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Exploring rearrangements along the fragmentation pathways of diuron anion: A combined experimental and computational investigation.
Int. J. Mass Spectrom. 288, 6-15 (2009)
Diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), a common herbicide from phenyl urea class, was investigated by studying the formation of several negative ions [M−H]− in the gas phase and the fragmentation behaviour of the thermodynamically most probably formed isomeric anions upon linear ion acceleration/collision experiments. The collision induced dissociation experiments (CID) were carried out in a hexapole–quadrupole–hexapole hybrid system coupled to 12 T magnet with infinity ICR cell for high resolution measurements. Two distinctive main pathways were observed in the MS/MS spectrum. Sustained off-resonance irradiation (SORI) experiments inside the ICR cell reinforce the fragmentation channels obtained from linear ion acceleration experiments. The fragmentation pathways were also completely investigated by the use of B3LYP/6-311+G(2d,p)//B3LYP/6-31+G(d) level of theory. Elimination of dimethylamine takes place in a two-step process, by which two successive 1,3 proton shifts occur. The second 1,3 proton shift is concerted with the departure of dimethylamine. The driving force for the (CH3)2NH elimination is the formation of isocyanate group. The formed primary product ion can further decompose to release HCl through a new transition state. A stable new aromatic product ion is formed with 10π electrons. Loss of C3H5NO neutral from another anionic isomer of the precursor ion was also observed and is characteristic for the amide terminal of the diamide functional group. A concerted mechanism is proposed, by which N–C bond breakage and cyclization of the eliminated neutral fragment C3H5NO takes place simultaneously to form 1-methyl-aziridin-2-one.
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Publikationstyp Artikel: Journalartikel
Dokumenttyp Wissenschaftlicher Artikel
Schlagwörter DCMU; DFT; FT-ICR; Energy barrier; Fragmentation mechanism
ISSN (print) / ISBN 1387-3806
Zeitschrift International Journal of Mass Spectrometry
Quellenangaben Band: 288, Heft: 1-3, Seiten: 6-15
Begutachtungsstatus Peer reviewed
Institut(e) Institute of Ecological Chemistry (IOEC)