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2170 J. Am. Chem. SOC.1981, 103,2770-2780 Dissociative Ionization of Aryl-Substituted Vinyl Bromides in
 

Summary: 2170 J. Am. Chem. SOC.1981, 103,2770-2780
Dissociative Ionization of Aryl-Substituted Vinyl Bromides in
the Gas Phase: Experimental and Computational Evidence
for the Formation of Stable a-Arylvinyl Cations both by
Direct Means and Spontaneous Exothermic Isomerization of
Unstable Isomeric Ions
Yitzhak Apeloig,*lgWilfried Franke,lbZvi Rappoport,*leHelmut Schwarz,*lband
Daniel Stahlld
Contributionfrom the Institut fur Organische Chemie, der Technischen Universitat Berlin,
0-1000 Berlin 12, West Germany, the Departments of Organic Chemistry, The Hebrew University
of Jerusalem, Jerusalem, Israel, Technion-Israel Institute of Technology,Haifa, Israel, and the
Institut de Chimie Physique, Ecole Polytechnique FZdCrale de Lausanne, CH-1015 Lausanne,
Switzerland. Received August 1, 1980
Abstract: The kinetic energy release T which accompanies the Br- loss from ionized (E)- and (Z)-0-bromostyrenes (5 and
6) in the gas phase is higher by 0.7 *0.03 kcal mol-' than that from the molecular ion of a-bromostyrene (4). Together with
both collisional activation (CA) spectra and MO calculations this is interpreted as evidence for the direct formation of the
a-phenylvinyl cation 7 from 4'. and exothermic isomerization of the incipient [M - Br]' species formed from 5'. and 6's.
Exceptfor collision-induced CH2loss, the CA spectra of the C8H7+ions formed from 4'-, 5'., and 6'. and by chemicalionization
of henylacetylene are nearly identical. In the collision-inducedmethylene loss from the C8H7+ions derived from a-and
a partial degenerate isomerization prior to the CH2loss. The various possible cationic intermediates from the dissociative

  

Source: Apeloig, Yitzhak - Department of Chemistry, Technion, Israel Institute of Technology

 

Collections: Chemistry