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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:
    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.
    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.
    This reaction should be distinguished from an alpha-(α-)elimination.
    PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 302
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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: (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
Last update: 2014-02-24; version: 2.3.3.
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