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8705956 
Journal Article 
The Question of Reversible Formation of Bromonium Ions during the Course of Electrophilic Bromination of Olefins. 1. Formal Transfer of Br+to Scavenger Olefins from the Solvolytically Generated Bromonium Ions of Cyclohexene and Cyclopentene 
Brown, RS; Slebocka-Tilk, H; Buschek, JM; Kopecky, KR; Gedye, R 
1984 
Yes 
Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 
106 
16 
4515-4521 
English 
Traws-2-Bromo-l-[((4-bromophenyl)sulfonyl)oxy]cyclohexane and -cyclopentane (1 and 2), when solvolyzed at 75 °C in glacial acetic acid containing Br−and a scavenger olefin (cyclopentene for 1 and cyclohexene for 2) generate free molecular Br2as is evidenced by the formation of crossed products. 1 is more prone to yield crossed product than is 2. In the absence of added Br−, the amount of crossed product formed in the solvolysis is small. The results are interpreted in terms of competitive Br−capture of the intermediate bromonium ions produced during the course of solvolysis at Br+and carbon, the latter event leading to trans dibromide products of the starting material, while the former event generates Br2and olefin. The results of these experiments, when applied to electrophilic Br2addition to alkenes, strongly suggest that the intermediate bromonium ions are formed reversibly. Furthermore, evidence is presented which indicates that the bromonium ion of cyclohexene reverses to a greater extent than does the bromonium ion of cyclopentene. The demonstration of such reversibility of formation of bromonium ions from simple alkenes introduces a rather severe complication into the analysis of kinetic structure-reactivity data. These observations might be invoked to explain at least part of the 6–25-fold increase in reactivity in electrophilic addition of Br2exhibited by cyclopentene over cyclohexene. 1984, American Chemical Society. All rights reserved.