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Hydrogen migrations in mass spectrometry. IV—formation of [C 6 H 7 ] + in the chemical ionization mass spectra of alkylbenzenes
Author(s) -
Leung HeiWun,
Harrison Alex. G.
Publication year - 1977
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.1210120912
Subject(s) - alkylbenzenes , chemistry , alkyl , ethylbenzene , deuterium , mass spectrometry , mass spectrum , hydrogen , ring (chemistry) , chemical ionization , benzene , analytical chemistry (journal) , ionization , stereochemistry , organic chemistry , physics , atomic physics , ion , chromatography
Using specific deuterium labelling the mechanisms of the olefin elimination reactions leading to formation of [C 6 H 7 ]+ in the H 2 and CH 4 chemical ionizatin mass spectra of ethylbenzene and n ‐propylbenzene (and to [C 2 H 5 C 6 H 6 ]+ in the CH 4 chemical ionization mass spectra) have been investigated. The results show that the reaction does not occur by specific migration of H from the β position of the alkyl group to the benzene ring. For ethylbenzene 23–29% of the migrating H originates from the α‐position, while for n ‐propylbenzene H migration from all propyl positions is observed in the approximate ratio, position 1:position 2:position 3=0.30:0.22:0.48. It is proposed that the results can be explained on the basis of competing H migration from each alkyl position involving cyclic transition states of different ring sizes, rather than by H randomization within the alkyl chain.