词条 | Norrish reaction |
释义 |
The Norrish reaction in organic chemistry describes the photochemical reactions taking place with ketones and aldehydes. This type of reaction is subdivided in Norrish type I reactions and Norrish type II reactions.[1] The reaction is named after Ronald George Wreyford Norrish. Type IThe Norrish type I reaction is the photochemical cleavage or homolysis of aldehydes and ketones into two free radical intermediates. The carbonyl group accepts a photon and is excited to a photochemical singlet state. Through intersystem crossing the triplet state can be obtained. On cleavage of the α-carbon bond from either state, two radical fragments are obtained.[2] The size and nature of these fragments depends upon the stability of the generated radicals; for instance, the cleavage of 2-butanone largely yields ethyl radicals in favor of less stable methyl radicals.[3] Several secondary reaction modes are open to these fragments depending on the exact molecular structure.
The synthetic utility of this reaction type is limited, for instance it often is a side reaction in the Paternò–Büchi reaction. One organic synthesis based on this reaction is that of bicyclohexylidene.[6] Type IIA Norrish type II reaction is the photochemical intramolecular abstraction of a γ-hydrogen (a hydrogen atom three carbon positions removed from the carbonyl group) by the excited carbonyl compound to produce a 1,4-biradical as a primary photoproduct.[7] Norrish first reported the reaction in 1937.[8] Secondary reactions that occur are fragmentation to form an enol and an alkene, or intramolecular recombination of the two radicals to a substituted cyclobutane (the Norrish–Yang reaction).[9] ScopeThe Norrish reaction has been studied in relation to environmental chemistry with respect to the photolysis of the aldehyde heptanal, a prominent compound in Earth's atmosphere.[10] Photolysis of heptanal in conditions resembling atmospheric conditions results in the formation of 1-pentene and acetaldehyde in 62% chemical yield together with cyclic alcohols (cyclobutanols and cyclopentanols) both from a Norrish type II channel and around 10% yield of hexanal from a Norrish type I channel (the initially formed n-hexyl radical attacked by oxygen). In one study [11] the photolysis of an Acyloin derivative in water in presence of hydrogen tetrachloroaurate (HAuCl4) generated nanogold particles with 10 nanometer diameter. The species believed to responsible for reducing Au3+ to Au0 [12] is the Norrish generated ketyl radical. Paquette's 1982 synthesis of dodecahedrane involves three separate Norrish-type reactions in its approximately 29-step sequence. An example of a synthetically useful Norrish type II reaction can be found early in the total synthesis of the biologically active cardenolide ouabagenin by Baran and coworkers.[13] The optimized conditions minimize side reactions, such as the competing Norrish type I pathway, and furnish the desired intermediate in good yield on a multi-gram scale. See also
References1. ^Named Organic Reactions, 2nd Edition, Thomas Laue and Andreas Plagens, John Wiley & Sons: Chichester, England, New York, 2005. 320 pp. {{ISBN|0-470-01041-X}} {{DEFAULTSORT:Norrish Reaction}}2. ^1 {{Cite web|url = http://goldbook.iupac.org/N04219.html|title = IUPAC Gold Book - Norrish Type I photoreaction|date = 24 February 2014|doi = 10.1351/goldbook.N04219|accessdate = 31 March 2014|publisher = IUPAC}} 3. ^{{cite journal|last1=Blacet|first1=F. E.|last2=N. Pitts Jr.|first2=James|title=Methyl Ethyl Ketone Photochemical Processes|journal=Journal of the American Chemical Society|date=1950|volume=72|issue=6|pages=2810–2811|doi=10.1021/ja01162a544}} 4. ^{{cite journal|last1=Yang|first1=Nien-Chu|last2=D. Feit|first2=Eugene|last3=Hui|first3=Man Him|last4=Turro|first4=Nicholas J.|last5=Dalton|first5=Christopher|title=Photochemistry of di-tert-butyl ketone and structural effects on the rate and efficiency of intersystem crossing of aliphatic ketones|journal=Journal of the American Chemical Society|date=1970|volume=92|issue=23|pages=6974–6976|doi=10.1021/ja00726a046}} 5. ^{{cite journal|last1=Abuin|first1=E.B.|last2=Encina|first2=M.V.|last3=Lissi|first3=E.A.|title=The photolysis of 3-pentanone|journal=Journal of Photochemistry|date=1972|volume=1|issue=5|pages=387–396|doi=10.1016/0047-2670(72)80036-4}} 6. ^Bicyclohexylidene Nicholas J. Turro, Peter A. Leermakers, and George F. Vesley Organic Syntheses, Coll. Vol. 5, p.297 (1973); Vol. 47, p.34 (1967) Online article. 7. ^{{Cite web|url = http://goldbook.iupac.org/N04218.html|title = IUPAC Gold Book - Norrish Type II photoreaction|date = 24 February 2014|doi = 10.1351/goldbook.N04218|accessdate = 31 March 2014|publisher = IUPAC}} 8. ^{{Cite journal|title = Photo-decomposition of Aldehydes and Ketones|date = 31 July 1937|doi = 10.1038/140195b0|last = Norrish|first = R. G. W.|last2 = Bamford|first2 = C. H.|journal = Nature|volume = 140|pages = 195–6|bibcode = 1937Natur.140..195N}} 9. ^{{Cite web|url = http://goldbook.iupac.org/NT07427.html|title = IUPAC Gold Book - Norrish–Yang reaction|date = 24 February 2014|doi = 10.1351/goldbook.NT07427|accessdate = 31 March 2014|publisher = IUPAC}} 10. ^Photolysis of Heptanal Suzanne E. Paulson, De-Ling Liu, Grazyna E. Orzechowska, Luis M. Campos, and K. N. Houk J. Org. Chem.; 2006; 71(17) pp 6403 - 6408; (Article) {{DOI|10.1021/jo060596u}} 11. ^Facile Photochemical Synthesis of Unprotected Aqueous Gold Nanoparticles Katherine L. McGilvray, Matthew R. Decan, Dashan Wang, and Juan C. Scaiano J. Am. Chem. Soc.; 2006; 128(50) pp 15980 - 15981; (Communication) {{DOI|10.1021/ja066522h}} 12. ^Technically Au3+ is reduced to Au2+ which then forms Au+ and Au3+ by disproportionation followed by final reduction of Au1+ to Auo 13. ^{{cite journal|last=Renata|first=H.|author2=Zhou, Q. |author3=Baran, P. S. |title=Strategic Redox Relay Enables A Scalable Synthesis of Ouabagenin, A Bioactive Cardenolide|journal=Science|date=3 January 2013|volume=339|issue=6115|pages=59–63|doi=10.1126/science.1230631|pmid=23288535|pmc=4365795|bibcode=2013Sci...339...59R}} 3 : Free radical reactions|Photochemistry|Name reactions |
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