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Loss of methyl from [H 2 CC(OH)CH 3 ] +˙ ions prepared by electron impact ionization of unstable 2‐hydroxypropene
Author(s) -
Tureček František,
Hanuš Vladimír
Publication year - 1984
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.1210191209
Subject(s) - ion , chemistry , fragmentation (computing) , electron ionization , deuterium , methylene , isomerization , ionization , hydrogen , kinetic isotope effect , hydrogen atom , analytical chemistry (journal) , chemical ionization , medicinal chemistry , atomic physics , organic chemistry , physics , catalysis , alkyl , computer science , operating system
Unstable 2‐hydroxpropene was prepared by retro‐Diels‐Alder decomposition of 5‐ exo ‐methyl‐5‐norbornenol at 800°C/2 × 10 −6 Torr. The ionization energy of 2‐hydroxypropene was measured as 8.67±0.05 eV. Formation of [C 2 H 3 O] + and [CH 3 ] + ions originating from different parts of the parent ion was examined by means of 13 C and deuterium labelling. Threshold‐energy [H 2 CC(OH)CH 3 ] +˙ ions decompose to CH 3 CO + +CH 3 ˙ with appearance energy AE (CH 3 CO + ) = 11.03 ± 0.03 eV. Higher energy ions also form CH 2 COH + + CH 3 with appearance energy AE (CH 2 COH + ) = 12.2–12.3 eV. The fragmentation competes with hydrogen migration between C(1) and C(3) in the parent ion. [C 2 H 3 O] + ions containing the original methyl group and [CH 3 ] + ions incorporating the former methylene and the hydroxyl hydrogen atom are formed preferentially, compared with their corresponding counterparts. This behaviour is due to rate‐determining isomerization [H 2 CC(OH)CH 3 ] +˙ →[CH 3 COCH 3 ] +˙ , followed by asymmetrical fragmentation of the latter ions. Effects of internal energy and isotope substitution are discussed.