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α-cleavage (alpha-cleavage)

  1. (in mass spectrometry) The fission of a bond originating at an atom which is adjacent to one assumed to bear the charge; the definition of β-, γ-, cleavage then follows automatically. The process:
    A00004
    would thus be described as α-fission of a ketone with expulsion of a radical R1. . The carbon atoms of the radical R1. are called the α-, β-, γ-carbons, starting with the atom nearest the functional group.
    Source:
    PAC, 1991, 63, 1541 (Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)) on page 1558
  2. (in photochemistry) Homolytic cleavage of a bond connecting an atom or group to an excited chromophore. Often applied to a bond connected to a carbonyl group, in which case it is called a Norrish type I photoreaction.
    Note:
    This reaction should be distinguished from an alpha-(α-)elimination.
    Source:
    PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 302
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Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook.
Last update: 2014-02-24; version: 2.3.3.
DOI of this term: doi:10.1351/goldbook.A00004.
Original PDF version: http://www.iupac.org/goldbook/A00004.pdf. The PDF version is out of date and is provided for reference purposes only. For some entries, the PDF version may be unavailable.
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