youtube.com/watch?v=GWbPA9mbKSY

[16] https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Radical_Reactions_of_Carbohydrates_%28Binkley%29/Radical_Reactions_of_Carbohydrates_II:_Radical_Reactions_of_Carbohydrates/10:_Aldehydes_and_Ketones/06._Ketone_Photolysis

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