Ketalization of gaseous acylium ions

• Published in: Journal of the American Society for Mass Spectrometry 2001-02, Vol.12 (2), p.150-162
• Main Authors: Moraes, Luis Alberto B, Eberlin, Marcos N
• Format: Article
• Language: English
• Subjects: Analogs; Carbonyl compounds; Carbonyls; Chemistry; Deactivation; Diols; Exact sciences and technology; Mass spectrometry; Mathematical analysis; Organic chemistry; Reactivity and mechanisms; Selectivity
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1016/S1044-0305(00)00211-7

A novel reaction of gaseous acylium ions: ketalization with diols and analogs, has been systematically studied via pentaquadrupole MS 2 and MS 3 experiments and ab initio calculations. A variety of α,β-diols and their amino, thiol, ether, and thioether analogs have been tested for reactivity, mechanism evaluation, site selectivity, and for the effects of α- and β-interfunctional separation. As for condensed-phase ketalization of neutral carbonyl compounds followed by hydrolysis, gaseous acylium ions are chemically deactivated in the form of cyclic ionic ketals by ketalization, and are efficiently released via on-line collision-induced dissociation. Ketalization of acylium ions is shown to identify and structurally characterize α,β-diols and their analogs, and to distinguish regioisomers. Diastereomers can also be distinguished, as illustrated for cis and trans 1,2-diaminocyclohexane. The MS 2 and MS 3 data together with 18O-labeling and ab initio calculations establish for acylium ion ketalization a mechanism of anchimeric assistance with participation of the neighboring acyl group.