93834-81-2Relevant articles and documents
Gas Phase Chemistry of Metastable Thiophene Cation Radicals
Franke, Helga,Halim, Herman,Schwarz, Helmut
, p. 3194 - 3204 (2007/10/02)
The unimolecular loss of acetylene from metastable thiophene cation radicals (1) has been studied by means of 13C and deuterium labelling and semi-empirical molecular orbital calculations (MINDO/3).It is shown that direct loss of acetylene from unrearranged 1 amounts to less than 5.3percent:1.2percent involving C-α/C-β and 4.1percent for loss of C-β/C-β for dissociations with lifetimes t ca. 10-5.5 s.More than 94percent of the long-lived molecular ions rearrange prior to dissociation, and it is shown that the majority of 1 (64.5percent) undergoes complete carbon atom scrambling, presumably via the tricyclic cation radical 12. 30.2percent of 1 suffer a degenerate isomerization involving either the pyramidal cation radical 11 or the bicyclic cation radicals 13, the latter undergoing a "Merry-go-round" rearrangement .At shorter lifetimes of 1 (t ca. 10-6.5 s) the isomerization pattern is only slightly changed.In agreement with previous kinetic studies of Butler and Baer it is shown by collisional activation mass spectrometry and the MINDO/3-study that the structure of the C2H2S+. ion generated from 1 is best described as that of the thioketene cation radical (18) and not of the isomeric mercaptoacetylene 21.The loss of both deuterated and 13C-labelled acetylene from labelled 1 is subject to a kinetic isotope effect. - The syntheses of the various isotopomers are described.
