Generation and Characterization of Distonic Dehydrophenoxide Radical Anions under Electrospray and Atmospheric Pressure Chemical Ionizations

Document Type

Article

Publication Title

International Journal of Mass Spectrometry

Department

Chemistry

ISSN

1387-3806

Volume

299

Issue

2--3

DOI

10.1016/j.ijms.2010.10.025

First Page

169

Last Page

177

Publication Date

1-1-2011

Abstract

We have explored the possibilities of generating radical anions under electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) conditions. By using different sets of ortho-, meta-, and para-isomers of nitrobenzoic acids, methylphenols, and nitrophenols, and m-, and p-isomers of hydroxybenzaldehydes and hydroxyacetophenones as the precursor molecules, we have successfully generated the isomeric distonic dehydrophenoxide radical anions (m/z 92) using the ESI process by applying relatively high capillary voltages, the in-source dissociation (ISD) condition. Under the same conditions, the o-hydroxybenzaldehyde and the o-hydroxyacetophenone yielded the even-electron dehydrophenoxide anion (m/z 93) due to the well-known ortho-effect. The distonic phenoxide radical anions at m/z 92 were also generated under APCI-ISD conditions by using m- and p-isomers of nitrobenzaldehydes and nitroacetophenones. While the o-nitrobenzaldehyde and the o-nitroacetophenone mainly yielded the phenoxide anion at m/z 93, due to the ortho-effect. The collision-induced dissociation (CID) experiments of all the anionic precursor molecules formed from either ESI or APCI produced comparable mass spectra as those observed in the ESI-ISD or the APCI-ISD experiments. The radical anions at m/z 92 reacted with CO2 and O2 to form the CO2 adduct and the oxygen atom abstraction product, respectively, revealing the dual-character of the distonic radical anions, the phenide ion and the phenyl radical. Computational studies support the results of the ion-molecule reactions.

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