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Formation of isomeric ethylenehalonium and α‐haloethyl cations and the role of ion–neutral complexes in the decomposition of protonated β‐haloethanols
Author(s) -
Heck Albert J. R.,
de Koning Leo J.,
Nibbering Nico M. M.
Publication year - 1993
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.1210280317
Subject(s) - protonation , chemistry , dissociation (chemistry) , molecule , halogen , photochemistry , bond cleavage , ion , decomposition , metastability , computational chemistry , organic chemistry , catalysis , alkyl
Decomposition of protonated β‐haloethanols was found to proceed predominantly via the loss of water. The mechanism was studied in the decomposition of metastable and collisionally activated isotopically labelled protonated β‐haloethanols. The study involved the characterization of the resulting fragment ions by collisionally activated decomposition and by low‐pressure ion/molecule probe reactions. The results indicate that loss of water from protonated β‐haloethanols proceeds via two competing mechanisms. The competition between these mechanisms appears to be governed by the nature of the halogen and by the internal energy of the decomposing protonated β‐haloethanol. In the first mechanism, loss of water is considered to be initiated by a concerted 1,2‐elimination of H 3 O + resulting in an ion–molecule complex between H 3 O + and haloethene. Rapid and reversible proton transfers between the two species in the complex is followed by a relatively slow dissociation ofthe intermediate complex resulting in the formation of an water molecule and an α‐haloethyl cation. In competition with this mechanism, loss of water can be initiated by carbon–oxygen bond cleavage, which is assisted by halogen–carbon bond formation resulting in the formation of a water molecule and cyclic ethylenehalonium ion.