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Unusual fragmentation of 1,1,2,2,3,3‐hexamethylindan. Methyl group equilibration and multi‐step skeletal rearrangements in the [M CH 3 ] + ions prior to the formation of t ‐C 4 H 9 + and other fragment ions
Author(s) -
Kuck Dietmar,
Mehdizadeh Ahmad
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.1210270416
Subject(s) - chemistry , fragmentation (computing) , ion , deuterium , kinetic energy , kinetic isotope effect , methyl group , isotope , electron ionization , hydrogen , analytical chemistry (journal) , medicinal chemistry , stereochemistry , group (periodic table) , ionization , atomic physics , organic chemistry , physics , quantum mechanics , computer science , operating system
Abstract Based on the surprising observation of an intense C 4 H 9 + ( m / z 57) peak in the electron impact mass spectrum, the fragmentation of 1,1,2,2,3,3‐hexamethylindan (2) was studied by mass‐analysed ion kinetic energy Spectrometry of its deuterium‐labelled analogues. While methyl loss from ions [2] + ˙ occurs with high selectivity (92%) from the positions 1 and 3 without any rearrangement, ions [2 CH 3 ] + undergo complete equilibration of the five methyl groups as intact entities. Subsequent multi‐step skeletal rearrangement of the [2 ‐ CH 3 ] + ions leads to formation of ferf‐butyl ions and to the loss of isobutene and propene, again without concomitant hydrogen exchange. Several kinetic isotope effects and also probably a thermodynamic isotope effect associated with each of these fragmentation processes have been found and their origin is discussed. The possibility of the formation of ion‐neutral complexes [ t ‐C 4 H 9 + C 10 H 10 ] aud [ s ‐C 3 H 7 + C 11 H 12 ] is considered on the basis of the labelling and reactivity pattern.