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|Type:||Artigo de periódico|
|Title:||Structurally Diagnostic Ion-molecule Reactions: Acylium Ions With α-, β- And γ-hydroxy Ketones|
|Abstract:||Gas-phase reactions of four acylium ions and a thioacylium ion with three isomeric α-, β- and γ-hydroxy ketones are performed by pentaquadrupole mass spectrometric experiments. Novel structurally diagnostic reactions are observed, and found to correlate directly with interfunctional group separation. All five ions tested (CH3CO+, CH2=CHCO+, PhCO+, (CH3)2NCO+ and (CH3)2NCS+) react with the γ-hydroxy ketone (5-hydroxy-2-pentanone) to form nearly exclusively a cyclic oxonium ion of m/z 85 that formally arises from hydroxy anion abstraction. With the β-hydroxy ketone (4-hydroxy-2-pentanone), CH2=CHCO+, PhCO+ and (CH3)2NCO+ form adducts that undergo fast cyclization via intramolecular water displacement, yielding resonance-stabilized cyclic dioxinylium ions. With the α-hydroxy ketone (3-hydroxy-3-methyl-2-butanone), PhCO+, (CH3)2NCO+ and (CH3)2NCS+ form stable adducts. Evidence that these adducts display cyclic structures is provided by the triple-stage mass spectra of the (CH3)2NCS+ adduct; it dissociates to (CH3)2NCO+ via a characteristic reaction-dissociation pathway that promotes sulfur-by-oxygen replacement. If cyclizations are assumed to occur with intramolecular anchimeric assistance, relationships between structure and reactivity are easily recognized. Copyright © 2001 John Wiley & Sons, Ltd.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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