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Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Alpha cleavage

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Alpha cleavage, (α-cleavage) in organic chemistry, refers to the act of breaking the carbon-carbon bond,[1] adjacent to the carbon bearing a specified functional group.[2]

Mass spectrometry

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Generally this topic is discussed when covering mass spectrometry and occurs generally by the same mechanisms.[3][4]

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: 1) lone pair electrons, 2) pi bond electrons, 3) 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.

Photochemistry

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In photochemistry, it is the homolytic cleavage of a bond adjacent to a specified group.[4][5]

References

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  1. ↑ Hathaway, Bruce A. (2005). Organic chemistry the easy way. Woodbury, N.Y: Barron's Educational Series. p. 315. ISBN 0-7641-2794-2.
  2. ↑ "α-cleavage (alpha-cleavage)". IUPAC Compendium of Chemical Terminology (Gold Book). IUPAC. Retrieved 2008-07-08.
  3. ↑ Todd, J. F. J. (1991). "Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)". Pure and Applied Chemistry. 63: 1541. doi:10.1351/pac199163101541.
  4. ↑ a b International Union of Pure and Applied Chemistry. "α-cleavage (alpha-cleavage)". Compendium of Chemical Terminology Internet edition.
  5. ↑ Verhoeven, J. W. (1996). "Glossary of terms used in photochemistry (IUPAC Recommendations 1996)". Pure and Applied Chemistry. 68: 2223. doi:10.1351/pac199668122223.
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