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|Type:||Artigo de periódico|
|Title:||Double transacetalization of diacylium ions|
|Abstract:||A novel gas-phase reaction of diacylium ions of the O=C=X+=C=O type (X = N, CH) is reported: double transacetalization with cyclic acetals or ketals, The reaction is exothermic and highly efficient, and forms members of a new class of highly charged-delocalized ions: cyclic ionic diketals, Pentaquadrupole double-and triple-stage mass spectrometric (MS2 and MS3) experiments reveal the high double transacetalization reactivity of O=C=N+=C=O and O=C=CH+=C=O, whereas the synthesis of differently substituted cyclic ionic diketals is performed in MS3 experiments via sequential mono- and double transacetalization of O=C=N+=C=O and O=C=CH+=C=O with different acetals, With cyclic acetals, the acylium-thioacylium ion O=C=N+=C=S reacts promptly and selectively by mono-transacetalization at its acylium site, but the free thiacylium site of its cyclic ionic ketal is nearly unreactive by double transacetalization. Therefore, only the acylium site of O=C=N+=C=S can be efficiently protected by transacetalization, Low-energy MS3 collision-induced dissociation of the cyclic ionic diketals of O=C=N+=C=O and O=C=CH+=C=O sequentially frees each of the protected acylium site to form the mono-derivatized ion, and then the fully deprotected diacylium ion. Copyright (C) 2000 John Wiley & Sons, Ltd.|
|Editor:||John Wiley & Sons Ltd|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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