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Functional group interaction in the fragmentation of protonated 2,7‐octanedione
Author(s) -
Mueller Dieter R.,
Domon Bruno,
Blum Wolfgang,
Richter Wilhelm J.,
Reiner Hartmut,
Keller Rolf,
Fischer Peter
Publication year - 1989
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.1210240304
Subject(s) - chemistry , protonation , fragmentation (computing) , dissociation (chemistry) , ion , chemical ionization , aldol condensation , intramolecular force , medicinal chemistry , deuterium , mass spectrometry , kinetic isotope effect , reagent , tandem mass spectrometry , collision induced dissociation , stereochemistry , analytical chemistry (journal) , ionization , organic chemistry , physics , chromatography , quantum mechanics , computer science , catalysis , operating system
The fragmentation of 2,7‐octanedione, induced by chemical ionization with methane as a reagent gas (CI (CH 4 )), is shown to be extensively governed by the interaction of the two carbonyl groups. Tandem mass spectrometry reveals that a sequential loss of H 2 O and C 2 H 4 O from the [M + H] + ion competes with sequential loss of H 2 O and C 6 H 10 , and that both processes occur via the same [MH ‐ H 2 O] + intermediate. This intermediate is likely to be formed via intramolecular gas‐phase aldol condensation and subsequent dehydration. The resulting C(1) protonated 1‐acetyl‐2‐methylcyclopentene structure readily accounts for the observed further decomposition to CH 3 CO + and 1‐methylcyclopentene (C 6 H 10 ) or, alternatively, to [C 6 H 9 ] + (e. g. 1‐methylcyclopentenylium) ions and acetaldehyde (C 2 H 4 O). Support for this mechanistic rationale is derived from deuterium isotope labelling and low‐energy collision‐induced dissociation (CID) of the [MH ‐ H 2 O] + ion. The common intermediate shows a CID behaviour indistinguishable by these techniques from that of reference ions, which are produced by gas‐phase protonation of the authentic cyclic aldol or by gas‐phase addition of an acetyl cation to 1‐methylcyclopentene in a CI (CH 3 COOCH 3 ) experiment.