Fragmentation reactions of the enolate ions of 2-pentanone

✍ Scribed by Allen Donnelly; Swapan Chowdhury; Alex. G. Harrison

• Publisher: John Wiley and Sons
• Year: 1989
• Tongue: English
• Weight: 497 KB
• Volume: 24
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/oms.1210240206

✦ Synopsis

The reaction of [OH]-with Zpentanone produces two enolate ions, (CH,CH,CH,COCH,]-and [CH,COCHCH,CHJ -, by proton abstraction from C(l) and C(3), respectively. Using deuterium isotopic labelling the fragmentation reactions of each enolate have been delineated for collisional activation at both high (8 keV) and low (5-100 eV) collisional energies. The primary enolate ion fragments mainly by elimination of ethene. Two mechanisms operate: elimination of C(4) and C(5) with hydrogen migration from C(5), and elimination of C(3) and C(4) with migration of the C(5) methyl group. Minor fragmentation of the primary enolate also occurs by elimination of propane and elimination of C,H,; the latter reaction involves specifically the terminal ethyl group. The secondary enolate ion fragments mainly by loss of H, and by elimination of CH,; for the latter reaction four different pathways are operative. Minor elimination of ethene also is observed involving migration of a C(5) hydrogen to C(3) and elimination of C(4) and C(5) as ethene.