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

Alpha cleavage, (α-cleavage) in organic chemistry, refers to the act of breaking the carbon-carbon bond,Hathaway, Bruce A. Organic chemistry the easy way Barron's Educational Series Woodbury, N.Y 2005 0-7641-2794-2 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 315 adjacent to the carbon bearing a specified functional group. http://goldbook.iupac.org/A00004.html α-cleavage (alpha-cleavage) 2008-07-08 IUPAC Compendium of Chemical Terminology (Gold Book) IUPAC Mass spectrometry Generally this topic is discussed when covering mass spectrometry and occurs generally by the same mechanisms. 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 10.1351/pac199163101541 α-cleavage (alpha-cleavage) A00004 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 In photochemistry, it is the homolytic cleavage of a bond adjacent to a specified group. Verhoeven, J. W. 1996 Glossary of terms used in photochemistry (IUPAC Recommendations 1996) Pure and Applied Chemistry 68 2223 10.1351/pac199668122223 References