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The activation energy of the skeletal isomerization in the radical cations of toluene and cycloheptatriene by mass spectrometry of their 2‐phenylethyl derivatives
Author(s) -
Kuck Dietmar,
Grützmacher HansFr.
Publication year - 1979
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.1210140206
Subject(s) - chemistry , isomerization , cycloheptatriene , toluene , ion , mass spectrometry , ring (chemistry) , ionization energy , ionization , medicinal chemistry , organic chemistry , catalysis , chromatography
The Unimolecular mass spectrometric fragmentations of the molecular ions of 1,3‐diphenylpropane, 1‐(7‐cycloheptatrienyl)‐2‐phenylethane and the 1‐phenyl‐2‐tolylethanes and their [ d 5 ]phenyl analogues have been investigated by metastable ion techniques and measurements of ionization and appearance energies. By comparing the formation of [C 7 H 7 ] + , [C 7 H 8 ] + ⋅, [C 8 H 8 ] + ⋅ and [C 8 H 9 ] + it is shown that the molecular ions of the four diaryl isomers do not undergo ring expansion reactions of the aromatic nuclei prior to these fragmentations. Conversely, the molecular ions of the cycloheptatrienyl isomer suffer in part a contraction of the 7‐membered ring. From these results and from the measured ionization and appearance energies lower limits to the activation energies of these skeletal isomerizations have been estimated yielding E isom +> 33±5 kcal mol −1 formonoalkylbenzene, E isom +> 20 2±5 kc mol −1 for 7‐alkylcycloheptatriene and E isom +> 40±5 kcal mol −1 for dialkylvbenzene positive radical ions. Upper limits can be deduced from literature evidence yielding E isom +< 45 kcal mol −1 for monoalkylbenzene and E isom +< 53 kcal 4mol −1 for dialkylbenzene positive radical ions. The activation energy thus estimated for monoalkylbenzene is in excellent agreement with the recently calculated value(s) for the toluene ion.