Term: Norrish Type I photoreaction
https://doi.org/10.1351/goldbook.N04219

Definition:
α-Cleavage of an excited carbonyl compound leading to an acyl-alkyl radical pair (from an acyclic carbonyl compound) or an acyl-alkyl diradical (from a cyclic carbonyl compound) as a primary photoproduct.

Notes:
0) An example is: N04219.png
1) Decarbonylation of the primary diradical formed from cyclic @C00844@ and subsequent recombination of the @B00671@ afford very interesting cyclic compounds.

Related Terms:
1) carbonyl compounds (http://doi.org/10.1351/goldbook.C00844).
2) biradical (http://doi.org/10.1351/goldbook.B00671).

Image: Norrish Type I photoreaction (https://goldbook.iupac.org/img/inline/N04219.png) 

Source: PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 375 (https://doi.org/10.1351/pac200779030293)

Citation: 'Norrish Type I photoreaction' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.N04219

License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms.

Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.