Alpha cleavage

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=|accessdate=] adjacent to the carbon bearing a specified functional group. [ cite web|url= |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 spectrometry and 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 McLafferty rearrangement.

In 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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