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Even‐electron ions: a systematic study of the neutral species lost in the dissociation of quasi‐molecular ions
Author(s) -
Levsen Karsten,
Schiebel HansMartin,
Terlouw Johan K.,
Jobst Karl J.,
Elend Manfred,
Preiß Alfred,
Thiele Herbert,
Ingendoh Arnd
Publication year - 2007
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.1234
Subject(s) - chemistry , ion , dissociation (chemistry) , ionization , electron ionization , molecule , chemical ionization , moiety , density functional theory , mass spectrometry , electrospray ionization , polyatomic ion , ion trap , atmospheric pressure chemical ionization , computational chemistry , stereochemistry , organic chemistry , chromatography
The collision‐induced dissociations of the even‐electron [M + H] + and/or [M − H] − ions of 121 model compounds (mainly small aromatic compounds with one to three functional groups) ionized by electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) have been studied using an ion trap instrument, and the results are compared with the literature data. While some functional groups (such as COOH, COOCH 3 , SO 3 H in the negative ion mode, or NO 2 in both the positive and negative ion modes) generally promote the loss of neutrals that are characteristic as well as specific, other functional groups (such as COOH in the positive ion mode) give rise to the loss of neutrals that are characteristic, but not specific. Finally, functional groups such as OH and NH 2 in aromatic compounds do not lead to the loss of a neutral that reflects the presence of these substituents. In general, the dissociation of [M + H] + and [M − H] − ions generated from aliphatic compounds or compounds containing an aliphatic moiety obeys the even‐electron rule (loss of a molecule), but deviations from this rule (loss of a radical) are sometimes observed for aromatic compounds, in particular for nitroaromatic compounds. Thermochemical data and ab initio calculations at the CBS‐QB3 level of theory provide an explanation for these exceptions. When comparing the dissociation behaviour of the even‐electron [M + H] + and/or [M − H] − ions (generated by ESI or APCI) with that of the corresponding odd‐electron [M] + ions (generated by electron ionization, EI), three cases may be distinguished: (1) the dissociation of the two ionic species differs completely; (2) the dissociation involves the loss of a common neutral, yielding product ions differing in mass by one Da, or (3) the dissociations lead to a common product ion. Copyright © 2007 John Wiley & Sons, Ltd.