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Examination of Ortho effects in the collisionally activated dissociation of closed‐shell aromatic ions
Author(s) -
Donovan Tracy,
Brodbelt Jennifer
Publication year - 1992
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210270104
Subject(s) - chemistry , dissociation (chemistry) , ion , mass spectrometry , electron ionization , quadrupole ion trap , photochemistry , mass spectrum , proton affinity , ether , ion trap , ionization , protonation , organic chemistry , chromatography
The collisionally activated dissociation of a variety of isomeric disubstituted aromatic ions formed by ion–molecule reactions were examined in order to characterize ortho effects in closed‐shell systems. Closed‐shell ions of methoxyacetophenone, hydroxyacetophenone, methoxyphenol, anisaldehyde and hydroxybenzaldehyde were formed by proton transfer, methyl addition or methyne addition by using dimethyl ether or ethylene oxide as chemical ionization reagents, and then the structures of these adducts were studied by deuterium‐labelling methods and by collisionally activated dissociation techniques in a triple quadrupole mass spectrometer or a quadrupole ion trap. Typically, the meta and para isomers have qualitatively similar dissociation spectra which reflect the types of dissociation reactions observed for the corresponding monosubstituted aromatic ions. The predominant dissociation pathways of the [M + H] + and [M + 15] + ions are directed by the electron‐withdrawing substituents, whereas the major dissociation pathways of the [M + 13] + ions are related to the electron‐releasing substituent. In contrast, the dissociation routes of the corresponding ortho isomers are dramatically different. This is attributed to the opportunity for functional group interactions of the ortho isomers which facilitate alternative pathways.