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Mass Spectrometric Decomposition Processes in Labelled 1‐Heptenes
Author(s) -
Falick Arnold M.,
Gäumann Tino
Publication year - 1976
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19760590403
Subject(s) - chemistry , ion , mass spectrum , molecule , allylic rearrangement , metastability , hydrogen , stereochemistry , cleavage (geology) , organic chemistry , catalysis , geotechnical engineering , fracture (geology) , engineering
The 70 eV mass spectra of a number of 13 C‐ and D‐labelled analogs of 1‐heptene have been measured, as well as the metastable transitions in the non‐labelled compound. Isotopic distributions in the major fragment ions have been calculated from the high and low resolution data. The results show that considerable skeletal rearrangement must take place before formation of most of the fragment ions. Loss of methyl and ethyl radicals occurs mainly from the two ends of the molecule. Ethylene fragments come primarily from the unsaturated end of the molecule, but show evidence of significant prior skeletal rearrangement. The predicted McLafferty rearrangement accounts for only 2/3 of the C 4 H 8 + ions formed, less for the C 3 H 6 + ions. At least 80% of C 4 H 9 + ions appear to be formed by allylic cleavage, as expected, but this mechanism can only account for a maximum of 20% of the formation of the complementary ion C 3 H 5 + . Both, this latter ion and C 3 H 6 + , are probably generated by loss of hydrogen from C 3 H 7 + . Figures obtained for label retention in 1‐[ 13 C]‐ and 1‐D‐labelled analogs were nearly identical for most fragment ions, probably indicating that the hydrogen atoms in position 1 remain on C(1) even following skeletal rearrangement. A similar result was found for the 7‐[ 13 C]‐ and 7‐D‐labelled compounds. The main exceptions in the case of the products labelled in position 1 (C 4 H 7 + , C 3 H 3 + ) seem to be due to initial loss of an hydrogen atom from this position followed by further fragmentation.