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Further examples of skeletal rearrangements of the Wagner‐Meerwein type in chemical ionization mass spectrometry: The case of [C 6 H 9 ] + ions
Author(s) -
Gäumann Tino,
Houriet Raymond,
Stahl Daniel,
Tabet JeanClaude,
Heinrich Nikolaus,
Schwarz Helmut
Publication year - 1983
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.1210180508
Subject(s) - chemistry , ion , mass spectrometry , protonation , mndo , mass spectrum , electron ionization , standard enthalpy of formation , molecular orbital , analytical chemistry (journal) , fast atom bombardment , proton , crystallography , ionization , molecule , organic chemistry , physics , chromatography , quantum mechanics
The [C 6 H 9 ] + ions produced either via unimolecular H 2 O loss from 13 [C 6 H 11 O] + precursors or direct protonation of 1,3‐ and 1,4‐cyclohexadiene have identical collisional activation mass spectra. The kinetic energy release data for the process [C 6 H 11 O] + →[C 6 H 9 ] + +H 2 O are also very similar (on average T 0.5 =24 meV) irrespective of the constitution of the precursor. From the proton affinities of 1,3‐cyclohexadiene ( PA =837.2 kJ mol −1 ) using ion cyclotron resonance mass spectrometry the heat of formation of the [C 6 H 9 ] + ion is determined to 804.6 kJ mol −1 . This value taken together with the results of molecular orbital calculations (MNDO) and the structure indicative losses of CH 3 . and C 2 H 4 upon collisional activation suggest that the [C 6 H 9 ] + ion has the structure of the 1‐methylcyclopentenylium ion f and not that of the slightly less stable cyclohexenylium ion g. The generator of an easily interconverting system of isomeric [C 6 H 9 ] + ions is unlikely to be due to the high barrier separating the various isomers.