- Alpha cleavage
Alpha cleavage, (α-cleavage) in
organic chemistry, refers to the act of breaking the carbon-carbon bond,cite book |author=Hathaway, Bruce A. |authorlink= |editor= |others= |title=Organic chemistry the easy way |edition= |language= |publisher=Barron's Educational Series |location=Woodbury, N.Y |year=2005 |origyear= |pages= p315|quote= |isbn=0-7641-2794-2 |oclc= |doi= |url= http://books.google.com/books?id=fjy2oJuJ_0kC&pg=PA315&dq=%22Alpha+cleavage%22+%22carbon-carbon+bond%22&lr=lang_en&num=20&as_brr=3&ei=LsVySOaJNZOkiwGD_LgO&sig=ACfU3U3IlpMzSiZN4SPDARQjeuWcUVZLyA|accessdate=] adjacent to the carbon bearing a specified functional group. [ cite web|url=http://goldbook.iupac.org/A00004.html |title=α-cleavage (alpha-cleavage) |accessdate=2008-07-08 |work=IUPAC Compendium of Chemical Terminology (Gold Book) |publisher=IUPAC ]
Generally this topic is discussed when covering
mass spectrometryand occurs generally by the same mechanisms.cite journal | author = Todd, J. F. J. | year = 1991 | title = Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991) | journal = Pure and Applied Chemistry | volume = 63 | pages = 1541 | doi = 10.1351/pac199163101541 ]
For example of a mechanism of alpha cleavage, an electron is knocked off an atom (usually by electron collision) to form a radical cation. Electron removal generally happens in the following order.
#Lone pair electrons
# Pi Bond Electrons
#Lastly - Sigma Bond Electrons
One of the lone pair electrons moves down to form a pi bond with an electron from an adjacent (alpha) bond.The other electron from the bond moves to an adjacent atom (not one adjacent to the lone pair atom) creating a radical. This creates a double bond adjacent to the lone pair atom (oxygen is a good example) and breaks/cleaves the bond from which the two electrons were removed.
Example C-C-(O::)-H > C-C-(O:.+)-H > C' + (C=O:+)-H where : is a lone pair + is a positive charge and ' is a radical/free electron
In molecules containing carbonyl groups, often competes with
photochemistry, it is the homolytic cleavage of a bond adjacent to a specified group.cite journal | author = Verhoeven, J. W. | year = 1996 | title = Glossary of terms used in photochemistry (IUPAC Recommendations 1996) | journal = Pure and Applied Chemistry | volume = 68 | pages = 2223 | doi = 10.1351/pac199668122223 ]
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